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Polymers, Volume 9, Issue 6 (June 2017)

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Cover Story This paper reports the principal discoveries which have played a major role in the polyolefin field [...] Read more.
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Open AccessArticle Combining ATRP and FRP Gels: Soft Gluing of Polymeric Materials for the Fabrication of Stackable Gels
Polymers 2017, 9(6), 186; doi:10.3390/polym9060186
Received: 7 May 2017 / Revised: 20 May 2017 / Accepted: 20 May 2017 / Published: 24 May 2017
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Abstract
Stackable gels comprised of layers of dissimilar polymers were synthesized by combining conventional free radical polymerization (FRP) and atom transfer radical polymerization (ATRP) using two approaches: (i) polymerization of a pre-gel solution containing a monomer and cross-linker introduced on top of a previously
[...] Read more.
Stackable gels comprised of layers of dissimilar polymers were synthesized by combining conventional free radical polymerization (FRP) and atom transfer radical polymerization (ATRP) using two approaches: (i) polymerization of a pre-gel solution containing a monomer and cross-linker introduced on top of a previously prepared gel, and (ii) simultaneous polymerization of two immiscible pre-gel solutions remaining in contact. All permutations of FRP and ATRP yielded single-piece, connected, amphiphilic gels regardless of the order of polymerization. Furthermore, multi-layer ATRP gels combining different polymers were synthesized with the FRP layer as a gluing agent. A 10-layer amphiphilic stackable gel combining n-butyl methacrylate (BMA) and 2-(dimethylamino)ethyl methacrylate (DMAEMA), and a 10-layer stackable gel combining BMA, DMAEMA and di(ethylene glycol) methyl ether methacrylate (PEO2MA) were synthesized. This patching method, combining conventional FRP gels with ATRP ones, offers an efficient path to the formation of complex stackable gel architectures. Full article
(This article belongs to the Special Issue Functionally Responsive Polymeric Materials)
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Open AccessArticle Effect of High Salt Concentration (HSC) on Structural, Morphological, and Electrical Characteristics of Chitosan Based Solid Polymer Electrolytes
Polymers 2017, 9(6), 187; doi:10.3390/polym9060187
Received: 16 April 2017 / Revised: 17 May 2017 / Accepted: 19 May 2017 / Published: 24 May 2017
Cited by 2 | PDF Full-text (2773 KB) | HTML Full-text | XML Full-text
Abstract
Chitosan (CS) films doped with sodium triflate (NaTf) were prepared by the solution cast technique. The structural and morphological behaviors of the samples were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The XRD patterns were deconvoluted to estimate the
[...] Read more.
Chitosan (CS) films doped with sodium triflate (NaTf) were prepared by the solution cast technique. The structural and morphological behaviors of the samples were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The XRD patterns were deconvoluted to estimate the degree of crystallinity of the samples. The SEM micrograph showed the crystalline structure of the sample contained 50 wt % of NaTf salt. The disappearance of broad peaks of chitosan at 2θ ≈ 21° and 2θ ≈ 32° confirmed the occurrence of ion association at 50 wt % of NaTf salt. In impedance plots, a low frequency spike region and a high frequency semicircle, were distinguishable for low salt concentrations. The highest ambient temperature direct current (DC) electrical conductivity obtained for CS:NaTf was found to be 2.41 × 104 S/cm for the sample containing 40 wt % of NaTf salt. The role of lattice energy of salts on DC ionic conductivity was also discussed. The temperature dependence of DC conductivity was found to follow the well-known Arrhenius relationship. From the alternating current (AC) conductivity spectra, three distinct regions were recognized for the samples with NaTf salt concentration ranging from 10 wt % to 30 wt %. The plateau region of AC spectra was used to estimate the DC conductivity. Full article
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Open AccessArticle Unfolding Kinetics of a Wormlike Chain under Elongational Flow
Polymers 2017, 9(6), 190; doi:10.3390/polym9060190
Received: 20 April 2017 / Revised: 19 May 2017 / Accepted: 24 May 2017 / Published: 26 May 2017
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Abstract
A simple theory of the unfolding kinetics of a semi-flexible polymer chain is presented in terms of a Kramers type picture for the energy of elongation. The hydrodynamic interactions are discussed in terms of slender body theory. It turns out that the elongation
[...] Read more.
A simple theory of the unfolding kinetics of a semi-flexible polymer chain is presented in terms of a Kramers type picture for the energy of elongation. The hydrodynamic interactions are discussed in terms of slender body theory. It turns out that the elongation of the chain is basically linear in time and independent of the viscosity. The former prediction agrees with experiments on the stretching dynamics of DNA under planar elongational flow. Nevertheless, the theory overestimates the experimental rate by a significant amount for reasons that are unclear. Full article
(This article belongs to the Special Issue Semiflexible Polymers)
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Open AccessArticle In Vitro Biocompatibility, Radiopacity, and Physical Property Tests of Nano-Fe3O4 Incorporated Poly-l-lactide Bone Screws
Polymers 2017, 9(6), 191; doi:10.3390/polym9060191
Received: 18 April 2017 / Revised: 20 May 2017 / Accepted: 24 May 2017 / Published: 26 May 2017
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Abstract
The aim of this study was to fabricate biodegradable poly-l-lactic acid (PLLA) bone screws containing iron oxide (Fe3O4) nanoparticles, which are radiopaque and 3D-printable. The PLLA composites were fabricated by loading 20%, 30%, and 40% Fe3O4
[...] Read more.
The aim of this study was to fabricate biodegradable poly-l-lactic acid (PLLA) bone screws containing iron oxide (Fe3O4) nanoparticles, which are radiopaque and 3D-printable. The PLLA composites were fabricated by loading 20%, 30%, and 40% Fe3O4 nanoparticles into the PLLA. The physical properties, including elastic modulus, thermal properties, and biocompatibility of the composites were tested. The 20% nano-Fe3O4/PLLA composite was used as the material for fabricating the 3D-printed bone screws. The mechanical performance of the nano-Fe3O4/PLLA bone screws was evaluated by anti-bending and anti-torque strength tests. The tissue response and radiopacity of the nano-Fe3O4/PLLA bone screws were assessed by histologic and CT imaging studies using an animal model. The addition of nano-Fe3O4 increased the crystallization of the PLLA composites. Furthermore, the 20% nano-Fe3O4/PLLA composite exhibited the highest thermal stability compared to the other Fe3O4 proportions. The 3D-printed bone screws using the 20% nano-Fe3O4/PLLA composite provided excellent local tissue response. In addition, the radiopacity of the 20% nano-Fe3O4/PLLA screw was significantly better compared with the neat PLLA screw. Full article
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Open AccessCommunication A Rapid One-Pot Synthesis of Novel High-Purity Methacrylic Phosphonic Acid (PA)-Based Polyhedral Oligomeric Silsesquioxane (POSS) Frameworks via Thiol-Ene Click Reaction
Polymers 2017, 9(6), 192; doi:10.3390/polym9060192
Received: 9 May 2017 / Revised: 24 May 2017 / Accepted: 24 May 2017 / Published: 27 May 2017
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Abstract
Herein, we demonstrate a facile methodology to synthesis a novel methacrylic phosphonic acid (PA)-functionalized polyhedral oligomeric silsesquioxanes (POSSs) via thiol-ene click reaction using octamercapto thiol-POSS and ethylene glycol methacrylate phosphate (EGMP) monomer. The presence of phosphonic acid moieties and POSS-cage structure in POSS-S-PA
[...] Read more.
Herein, we demonstrate a facile methodology to synthesis a novel methacrylic phosphonic acid (PA)-functionalized polyhedral oligomeric silsesquioxanes (POSSs) via thiol-ene click reaction using octamercapto thiol-POSS and ethylene glycol methacrylate phosphate (EGMP) monomer. The presence of phosphonic acid moieties and POSS-cage structure in POSS-S-PA was confirmed by Fourier transform infrared (FT-IR) and nuclear magnetic resonance (1H, 29Si and 31P-NMR) analyses. Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrum of POSS-S-PA acquired in a dithranol matrix, which has specifically designed for intractable polymeric materials. The observed characterization results signposted that novel organo-inorganic hybrid POSS-S-PA would be an efficacious material for fuel cells as a proton exchange membrane and high-temperature applications due to its thermal stability of 380 °C. Full article
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Open AccessArticle N,N-Dimethylformamide (DMF) Usage in Epoxy/Graphene Nanocomposites: Problems Associated with Reaggregation
Polymers 2017, 9(6), 193; doi:10.3390/polym9060193
Received: 21 April 2017 / Revised: 20 May 2017 / Accepted: 24 May 2017 / Published: 27 May 2017
Cited by 2 | PDF Full-text (2810 KB) | HTML Full-text | XML Full-text
Abstract
DMF is one the most commonly-used solvents for preparing graphene nanocomposites. Various processing variables for DMF are being used for the preparation of epoxy/graphene nanocomposites. Whilst the emphasis of all of these reported studies are on the improvements in mechanical, and other properties,
[...] Read more.
DMF is one the most commonly-used solvents for preparing graphene nanocomposites. Various processing variables for DMF are being used for the preparation of epoxy/graphene nanocomposites. Whilst the emphasis of all of these reported studies are on the improvements in mechanical, and other properties, of the epoxy/graphene nanocomposites, there is no study investigating how DMF affects the processing and how it is associated with the final properties of the nanocomposites. In this work, different dosages of DMF have been used to prepare nanocomposites. Mechanical testing, X-ray diffraction (XRD), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM) have been used to analyze the effectiveness of DMF dosage on the properties of processed nanocomposites. Larger dosages of DMF are not always ideal for dispersing graphene as it promotes reaggregation of graphene during the processing. Full article
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Open AccessArticle Synthesis of Polymer Nanocomposites Based on [Methyl Cellulose](1−x):(CuS)x (0.02 M ≤ x ≤ 0.08 M) with Desired Optical Band Gaps
Polymers 2017, 9(6), 194; doi:10.3390/polym9060194
Received: 30 April 2017 / Revised: 22 May 2017 / Accepted: 25 May 2017 / Published: 30 May 2017
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Abstract
In this paper, the sample preparation of polymer nanocomposites based on methyl cellulose (MC) with small optical bandgaps has been discussed. Copper monosulfide (CuS) nanoparticles have been synthesized from the sodium sulphide (Na2S) and copper chloride (CuCl2) salts. Distinguishable
[...] Read more.
In this paper, the sample preparation of polymer nanocomposites based on methyl cellulose (MC) with small optical bandgaps has been discussed. Copper monosulfide (CuS) nanoparticles have been synthesized from the sodium sulphide (Na2S) and copper chloride (CuCl2) salts. Distinguishable localized surface resonance plasmon (LSRP) absorption peaks for CuS nanoparticles within the 680–1090 nm scanned wavelength range were observed for the samples. An absorption edge (Ed) was found to be widely shifted to a lower photon energy region. A linear relationship between the refractive index of the samples and the CuS fraction was utilized to describe the distribution of the particle. The optical bandgap of MC was reduced from 6.2 to 2.3 eV upon the incorporation of 0.08 M of CuS nanoparticles. The optical dielectric loss, as an alternative method, was used successfully to estimate the optical bandgap. Moreover, the electronic transition type was identified by using Tauc’s extrapolation method. The plots of the optical dielectric constant and energy bandgap as a function of the CuS concentration were utilized to examine the validity of the Penn model. For the nanocomposite samples, the Urbach energy was found to be increased, which can be evidence for a large possible number of bands-to-tail and tail-to-tail transitions. However, from the X-ray diffraction (XRD) analysis, it was also found that the synthesized CuS nanoparticles disrupted the crystallinity phase of the MC polymer. Finally, fourier transform infrared (FTIR) spectroscopy for the samples was also performed. Significant decreases of transmittance intensity as well as band shifting in the FTIR spectra were observed for the doped samples. Full article
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Open AccessArticle Effect of Interfacial Polarization and Water Absorption on the Dielectric Properties of Epoxy-Nanocomposites
Polymers 2017, 9(6), 195; doi:10.3390/polym9060195
Received: 20 April 2017 / Revised: 21 May 2017 / Accepted: 23 May 2017 / Published: 28 May 2017
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Abstract
Five types of nanofillers, namely, silica, surface-silylated silica, alumina, surface-silylated alumina, and boron nitride, were tested in this study. Nanocomposites composed of an epoxy/amine resin and one of the five types of nanoparticles were tested as dielectrics with a focus on (i) the
[...] Read more.
Five types of nanofillers, namely, silica, surface-silylated silica, alumina, surface-silylated alumina, and boron nitride, were tested in this study. Nanocomposites composed of an epoxy/amine resin and one of the five types of nanoparticles were tested as dielectrics with a focus on (i) the surface functionalization of the nanoparticles and (ii) the water absorption by the materials. The dispersability of the nanoparticles in the resin correlated with the composition (OH content) of their surfaces. The interfacial polarization of the thoroughly dried samples was found to increase at lowered frequencies and increased temperatures. The β relaxation, unlike the interfacial polarization, was not significantly increased at elevated temperatures (below the glass-transition temperature). Upon the absorption of water under ambient conditions, the interfacial polarization increased significantly, and the insulating properties decreased or even deteriorated. This effect was most pronounced in the nanocomposite containing silica, and occurred as well in the nanocomposites containing silylated silica or non-functionalized alumina. The alternating current (AC) breakdown strength of all specimens was in the range of 30 to 35 kV·mm−1. In direct current (DC) breakdown tests, the epoxy resin exhibited the lowest strength of 110 kV·mm−1; the nanocomposite containing surface-silylated alumina had a strength of 170 kV·mm−1. In summary, water absorption had the most relevant impact on the dielectric properties of nanocomposites containing nanoparticles, the surfaces of which interacted with the water molecules. Nanocomposites containing silylated alumina particles or boron nitride showed the best dielectric properties in this study. Full article
(This article belongs to the Special Issue Polymer Nanocomposites)
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Open AccessArticle Efficient Sampling of Knotting-Unknotting Pathways for Semiflexible Gaussian Chains
Polymers 2017, 9(6), 196; doi:10.3390/polym9060196
Received: 10 May 2017 / Revised: 17 May 2017 / Accepted: 19 May 2017 / Published: 29 May 2017
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Abstract
We propose a stochastic method to generate exactly the overdamped Langevin dynamics of semi-flexible Gaussian chains, conditioned to evolve between given initial and final conformations in a preassigned time. The initial and final conformations have no restrictions, and hence can be in any
[...] Read more.
We propose a stochastic method to generate exactly the overdamped Langevin dynamics of semi-flexible Gaussian chains, conditioned to evolve between given initial and final conformations in a preassigned time. The initial and final conformations have no restrictions, and hence can be in any knotted state. Our method allows the generation of statistically independent paths in a computationally efficient manner. We show that these conditioned paths can be exactly generated by a set of local stochastic differential equations. The method is used to analyze the transition routes between various knots in crossable filamentous structures, thus mimicking topological reconnections occurring in soft matter systems or those introduced in DNA by topoisomerase enzymes. We find that the average number of crossings, writhe and unknotting number are not necessarily monotonic in time and that more complex topologies than the initial and final ones can be visited along the route. Full article
(This article belongs to the Special Issue Knotted and Catenated Polymers)
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Open AccessArticle Apoptin Gene Delivery by the Functionalized Polyamidoamine (PAMAM) Dendrimer Modified with Ornithine Induces Cell Death of HepG2 Cells
Polymers 2017, 9(6), 197; doi:10.3390/polym9060197
Received: 10 March 2017 / Revised: 23 May 2017 / Accepted: 24 May 2017 / Published: 29 May 2017
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Abstract
The use of tumor-specific therapeutic agents is a promising option for efficient and safe nonviral gene transfer in gene therapy. In this study, we describe the efficacy of polyamidoamine (PAMAM)-based nonviral gene delivery carriers, namely, an ornithine conjugated PAMAM (PAMAM-O) dendrimer in delivering
[...] Read more.
The use of tumor-specific therapeutic agents is a promising option for efficient and safe nonviral gene transfer in gene therapy. In this study, we describe the efficacy of polyamidoamine (PAMAM)-based nonviral gene delivery carriers, namely, an ornithine conjugated PAMAM (PAMAM-O) dendrimer in delivering apoptin, a tumor-specific killer gene, into human hepatocellular carcinoma (HepG2 cells) and dermal fibroblasts. We analyzed the transfection efficiency by the luciferase assay and assessed cell viability in both cell types. The transfection efficiency of the PAMAM-O dendrimer was found to be higher than that of the PAMAM dendrimer. Moreover, the cytotoxicity of the PAMAM-O dendrimer was very low. We treated both cell types with a polyplex of PAMAM-O dendrimer with apoptin, and analyzed its cellular uptake and localization by confocal microscopy. Cell cycle distribution, tetramethylrhodamine, ethyl ester (TMRE) analysis, and transmission electron microscopy imaging showed that apoptin induced cell death in HepG2 cells. We therefore demonstrated that a PAMAM-O/apoptin polyplex can be used as an effective therapeutic strategy in cancer owing to its effectiveness as a suitable nonviral gene vector for gene therapy. Full article
(This article belongs to the Special Issue Polymers and Nanogels for Gene Therapy)
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Open AccessArticle Volume Hologram Formation in SU-8 Photoresist
Polymers 2017, 9(6), 198; doi:10.3390/polym9060198
Received: 14 April 2017 / Revised: 25 May 2017 / Accepted: 27 May 2017 / Published: 30 May 2017
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Abstract
In order to further understand the mechanism of volume hologram formation in photosensitive polymers, light-induced material response is analyzed in commonly used epoxy-based negative photoresist Epon SU-8. For this purpose, time-resolved investigation of volume holographic grating growth is performed in the SU-8 based
[...] Read more.
In order to further understand the mechanism of volume hologram formation in photosensitive polymers, light-induced material response is analyzed in commonly used epoxy-based negative photoresist Epon SU-8. For this purpose, time-resolved investigation of volume holographic grating growth is performed in the SU-8 based host–guest system and in the pure SU-8 material, respectively. The comparison of grating growth curves from doped and undoped system allows us to draw conclusions on the impact of individual components on the grating formation process. The successive formation of transient absorption as well as phase gratings in SU-8 is observed. Influence of exposure duration and UV flood cure on the grating growth are investigated. Observed volume holographic grating formation in SU-8 can be explained based on the generation and subsequent diffusion of photoacid as well as time-delayed polymerization of exposed and unexposed areas. Full article
(This article belongs to the Special Issue Photo-Responsive Polymers)
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Open AccessArticle Nano-Contact Transfer with Gold Nanoparticles on PEG Hydrogels and Using Wrinkled PDMS-Stamps
Polymers 2017, 9(6), 199; doi:10.3390/polym9060199
Received: 1 April 2017 / Revised: 13 May 2017 / Accepted: 17 May 2017 / Published: 31 May 2017
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Abstract
In the present work, a soft lithographic process is used to create nanometer-sized line patterns of gold nanoparticles (Au NPs) on PEG-based hydrogels. Hereby nanometer-sized wrinkles on polydimethylsiloxane (PDMS) are first fabricated, then functionalized with amino-silane and subsequently coated with Au NPs. The
[...] Read more.
In the present work, a soft lithographic process is used to create nanometer-sized line patterns of gold nanoparticles (Au NPs) on PEG-based hydrogels. Hereby nanometer-sized wrinkles on polydimethylsiloxane (PDMS) are first fabricated, then functionalized with amino-silane and subsequently coated with Au NPs. The Au NPs are electrostatically bound to the surface of the wrinkled PDMS. In the next step, these relatively loosely bound Au NPs are transferred to PEG based hydrogels by simple contacting, which we denote “nano-contact transfer”. Nano-patterned Au NPs lines on PEG hydrogels are thus achieved, which are of interesting potential in nano-photonics, biosensor applications (using SERS) and to control nanoscopic cell adhesion events. Full article
(This article belongs to the Special Issue Bio-inspired and Bio-based Polymers)
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Open AccessArticle Performance and Kinetics Study of Self-Repairing Hydroxyl-Terminated Polybutadiene Binders Based on the Diels–Alder Reaction
Polymers 2017, 9(6), 200; doi:10.3390/polym9060200
Received: 11 May 2017 / Revised: 26 May 2017 / Accepted: 26 May 2017 / Published: 30 May 2017
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Abstract
Based on the Diels–Alder reaction and hydroxyl-terminated polybutadiene (HTPB) binders of solid propellants, two novel compounds—furfuryl-terminated polybutadiene (FTPB) and trifurfuryl propane (TFP)—were designed and synthesized, and their structures were characterized. A new kind of reversible Diels–Alder reaction system was formed by FTPB as
[...] Read more.
Based on the Diels–Alder reaction and hydroxyl-terminated polybutadiene (HTPB) binders of solid propellants, two novel compounds—furfuryl-terminated polybutadiene (FTPB) and trifurfuryl propane (TFP)—were designed and synthesized, and their structures were characterized. A new kind of reversible Diels–Alder reaction system was formed by FTPB as main resin, N,N′-1,3-phenylenedimaleimide (PDMI) as curing agent and TFP as chain extender. The results showed that this system had good mechanical properties with a tensile strength of 1.76 MPa and a tensile strain of 284% after curing, and the repair efficiency of the crack was 88%. Therefore, it could be used as a novel binder of energetic materials such as solid propellant and PBX explosives to provide them with self-repairing characteristics and improve the reliability for application. Full article
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Open AccessArticle The Poly(acrylonitrule-co-acrylic acid)-graft-β-cyclodextrin Hydrogel for Thorium(IV) Adsorption
Polymers 2017, 9(6), 201; doi:10.3390/polym9060201
Received: 18 February 2017 / Revised: 22 May 2017 / Accepted: 25 May 2017 / Published: 31 May 2017
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Abstract
In this report, the β-CD(AN-co-AA) hydrogel was used to remove the thorium(IV) [Th(IV)] from the water system, and the new adsorbent was characterized through Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The influences of contact
[...] Read more.
In this report, the β-CD(AN-co-AA) hydrogel was used to remove the thorium(IV) [Th(IV)] from the water system, and the new adsorbent was characterized through Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The influences of contact time, pH value, ionic strength, solid-liquid ratio, initial Th(IV) concentration, and temperature on Th(IV) adsorption onto the functional hydrogel were researched. The results showed that the experimental data followed the Langmuir isotherm and the maximum adsorption capacity (qmax) for Th(IV) was 692 mg/g at pH 2.95, which approached the calculated (qe) 682 mg/g. The desorption capacity of Th(IV) in different HNO3 concentrations ranging from 0.005 to 0.5 M was also studied, and the percentage of the maximum desorption was 86.85% in the condition of 0.09 M HNO3. The selectivity of β-CD(AN-co-AA) hydrogel was also be studied, the results indicated that this material retained the good adsorption capacity to Th(IV) even when the Ca2+, Mg2+, or Pb2+ existed in the system. The findings indicate that β-CD(AN-co-AA) can be used as a new candidate for the enrichment and separation of Th(IV), or its analogue actinides, from large-volume solution in practical application. Full article
(This article belongs to the Special Issue Electroactive Polymers and Gels)
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Open AccessArticle New Mechanism Proposed for the Base-Catalyzed Urea–Formaldehyde Condensation Reactions: A Theoretical Study
Polymers 2017, 9(6), 203; doi:10.3390/polym9060203
Received: 12 May 2017 / Revised: 27 May 2017 / Accepted: 27 May 2017 / Published: 2 June 2017
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Abstract
Base-catalyzed urea–formaldehyde condensation reactions were investigated by using a quantum chemistry method. It was found that monomethylolurea or N,N’-dimethylolurea can produce the methyleneurea intermediate (–HN–CO–N=CH2) with the catalysis of base. The E1cb (unimolecular elimination of conjugate base) mechanism
[...] Read more.
Base-catalyzed urea–formaldehyde condensation reactions were investigated by using a quantum chemistry method. It was found that monomethylolurea or N,N’-dimethylolurea can produce the methyleneurea intermediate (–HN–CO–N=CH2) with the catalysis of base. The E1cb (unimolecular elimination of conjugate base) mechanism was identified for the formation of such an intermediate. The potential energy barrier was theoretically predicted to be 59.6 kJ/mol for the E1cb step, which is about half of that of previously proposed SN2 (bimolecular nucleophilic substitution) mechanism. In the subsequentcondensation reactions, Michael addition reactions that lead to different condensed structures can occur between the methyleneurea intermediate and the anions produced from methylolureas under alkaline conditions. Based on the theoretical calculations on the kinetics and thermodynamics of the selected reactions, the competitive formations of methylene linkages, ether linkages and uron were discussed in combination with our previous experimental observations. Full article
(This article belongs to the collection Polymeric Adhesives)
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Open AccessArticle Epoxidized Jatropha Oil as a Sustainable Plasticizer to Poly(lactic Acid)
Polymers 2017, 9(6), 204; doi:10.3390/polym9060204
Received: 3 May 2017 / Revised: 26 May 2017 / Accepted: 31 May 2017 / Published: 2 June 2017
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Abstract
A renewable resource, epoxidized jatropha oil (EJO), was used as a green plasticizer and added to poly(lactic acid) (PLA). EJO was compounded into PLA at different contents. The addition of 3 wt % EJO to the PLA demonstrates significant improvement in flexibility, which
[...] Read more.
A renewable resource, epoxidized jatropha oil (EJO), was used as a green plasticizer and added to poly(lactic acid) (PLA). EJO was compounded into PLA at different contents. The addition of 3 wt % EJO to the PLA demonstrates significant improvement in flexibility, which leads to a percentage increase of about 7000% in elongation at break. This tensile result was confirmed by surface morphology analysis with clear proof of plastic deformation in EJO-plasticized PLA. EJO imparts a good heat stabilization effect. Thermal stability of PLA was enhanced upon addition of EJO, which is due to their good interaction and plasticizer dispersion within the PLA matrix. This EJO-plasticized PLA has wide applications in various industries, such as packaging of food and non-food products. Full article
(This article belongs to the Special Issue Biodegradable and Biobased Polyesters)
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Open AccessArticle Two Ways to Examine Differential Constitutive Equations: Initiated on Steady or Initiated on Unsteady (LAOS) Shear Characteristics
Polymers 2017, 9(6), 205; doi:10.3390/polym9060205
Received: 21 April 2017 / Revised: 29 May 2017 / Accepted: 1 June 2017 / Published: 3 June 2017
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Abstract
The exponential Phan–Tien and Tanner (PTT), Giesekus, Leonov, and modified extended Pom–Pom (mXPP) differential constitutive models are evaluated in two ways: with regard to steady shear characteristics and with regard to large amplitude oscillatory shear characteristics of a solution of poly(ethylene oxide) in
[...] Read more.
The exponential Phan–Tien and Tanner (PTT), Giesekus, Leonov, and modified extended Pom–Pom (mXPP) differential constitutive models are evaluated in two ways: with regard to steady shear characteristics and with regard to large amplitude oscillatory shear characteristics of a solution of poly(ethylene oxide) in dimethyl sulfoxide. Efficiency of the models with nonlinear parameters optimized with respect to steady shear measurements is evaluated by their ability to describe large amplitude oscillatory shear (LAOS) characteristics. The reciprocal problem is also analyzed: The nonlinear parameters are optimized with respect to the LAOS measurements, and the models are confronted with the steady shear characteristics. In this case, optimization is based on the LAOS measurements and equal emphasis is placed on both real and imaginary parts of the stress amplitude. The results show that the chosen models are not adequately able to fit the LAOS characteristics if the optimization of nonlinear parameters is based on steady shear measurements. It follows that the optimization of nonlinear parameters is much more responsible if it is carried out with respect to the LAOS data. In this case, when the optimized parameters are used for a description of steady shear characteristics, efficiency of the individual models as documented differs. Full article
(This article belongs to the Special Issue Complex Fluid Rheology)
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Open AccessArticle Analysis of the Cross-Linking Reaction of Lignin with Triethyl Phosphate by MALDI-TOF and 13C NMR
Polymers 2017, 9(6), 206; doi:10.3390/polym9060206
Received: 4 April 2017 / Revised: 31 May 2017 / Accepted: 2 June 2017 / Published: 4 June 2017
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Abstract
The reaction of condensation and cross-linking of desulfurized kraft lignin with triethyl phosphate (TEP) was explored. Catechol, a simple model of the aromatic ring of lignin, and glycerol, a model compound of the aliphatic hydroyl groups of the side chain of lignin, were
[...] Read more.
The reaction of condensation and cross-linking of desulfurized kraft lignin with triethyl phosphate (TEP) was explored. Catechol, a simple model of the aromatic ring of lignin, and glycerol, a model compound of the aliphatic hydroyl groups of the side chain of lignin, were employed under similar reaction conditions. Solid state cross-polarisation/magic-angle spinning (CP-MAS) 13C NMR and matrix assisted laser desorption ionization time-of-flight (MALDI-TOF) spectroscopy studies showed that polycondensation occurs on phenolic hydroxyl groups of lignin, as well as on aliphatic hydroxyls groups of its side chain. The reactions appear to be favoured by higher temperatures and in the presence of ammonia. Preliminary adhesion tests on wood shown good hydrophobicity properties of the surface treated with lignin-TEP-based resin. Initial application tests carried out at high temperature demonstrated as good performance as metallic coating. Full article
(This article belongs to the collection Polymeric Adhesives)
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Open AccessArticle Unique Halloysite Nanotubes–Polyvinyl Alcohol–Polyvinylpyrrolidone Composite Complemented with Physico–Chemical Characterization
Polymers 2017, 9(6), 207; doi:10.3390/polym9060207
Received: 11 May 2017 / Revised: 27 May 2017 / Accepted: 30 May 2017 / Published: 6 June 2017
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Abstract
A halloysite nanotubes–polyvinyl alcohol–polyvinylpyrrolidone (HNTs–PVA–PVP) composite has been investigated for a quite long time aiming at improving the physico–chemical characterization of HNTs. In this work, HNTs–PVA–PVP composite were prepared based on a unique procedure characterized by crosslinking two polymers with HNTs. The composite
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A halloysite nanotubes–polyvinyl alcohol–polyvinylpyrrolidone (HNTs–PVA–PVP) composite has been investigated for a quite long time aiming at improving the physico–chemical characterization of HNTs. In this work, HNTs–PVA–PVP composite were prepared based on a unique procedure characterized by crosslinking two polymers with HNTs. The composite of two polymers were modified by treating HNTs with phosphoric acid (H3PO4) and by using malonic acid (MA) as a crosslinker. The composite was also treated by adding the dispersion agent sodium dodecyl sulfate (SDS). The HNTs–PVA–PVP composite shows better characteristics regarding agglomeration when HNTs is treated in advance by H3PO4. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), brunauer–emmett–teller (BET), size distribution, and atomic force microscopy (AFM) are used to characterize the physio-chemical properties of the composite. FTIR shows additional peaks at 2924.29, 1455.7, and 682.4 cm−1 compared to the neat HNTs due to adding MA. Despite that, the XRD spectra do not show a significant difference, the decrease in peak intensity could be attributed to the addition of semi-crystalline PVA and the amorphous PVP. The images taken by TEM and FESEM show the possible effects of MA on the morphology and internal feature of HNTs–PVA–PVP composite treated by MA by showing the deformation of the matrix. The BET surface area increased to 121.1 m2/g compared to the neat HNTs at 59.1 m2/g. This result, the second highest recorded result, is considered a breakthrough in enhancing the properties of HNTs–PVA–PVP composite, and treatment by MA crosslinking may attribute to the size and the number of the pores. The results from these techniques clearly showed that a significant change has occurred for treated HNTs–PVA–PVP composite where MA was added. The characterization of HNTs–PVA–PVP composite with and without treating HNTs and using crosslinker may lead to a better understanding of this new composites as a precursor to possible applications in the dentistry field. Full article
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Open AccessArticle Preparation and Characterization of Quaternized Chitosan Coated Alginate Microspheres for Blue Dextran Delivery
Polymers 2017, 9(6), 210; doi:10.3390/polym9060210
Received: 1 May 2017 / Revised: 30 May 2017 / Accepted: 5 June 2017 / Published: 7 June 2017
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Abstract
In this study, 2-[(Acryloyloxy)ethyl]trimethylammonium chloride was graft polymerized onto chitosan (CS) to form quaternary ammonium CS (QAC) by using ammonium persulfate as a redox initiator. Alginate (ALG) microspheres loaded with a water-soluble macromolecular model drug, blue dextran (BD), were obtained by corporation of
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In this study, 2-[(Acryloyloxy)ethyl]trimethylammonium chloride was graft polymerized onto chitosan (CS) to form quaternary ammonium CS (QAC) by using ammonium persulfate as a redox initiator. Alginate (ALG) microspheres loaded with a water-soluble macromolecular model drug, blue dextran (BD), were obtained by corporation of coaxial gas-flow method and ionic gelation process. CS and QAC were then coated on the surfaces of ALG microspheres to generate core/shell structured CS/ALG and QAC/ALG microspheres, respectively. The experiment result showed that QAC/ALG microspheres had a smaller particle size due to the stronger electrostatic interactions between QAC and ALG molecules. In vitro drug release studies at pH 7.4 and pH 9.0 exhibited that the release rate of BD was significantly decreased after ALG microspheres coating with CS and QAC. Moreover, ALG microspheres coated with QAC showed a prolonged release profile for BD at pH 9.0. Therefore, QAC/ALG microspheres may be a promising hydrophilic macromolecular drug carrier for a prolonged and sustained delivery. Full article
(This article belongs to the Special Issue Functionally Responsive Polymeric Materials)
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Open AccessArticle DNA Binding with Acetate Bis(1,10-phenanthroline)silver(I) Monohydrate in a Solution and Metallization of Formed Structures
Polymers 2017, 9(6), 211; doi:10.3390/polym9060211
Received: 31 March 2017 / Revised: 15 May 2017 / Accepted: 17 May 2017 / Published: 8 June 2017
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Abstract
The study of DNA interaction with the acetate bis(1,10-phenanthroline)silver(I) monohydrate in a solution is of interest both for understanding the mechanism of biological activity of silver compound and for forming ordered structures (DNA fibrils) that can be used to solve various problems in
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The study of DNA interaction with the acetate bis(1,10-phenanthroline)silver(I) monohydrate in a solution is of interest both for understanding the mechanism of biological activity of silver compound and for forming ordered structures (DNA fibrils) that can be used to solve various problems in the field of nanotechnology. The analysis of changing the DNA conformation (secondary structure, persistent length and volume effects) during the interaction by the methods of UV spectroscopy with the analysis of DNA melting, circular dichroism, viscosity, flow birefringence, AFM (atomic force microscopy) and SEM (scanning electron microscopy) was performed. The formation of two types of complexes was observed. At lower concentration of compound in DNA solution, silver atoms form the coordination bonds with a macromolecule, while the released phenanthroline ligands intercalate between DNA bases. When the concentration of the compound increases, the phenanthroline ligands form an ordered “layer” around the helix. The excess of silver compounds in the DNA solution (with more than five silver atoms per base pair), DNA precipitation is observed with the formation of long fibrils. It was shown that the binding of silver to DNA during the formation of complexes provides further metallization of the resulting structures with the aid of reducing agents; phenanthroline ligands influence the result of such metallization. Full article
(This article belongs to the Special Issue Bio-inspired and Bio-based Polymers)
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Open AccessArticle Multifunctional Polymer Nanoparticles for Dual Drug Release and Cancer Cell Targeting
Polymers 2017, 9(6), 213; doi:10.3390/polym9060213
Received: 19 May 2017 / Revised: 6 June 2017 / Accepted: 6 June 2017 / Published: 9 June 2017
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Abstract
Multifunctional polymer nanoparticles have been developed for cancer treatment because they could be easily designed to target cancer cells and to enhance therapeutic efficacy according to cancer hallmarks. In this study, we synthesized a pH-sensitive polymer, poly(methacrylic acid-co-histidine/doxorubicin/biotin) (HBD) in which
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Multifunctional polymer nanoparticles have been developed for cancer treatment because they could be easily designed to target cancer cells and to enhance therapeutic efficacy according to cancer hallmarks. In this study, we synthesized a pH-sensitive polymer, poly(methacrylic acid-co-histidine/doxorubicin/biotin) (HBD) in which doxorubicin (DOX) was conjugated by a hydrazone bond to encapsulate an immunotherapy drug, imiquimod (IMQ), to form dual cancer-targeting and dual drug-loaded nanoparticles. At low pH, polymeric nanoparticles could disrupt and simultaneously release DOX and IMQ. Our experimental results show that the nanoparticles exhibited pH-dependent drug release behavior and had an ability to target cancer cells via biotin and protonated histidine. Full article
(This article belongs to the Special Issue Functionally Responsive Polymeric Materials)
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Open AccessArticle Preparation and Chromatographic Application of β-Cyclodextrin Molecularly Imprinted Microspheres for Paeoniflorin
Polymers 2017, 9(6), 214; doi:10.3390/polym9060214
Received: 27 April 2017 / Revised: 3 June 2017 / Accepted: 7 June 2017 / Published: 9 June 2017
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Abstract
The application of molecular imprinting technology in the separation and purification of active ingredients in natural products was widely reported, but remains a challenge. Enrichment and separation are especially limited. A surface imprinting technique was reported to synthesize molecularly imprinted microspheres (MIMs) in
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The application of molecular imprinting technology in the separation and purification of active ingredients in natural products was widely reported, but remains a challenge. Enrichment and separation are especially limited. A surface imprinting technique was reported to synthesize molecularly imprinted microspheres (MIMs) in this article. With paeoniflorin (PF) as the template molecule, β-cyclodextrin (β-CD) and acrylamide (AA) as the functional monomers, and poly(glycidyl methacrylate, GMA) microspheres (PGMA) as the backing material. MIMs have been characterized by FTIR and FESEM. Adsorption experiments indicated the adsorption capacity of MIMs was superior to those comparative non-imprinted microspheres (NIMs) and the binding isotherm of MIMs was in good agreement with the two-site binding model. The baseline separation of PF and its structural analogue albiflorin (AF) were achieved on the new MIMs packed column. MIMs showed good affinity and efficiency for separation of PF and AF compared with those comparative NIMs. The approach of fabricating MIMs is simple, rapid, and inexpensive, and may shed new light on the application of MIMs as a liquid chromatography stationary phase to separate and analyze PF and AF from the Red peony root extracts. Full article
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Open AccessArticle Primary Hepatocytes Cultured on a Fiber-Embedded PDMS Chip to Study Drug Metabolism
Polymers 2017, 9(6), 215; doi:10.3390/polym9060215
Received: 27 April 2017 / Revised: 25 May 2017 / Accepted: 7 June 2017 / Published: 10 June 2017
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Abstract
In vitro drug screening using reliable and predictable liver models remains a challenge. The identification of an ideal biological substrate is essential to maintain hepatocyte functions during in vitro culture. Here, we developed a fiber-embedded polydimethylsiloxane (PDMS) chip to culture hepatocytes. Hepatocyte spheroids
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In vitro drug screening using reliable and predictable liver models remains a challenge. The identification of an ideal biological substrate is essential to maintain hepatocyte functions during in vitro culture. Here, we developed a fiber-embedded polydimethylsiloxane (PDMS) chip to culture hepatocytes. Hepatocyte spheroids formed in this device were subjected to different flow rates, of which a flow rate of 50 μL/min provided the optimal microenvironment for spheroid formation, maintained significantly higher rates of albumin and urea synthesis, yielded higher CYP3A1 (cytochrome P450 3A1) and CYP2C11 (cytochrome P450 2C11) enzyme activities for metabolism, and demonstrated higher expression levels of liver-specific genes. In vitro metabolism tests on tolbutamide and testosterone by hepatocytes indicated predicted clearance rates of 1.98 ± 0.43 and 40.80 ± 10.13 mL/min/kg, respectively, which showed a good in vitro–in vivo correspondence. These results indicate that this system provides a strategy for the construction of functional engineered liver tissue that can be used to study drug metabolism. Full article
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Open AccessArticle Block Copolymer Membranes from Polystyrene-b-poly(solketal methacrylate) (PS-b-PSMA) and Amphiphilic Polystyrene-b-poly(glyceryl methacrylate) (PS-b-PGMA)
Polymers 2017, 9(6), 216; doi:10.3390/polym9060216
Received: 1 May 2017 / Revised: 1 June 2017 / Accepted: 2 June 2017 / Published: 10 June 2017
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Abstract
In this paper; we compare double hydrophobic polystyrene-b-poly(solketal methacrylate) (PS-b-PSMA) and amphiphilic polystyrene-b-poly(glyceryl methacrylate) (PS-b-PGMA) diblock copolymer membranes which are prepared by combining the block copolymer self-assembly in solution with a non-solvent induced phase separation
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In this paper; we compare double hydrophobic polystyrene-b-poly(solketal methacrylate) (PS-b-PSMA) and amphiphilic polystyrene-b-poly(glyceryl methacrylate) (PS-b-PGMA) diblock copolymer membranes which are prepared by combining the block copolymer self-assembly in solution with a non-solvent induced phase separation (SNIPS). Diblock copolymers (i.e., PS-b-PSMA) were synthesized by sequential living anionic polymerization, whereas polystyrene-b-poly(glyceryl methacrylate) (PS-b-PGMA) were obtained by acid hydrolysis of the acetonide groups of the polysolketal methacrylate (PSMA) blocks into dihydroxyl groups (PGMA). Membrane structures and bulk morphologies were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM); respectively. The resulting PS-b-PGMA diblock copolymers produce an ordered hexagonal cylindrical pore structure during the SNIPS process, while membranes fabricated from the double hydrophobic (PS-b-PSMA) do not under similar experimental conditions. Membrane performance was evaluated by water flux and contact angle measurements. Full article
(This article belongs to the Special Issue Polymers and Block Copolymers at Interfaces and Surfaces)
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Open AccessArticle Electrowetting Performances of Novel Fluorinated Polymer Dielectric Layer Based on Poly(1H,1H,2H,2H-perfluoroctylmethacrylate) Nanoemulsion
Polymers 2017, 9(6), 217; doi:10.3390/polym9060217
Received: 6 May 2017 / Revised: 26 May 2017 / Accepted: 8 June 2017 / Published: 11 June 2017
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Abstract
In electrowetting devices, hydrophobic insulating layer, namely dielectric layer, is capable of reversibly switching surface wettability through applied electric field. It is critically important but limited by material defects in dielectricity, reversibility, film forming, adhesiveness, price and so on. To solve this key
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In electrowetting devices, hydrophobic insulating layer, namely dielectric layer, is capable of reversibly switching surface wettability through applied electric field. It is critically important but limited by material defects in dielectricity, reversibility, film forming, adhesiveness, price and so on. To solve this key problem, we introduced a novel fluorinated polyacrylate—poly(1H,1H,2H,2H-perfluoroctylmethacrylate (PFMA) to construct micron/submicron-scale dielectric layer via facile spray coating of nanoemulsion for replacing the most common Teflon AF series. All the results illustrated that, continuous and dense PFMA film with surface relief less than 20 nm was one-step fabricated at 110 °C, and exhibited much higher static water contact angle of 124°, contact angle variation of 42°, dielectric constant of about 2.6, and breakdown voltage of 210 V than Teflon AF 1600. Particularly, soft and highly compatible polyacrylate mainchain assigned five times much better adhesiveness than common adhesive tape, to PFMA layer. As a promising option, PFMA dielectric layer may further facilitate tremendous development of electrowetting performances and applications. Full article
(This article belongs to the Special Issue Polymers and Block Copolymers at Interfaces and Surfaces)
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Open AccessArticle Preparation of Stable Superhydrophobic Coatings on Wood Substrate Surfaces via Mussel-Inspired Polydopamine and Electroless Deposition Methods
Polymers 2017, 9(6), 218; doi:10.3390/polym9060218
Received: 11 May 2017 / Revised: 5 June 2017 / Accepted: 9 June 2017 / Published: 12 June 2017
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Abstract
Mussel-inspired polydopamine (PDA) chemistry and electroless deposition approaches were used to prepare stable superhydrophobic coatings on wood surfaces. The as-formed PDA coating on a wood surface exhibited a hierarchical micro/nano roughness structure, and functioned as an “adhesive layer” between the substrate and a
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Mussel-inspired polydopamine (PDA) chemistry and electroless deposition approaches were used to prepare stable superhydrophobic coatings on wood surfaces. The as-formed PDA coating on a wood surface exhibited a hierarchical micro/nano roughness structure, and functioned as an “adhesive layer” between the substrate and a metallic film by the metal chelating ability of the catechol moieties on PDA, allowing for the formation of a well-developed micro/nanostructure hierarchical roughness. Additionally, the coating acted as a stable bridge between the substrate and hydrophobic groups. The morphology and chemical components of the prepared superhydrophobic wood surfaces were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The PDA and octadecylamine (OA) modified surface showed excellent superhydrophobicity with a water contact angle (CA) of about 153° and a rolling angle (RA) of about 9°. The CA further increased to about 157° and RA reduced to about 5° with the Cu metallization. The superhydrophobic material exhibited outstanding stability in harsh conditions including ultraviolet aging, ultrasonic washing, strong acid-base and organic solvent immersion, and high-temperature water boiling. The results suggested that the PDA/OA layers were good enough to confer robust, degradation-resistant superhydrophobicity on wood substrates. The Cu metallization was likely unnecessary to provide significant improvements in superhydrophobic property. However, due to the amazing adhesive capacity of PDA, the electroless deposition technique may allow for a wide range of potential applications in biomimetic materials. Full article
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Open AccessArticle Electrochemical Polymerization of Hydroquinone on Graphite Felt as a Pseudocapacitive Material for Application in a Microbial Fuel Cell
Polymers 2017, 9(6), 220; doi:10.3390/polym9060220
Received: 18 April 2017 / Revised: 23 May 2017 / Accepted: 8 June 2017 / Published: 15 June 2017
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Abstract
Here we reported the use of electropolymerization to achieve the transformation of aqueous hydroquinone to solid-phase polyhydroquinone (PHQ) with pseudocapacitive characteristics, and the application of this redox-active product to shuttle electron transfer in the anode system of a microbial fuel cell (MFC). The
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Here we reported the use of electropolymerization to achieve the transformation of aqueous hydroquinone to solid-phase polyhydroquinone (PHQ) with pseudocapacitive characteristics, and the application of this redox-active product to shuttle electron transfer in the anode system of a microbial fuel cell (MFC). The microscopic and spectroscopic results showed that the treatment of the graphite felt (GF) substrate with acids was effective in improving the amounts of surface-bound oxygen-containing groups, enabling better adhesion of PHQ onto the GF surfaces. The electrochemical measurements indicated that the resulting PHQ–AGF (acid treated GF) possessed high pseudocapacitance due to the fast and reversible redox cycling between hydroquinone and benzoquinone. The MFC equipped with the PHQ–AGF anode achieved a maximum power density of 633.6 mW m−2, which was much higher than 368.2, 228.8, and 119.7 mW m−2 corresponding to the MFC with the reference PHQ–GF, AGF, and GF anodes, respectively. The increase in the power performance was attributed to the incorporation of the redox-active PHQ abundant in C–OH and C=O groups that were beneficial to the increased extracellular electron transfer and enhanced bacterial adhesion on the anode. Full article
(This article belongs to the Special Issue Conductive Polymers 2017)
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Open AccessArticle Influence of the Processing Parameters on the Fiber-Matrix-Interphase in Short Glass Fiber-Reinforced Thermoplastics
Polymers 2017, 9(6), 221; doi:10.3390/polym9060221
Received: 12 April 2017 / Revised: 7 June 2017 / Accepted: 8 June 2017 / Published: 13 June 2017
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Abstract
The interphase in short fiber thermoplastic composites is defined as a three-dimensional, several hundred nanometers-wide boundary region at the interface of fibers and the polymer matrix, exhibiting altered mechanical properties. This region is of key importance in the context of fiber-matrix adhesion and
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The interphase in short fiber thermoplastic composites is defined as a three-dimensional, several hundred nanometers-wide boundary region at the interface of fibers and the polymer matrix, exhibiting altered mechanical properties. This region is of key importance in the context of fiber-matrix adhesion and the associated mechanical strength of the composite material. An interphase formation is caused by morphological, as well as thermomechanical processes during cooling of the plastic melt close to the glass fibers. In this study, significant injection molding processing parameters are varied in order to investigate the influence on the formation of an interphase and the resulting mechanical properties of the composite. The geometry of the interphase is determined using nano-tribological techniques. In addition, the influence of the glass fiber sizing on the geometry of the interphase is examined. Tensile tests are used in order to determine the resulting mechanical properties of the produced short fiber composites. It is shown that the interphase width depends on the processing conditions and can be linked to the mechanical properties of the short fiber composite. Full article
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Open AccessArticle Reinforcement of Gelatin-Based Nanofilled Polymer Biocomposite by Crystalline Cellulose from Cotton for Advanced Wound Dressing Applications
Polymers 2017, 9(6), 222; doi:10.3390/polym9060222
Received: 7 April 2017 / Revised: 6 June 2017 / Accepted: 12 June 2017 / Published: 13 June 2017
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Abstract
This study is designed to extract crystalline cellulose from cotton and reinforcing gelatin film for biomedical applications, especially as a wound dressing material for its exceptional biocompatibility and bio-activity. Moreover, gelatin helps in wound healing and crystalline cellulose as additive can improve its
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This study is designed to extract crystalline cellulose from cotton and reinforcing gelatin film for biomedical applications, especially as a wound dressing material for its exceptional biocompatibility and bio-activity. Moreover, gelatin helps in wound healing and crystalline cellulose as additive can improve its properties. Crystalline cellulose was prepared through hydrolysis and the effects of crystalline cellulose loading on the morphology, mechanical properties, and water sensitivity of the nanocomposite were investigated by means of scanning electron microscopy, tensile strength testing, and water absorption testing. Developed biocomposite film showed homogeneous dispersion of crystalline cellulose within the gelatin matrix and strong interfacial adherence between the matrix and reinforcement. Samples were tested for biocompatibility and in vitro cytotoxicity and found to have excellent biocompatibility without having any cytotoxicity. In vivo wound healing study in an animal model showed 40% increased healing than the model dressed by conventional dressing. Full article
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Open AccessArticle Tannin-Based Copolymer Resins: Synthesis and Characterization by Solid State 13C NMR and FT-IR Spectroscopy
Polymers 2017, 9(6), 223; doi:10.3390/polym9060223
Received: 10 May 2017 / Revised: 9 June 2017 / Accepted: 11 June 2017 / Published: 13 June 2017
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Abstract
In recent years, the interest for bio-sources is rising exponentially and tannins extracts are one of the most interesting, easily-available, phenolic building blocks. The condensed tannins or proanthocyanidins are already known for their polymerization chemistry, which is the basis for several natural-based materials
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In recent years, the interest for bio-sources is rising exponentially and tannins extracts are one of the most interesting, easily-available, phenolic building blocks. The condensed tannins or proanthocyanidins are already known for their polymerization chemistry, which is the basis for several natural-based materials (e.g., adhesives, foams). In the present work we aim to observe the behavior of the extract of Acacia Mimosa (Acacia mearnsii) when reacted with several possible co-monomers at different relative amount, pH and temperature conditions. The more insoluble copolymers obtained with formaldehyde, hexamine, glyoxal, maleic anhydride, furfural and furfuryl alcohol were analyzed through solid state 13C NMR (Nuclear magnetic resonance) and FT-IR (Fourier Transform-Infrared) spectroscopy. The 13C NMR afforded the opportunity to detect: (i) aromatic substitutions and consequent poly-condensations for the majority of the hardeners studied; (ii) acylation for the maleic anhydride and also some; (iii) Diels–Alder arrangements for the furanic co-monomers; the FT-IR spectroscopy suggested that the formaldehyde and hexamine copolymers present a higher cross-linking degree. Full article
(This article belongs to the Special Issue Bio-inspired and Bio-based Polymers)
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Open AccessArticle Polyamidoamine (PAMAM) Dendrimers Modified with Cathepsin-B Cleavable Oligopeptides for Enhanced Gene Delivery
Polymers 2017, 9(6), 224; doi:10.3390/polym9060224
Received: 15 March 2017 / Revised: 4 June 2017 / Accepted: 12 June 2017 / Published: 14 June 2017
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Abstract
Because of the complex mechanisms mediating cancer onset, prognosis, and metastatic behavior, different therapeutic approaches targeting these mechanisms have been investigated. Recent advancements in nanocarrier-based drug and gene delivery methods have encouraged scientific groups to investigate various novel therapeutic techniques. In this study,
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Because of the complex mechanisms mediating cancer onset, prognosis, and metastatic behavior, different therapeutic approaches targeting these mechanisms have been investigated. Recent advancements in nanocarrier-based drug and gene delivery methods have encouraged scientific groups to investigate various novel therapeutic techniques. In this study, a poly(amidoamine) (PAMAM) polymer-based gene carrier containing the cathepsin B-enzyme sensitive sequence (glycine-phenylalanine-leucine-glycine, GFLG) was evaluated to determine transfection efficiency. Following the GFLG sequence, the surface of PAMAM generation 4 (G4) was conjugated with histidine (H) and arginine (R) for improved endosomal escape and cellular uptake, respectively. The successful synthesis of G4-GLFG-H-R was confirmed by 1H-nuclear magnetic resonance spectroscopy. The polyplex composed of G4-GLFG-H-R and pDNA was simulated by the enzyme cathepsin B and induced endosomal escape of pDNA, which was confirmed by gel electrophoresis. Compared with the G4 control, enzyme-sensitive G4-GLFG-H-R showed higher transfection efficiency and lower cytotoxicity in HeLa cells. These results demonstrated that G4-GLFG-H-R may be a highly potent and efficient carrier for gene therapy applications. Full article
(This article belongs to the Special Issue Polymers and Nanogels for Gene Therapy)
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Open AccessArticle Thiol-Ene Photo-Click Collagen-PEG Hydrogels: Impact of Water-Soluble Photoinitiators on Cell Viability, Gelation Kinetics and Rheological Properties
Polymers 2017, 9(6), 226; doi:10.3390/polym9060226
Received: 4 May 2017 / Revised: 6 June 2017 / Accepted: 9 June 2017 / Published: 14 June 2017
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Abstract
Thiol-ene photo-click hydrogels were prepared via step-growth polymerisation using thiol-functionalised type-I collagen and 8-arm poly(ethylene glycol) norbornene-terminated (PEG-NB), as a potential injectable regenerative device. Type-I collagen was thiol-functionalised by a ring opening reaction with 2-iminothiolane (2IT), whereby up to 80 Abs.% functionalisation and
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Thiol-ene photo-click hydrogels were prepared via step-growth polymerisation using thiol-functionalised type-I collagen and 8-arm poly(ethylene glycol) norbornene-terminated (PEG-NB), as a potential injectable regenerative device. Type-I collagen was thiol-functionalised by a ring opening reaction with 2-iminothiolane (2IT), whereby up to 80 Abs.% functionalisation and 90 RPN% triple helical preservation were recorded via 2,4,6-Trinitrobenzenesulfonic acid (TNBS) colorimetric assay and circular dichroism (CD). Type, i.e., either 2-Hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl-1-propanone (I2959) or lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP), and concentration of photoinitiator were varied to ensure minimal photoinitiator-induced cytotoxicity and to enable thiol-ene network formation of collagen-PEG mixtures. The viability of G292 cells following 24 h culture in photoinitiator-supplemented media was largely affected by the photoinitiator concentration, with I2959-supplemented media observed to induce higher toxic response (0.1 → 0.5% (w/v) I2959, cell survival: 62 → 2 Abs.%) compared to LAP-supplemented media (cell survival: 86 → 8 Abs.%). In line with the in vitro study, selected photoinitiator concentrations were used to prepare thiol-ene photo-click hydrogels. Gelation kinetics proved to be largely affected by the specific photoinitiator, with LAP-containing thiol-ene mixtures leading to significantly reduced complete gelation time (τ: 187 s) with respect to I2959-containing mixtures (τ: 1683 s). Other than the specific photoinitiator, the photoinitiator concentration was key to adjusting the hydrogel storage modulus (G’), whereby 15-fold G’ increase (232 → 3360 Pa) was observed in samples prepared with 0.5% (w/v) compared to 0.1% (w/v) LAP. Further thiol-ene formulations with 0.5% (w/v) LAP and varied content of PEG-NB were tested to prepare photo-click hydrogels with porous architecture, as well as tunable storage modulus (G’: 540–4810 Pa), gelation time (τ: 73–300 s) and swelling ratio (SR: 1530–2840 wt %). The photoinitiator-gelation-cytotoxicity relationships established in this study will be instrumental to the design of orthogonal collagen-based niches for regenerative medicine. Full article
(This article belongs to the Special Issue Hydrogels in Tissue Engineering and Regenerative Medicine)
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Open AccessArticle A Conjugated Polyelectrolyte with Pendant High Dense Short-Alkyl-Chain-Bridged Cationic Ions: Analyte-Induced Light-Up and Label-Free Fluorescent Sensing of Tumor Markers
Polymers 2017, 9(6), 227; doi:10.3390/polym9060227
Received: 11 May 2017 / Revised: 8 June 2017 / Accepted: 12 June 2017 / Published: 15 June 2017
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Abstract
A novel cationic water-soluble conjugated polyelectrolyte (CPE) of polyfluorene that contains 15% fraction of 2,1,3-benzothiadiazole (BT) units (PFC3NBT) has been obtained. PFC3NBT demonstrates intramolecular energy transfer from the fluorene segments to BT sites when negatively charged species (SDS or DNAs) are added, following
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A novel cationic water-soluble conjugated polyelectrolyte (CPE) of polyfluorene that contains 15% fraction of 2,1,3-benzothiadiazole (BT) units (PFC3NBT) has been obtained. PFC3NBT demonstrates intramolecular energy transfer from the fluorene segments to BT sites when negatively charged species (SDS or DNAs) are added, following by a shift in emission color from blue to green, has been developed. The high density of positive charges and pendent short alkyl chains of N-propyltrimethylammoniums endow PFC3NBT with high solubility and high fluorescence quantum efficiency of 33.6% in water. The fluorescence emission properties were investigated in the presence of adverse buffer solutions, different surfactants and DNA strands. Interesting fluorescence emission quenching at short wavelength and fluorescence resonance energy transfer (FRET) induced light-on at BT sites were observed and discussed in detail. Very different from previous reports, the fluorescence emission spectra transition happens with an enhancement of integrated fluorescent intensity. The analytes induced a light-up sensing system was studied with a PFC3NBT/SDS complex mode and confirmed with DNA/DNA-FAM sensing systems. More exciting preliminary results on label-free sensing of tumor markers were also reported by investigating the unique fluorescence response to 11 kinds of proteins. These results provide a new insight view for designing CPEs with light-up and label-free features for biomolecular sensing. Full article
(This article belongs to the Special Issue Polymers for Chemosensing)
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Open AccessArticle A Novel Heterogalactan from Antrodia camphorata and Anti-Angiogenic Activity of Its Sulfated Derivative
Polymers 2017, 9(6), 228; doi:10.3390/polym9060228
Received: 17 May 2017 / Revised: 7 June 2017 / Accepted: 10 June 2017 / Published: 16 June 2017
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Abstract
A heterogalactan, named ACW0, was extracted from Antrodia camphorata and purified by anion exchange and gel permeation chromatography. It was composed of galactose (94.98%), traces of mannose (2.41%), and fucose (2.61%), with its molecular weight estimated to be 13.5 k Da. The polysaccharide
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A heterogalactan, named ACW0, was extracted from Antrodia camphorata and purified by anion exchange and gel permeation chromatography. It was composed of galactose (94.98%), traces of mannose (2.41%), and fucose (2.61%), with its molecular weight estimated to be 13.5 k Da. The polysaccharide ACW0 was shown to be a mannofucogalactan with a backbone chain of α-d-1,6-linked Gal, attached by a non-reducing terminal α-d-Man and α-l-Fuc on C-2 of nearly every six α-d-1,6-linked Gal residues. A sulfated polysaccharide, ACW0-Sul was achieved by the chlorosulfonic acid-pyridine method. Compared with the native polysaccharide, ACW0-Sul could disrupt tube formation and migration as well as cell growth of human microvascular endothelial cells (HMEC-1) dose-dependently. Further studies revealed that phosphorylation of Extracellular Regulated Protein Kinases (Erk) and Focal Adhesion Kinase (FAK) were significantly inhibited by ACW0-Sul. These results suggested that ACW0-Sul could be a potent candidate for anti-angiogenic agent development. Full article
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Open AccessArticle Pattern Switching in Soft Cellular Structures and Hydrogel-Elastomer Composite Materials under Compression
Polymers 2017, 9(6), 229; doi:10.3390/polym9060229
Received: 8 May 2017 / Revised: 1 June 2017 / Accepted: 13 June 2017 / Published: 16 June 2017
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Abstract
It is well known that elastic instabilities induce pattern transformations when a soft cellular structure is compressed beyond critical limits. The nonlinear phenomena of pattern transformations make them a prime candidate for controlling macroscopic or microscopic deformation and auxetic properties of the material.
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It is well known that elastic instabilities induce pattern transformations when a soft cellular structure is compressed beyond critical limits. The nonlinear phenomena of pattern transformations make them a prime candidate for controlling macroscopic or microscopic deformation and auxetic properties of the material. In this present work, the novel mechanical properties of soft cellular structures and related hydrogel–elastomer composites are examined through experimental investigation and numerical simulations. We provide two reliable approaches for fabricating hydrogel–elastomer composites with rationally designed properties and transformed patterns, and demonstrate that different geometries of the repeat unit voids of the periodic pattern can be used to influence the global characteristics of the soft composite material. The experimental and numerical results indicate that the transformation event is dependent on the boundary conditions and material properties of matrix material for soft cellular structures; meanwhile, the deformation-triggered pattern of matrix material affects the pattern switching and mechanical properties of the hydrogel–elastomer material, thus providing future perspectives for optimal design, or serving as a fabrication suggestion of the new hydrogel–elastomer composite material. Full article
(This article belongs to the Special Issue Functionally Responsive Polymeric Materials)
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Open AccessArticle Effect of Preparation Methods on the Tensile, Morphology and Solar Energy Conversion Efficiency of RGO/PMMA Nanocomposites
Polymers 2017, 9(6), 230; doi:10.3390/polym9060230
Received: 1 May 2017 / Revised: 1 June 2017 / Accepted: 14 June 2017 / Published: 18 June 2017
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Abstract
In this study, reduced graphene oxide (RGO)/polymethyl methacrylate (PMMA) nanocomposites were prepared by employing in situ polymerization and solution blending methods. In terms of mechanical properties, RGO loading increased the Young’s modulus but decreased the elongation at break for RGO/PMMA nanocomposites. Tensile strength
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In this study, reduced graphene oxide (RGO)/polymethyl methacrylate (PMMA) nanocomposites were prepared by employing in situ polymerization and solution blending methods. In terms of mechanical properties, RGO loading increased the Young’s modulus but decreased the elongation at break for RGO/PMMA nanocomposites. Tensile strength for solution blended RGO/PMMA nanocomposites increased after adding 0.5 wt % RGO, which was attributed to the good dispersion of RGO in the nanocomposites as evidenced from SEM and TEM. Solar energy conversion efficiency measurement results showed that the optimum concentration of RGO in the RGO/PMMA nanocomposites was found to be 1.0 wt % in order to achieve the maximum solar energy conversion efficiency of 25%. In the present study, the solution blended nanocomposites exhibited better overall properties than in situ polymerized nanocomposites owing to the better dispersion of RGO in solution blending. These findings would contribute to future work in search of higher conversion efficiency using nanocomposites. Full article
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Open AccessArticle Synthesis of PNVP-Based Copolymers with Tunable Thermosensitivity by Sequential Reversible Addition–Fragmentation Chain Transfer Copolymerization and Ring-Opening Polymerization
Polymers 2017, 9(6), 231; doi:10.3390/polym9060231
Received: 18 May 2017 / Revised: 7 June 2017 / Accepted: 14 June 2017 / Published: 18 June 2017
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Abstract
Through the reversible addition–fragmentation chain transfer (RAFT) copolymerization of 3-ethyl-1-vinyl-2-pyrrolidone (C2NVP) and N-vinylpyrrolidone (NVP), a series of well-defined P(C2NVP-co-NVP) copolymers were synthesized (Mn = ca. 8000 to 16,000 and Mw/Mn <1.5)
[...] Read more.
Through the reversible addition–fragmentation chain transfer (RAFT) copolymerization of 3-ethyl-1-vinyl-2-pyrrolidone (C2NVP) and N-vinylpyrrolidone (NVP), a series of well-defined P(C2NVP-co-NVP) copolymers were synthesized (Mn = ca. 8000 to 16,000 and Mw/Mn <1.5) by using a difunctional chain transfer agent, S-(1-methyl-4-hydroxyethyl acetate) O-ethyl xanthate (MHEX). Copolymerizing kinetics and different monomer ratio in feeds were conducted to study the apparent monomer reaction rate and reactivity ratios of NVP and C2NVP, which indicated similar reaction rates and predominantly ideal random copolymers for the two monomers. The Tgs of the obtaining P(C2NVP-co-NVP) copolymers significantly corresponded to not only molecular weights MWs but also copolymer compositions. These copolymers presented characteristic lower critical solution temperatures (LCST) behavior. We then studied the cloud points (CPs) of the copolymers with varying MWs and compositions. With different MWs, the CPs were linearly decreased from ca. 51 to 45 °C. With different compositions, the CPs of the copolymers decreased from ca. 48 to 29 °C with C2NVP content (i.e., from 60.8 to 89.9 mol %). Fitting the CPs by the theoretical equation, the result illustrated that the introduction of more hydrophobic units of C2NVP suppressed the hydrophilic interaction between the polymer chain and water. We then successfully proceeded the chain extension through the ring-opening polymerization (ROP) of ε-caprolactone (CL) to the synthesis of a novel P(C2NVP-co-NVP)-b-PCL amphiphilic block copolymer (Mn,NMR = 14,730 and Mw/Mn = 1.59). The critical micelle concentration (CMC) of the block copolymer had a value of ca. 1.46 × 10−4 g/L. The block copolymer micelle was traced by dynamic light scattering (DLS), obtaining thermosensitive behaviors with a particle size of ca. 240 nm at 25 °C and ca. 140 nm at 55 °C, respectively. Full article
(This article belongs to the Special Issue Functionally Responsive Polymeric Materials)
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Open AccessArticle The Preparation and Characterization of Pyrolysis Bio-Oil-Resorcinol-Aldehyde Resin Cold-Set Adhesives for Wood Construction
Polymers 2017, 9(6), 232; doi:10.3390/polym9060232
Received: 28 April 2017 / Revised: 14 June 2017 / Accepted: 15 June 2017 / Published: 18 June 2017
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Abstract
Resorcinol-formaldehyde (RF) resin is a kind of excellent exterior-grade wood structural adhesive, which can be conveniently cold-set for various applications. In order to decrease the production cost, pyrolysis bio-oil from renewable bioresources was used to replace resorcinol to synthesize the bio-oil-resorcinol-aldehyde (BRF) resin.
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Resorcinol-formaldehyde (RF) resin is a kind of excellent exterior-grade wood structural adhesive, which can be conveniently cold-set for various applications. In order to decrease the production cost, pyrolysis bio-oil from renewable bioresources was used to replace resorcinol to synthesize the bio-oil-resorcinol-aldehyde (BRF) resin. The effect of replacing resorcinol with bio-oil on the properties, bonding performance, and characterization of resorcinol-aldehyde resin was comparatively investigated. A higher solid content and viscosity, albeit a lower shear strength, was found when the replacement ratio of bio-oil increased. The bonding performance of BRF with 10 and 20 wt % bio-oil was close to that of the pure RF resin. However, the trends of being less cross-linked, more easily decomposed, but more porous were found when the substitution ratio of bio-oil was higher than 20 wt %. Interestingly, it was found that the wood failure values of the BRF resins with bio-oil of no more than 20 wt % were slightly higher than that of the pure RF resin. On the whole, BRF resins with 20 wt % bio-oil is recommended as a wood structural adhesive, comprehensively considering the bio-oil substitution ratio and resin properties. The results obtained here showed that pyrolysis bio-oil is a promising green raw material for the production of RF resin with lower cost. Full article
(This article belongs to the collection Polymeric Adhesives)
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Open AccessArticle Photo-Induced Vertical Alignment of Liquid Crystals via In Situ Polymerization Initiated by Polyimide Containing Benzophenone
Polymers 2017, 9(6), 233; doi:10.3390/polym9060233
Received: 25 May 2017 / Revised: 15 June 2017 / Accepted: 16 June 2017 / Published: 18 June 2017
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Abstract
Vertical alignment of liquid crystal (LC) was achieved in an easy and effective way: in situ photopolymerization of dodecyl acrylate (DA) monomers initiated by polyimide based on 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and 3,3′-dimethyl-4,4′-diaminodiphenyl methane (BTDA-DMMDA PI). The alignment behavior and alignment stabilities were characterized by
[...] Read more.
Vertical alignment of liquid crystal (LC) was achieved in an easy and effective way: in situ photopolymerization of dodecyl acrylate (DA) monomers initiated by polyimide based on 3,3′,4,4′-benzophenonetetracarboxylic dianhydride and 3,3′-dimethyl-4,4′-diaminodiphenyl methane (BTDA-DMMDA PI). The alignment behavior and alignment stabilities were characterized by a polarizing optical microscope (POM), which showed a stable vertical alignment after 12 h of thermal treatment. The chemical structures, morphology, and water contact angles of alignment films peeled from LC cells with and without DA monomers were analyzed by means of a Fourier transform infrared spectrometer (FTIR), a scanning electron microscope (SEM), and a contact angle tester, separately. The results confirmed that the DA monomers underwent self-polymerization and grafting polymerization initiated by the BTDA-DMMDA PI under ultraviolet irradiation, which aggregated on the surfaces of PI films. The water contact angles of the alignment films were about 15° higher, indicating a relative lower surface energy. In conclusion, the vertical alignment of LC was introduced by the low surface free energy of PI films grafted with DA polymer and intermolecular interactions between LC and DA polymers. Full article
(This article belongs to the Special Issue Photo-Responsive Polymers)
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Open AccessArticle Morphology Development and Mechanical Properties Variation during Cold-Drawing of Polyethylene-Clay Nanocomposite Fibers
Polymers 2017, 9(6), 235; doi:10.3390/polym9060235
Received: 17 May 2017 / Revised: 8 June 2017 / Accepted: 15 June 2017 / Published: 20 June 2017
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Abstract
In this work, the influence of composition and cold-drawing on nano- and micro-scale morphology and tensile mechanical properties of PE/organoclay nanocomposite fibers was investigated. Nanocomposites were prepared by melt compounding in a twin-screw extruder, using a maleic anhydride grafted linear low density polyethylene
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In this work, the influence of composition and cold-drawing on nano- and micro-scale morphology and tensile mechanical properties of PE/organoclay nanocomposite fibers was investigated. Nanocomposites were prepared by melt compounding in a twin-screw extruder, using a maleic anhydride grafted linear low density polyethylene (LLDPE–g–MA) and an organomodified montmorillonite (Dellite 67G) at three different loadings (3, 5 and 10 wt %). Fibers were produced by a single-screw extruder and drawn at five draw ratios (DRs): 7.25, 10, 13.5, 16 and 19. All nanocomposites, characterized by XRD, SEM, TEM, and FT-IR techniques, showed an intercalated/exfoliated morphology. The study evidenced that the nanoclay presence significantly increases both elastic modulus (up to +115% for fibers containing 10 wt % of D67G) and drawability of as-spun nanocomposite fibers. Moreover, at fixed nanocomposite composition, the cold-drawing process increases fibers elastic modulus and tensile strength at increasing DRs. However, at high DRs, “face-to-edge” rearrangement phenomena of clay layers (i.e., clay layers tend to rotate and touch each other) arise in fibers at high nanoclay loadings. Finally, nanocomposite fibers show a lower diameter reduction during drawing, with respect to the plain system, and surface feature of adjustable roughness by controlling the composition and the drawing conditions. Full article
(This article belongs to the Special Issue Polymer Nanocomposites)
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Open AccessArticle Isothermal and Non-Isothermal Crystallization Studies of Long Chain Branched Polypropylene Containing Poly(ethylene-co-octene) under Quiescent and Shear Conditions
Polymers 2017, 9(6), 236; doi:10.3390/polym9060236
Received: 26 May 2017 / Revised: 15 June 2017 / Accepted: 16 June 2017 / Published: 20 June 2017
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Abstract
Isothermal and non-isothermal crystallization behaviours of the blends of long chain branched polypropylene (LCB PP) and poly(ethylene-co-octene) (PEOc) with different weight ratios were studied under quiescent and shear flow using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and rheological measurements.
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Isothermal and non-isothermal crystallization behaviours of the blends of long chain branched polypropylene (LCB PP) and poly(ethylene-co-octene) (PEOc) with different weight ratios were studied under quiescent and shear flow using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and rheological measurements. Experimental results showed that the crystallization of the LCB PP/PEOc blends were significantly accelerated due to the existence of the long chain branches (LCBs), the blends being able to rapidly crystallize even at 146 °C. The addition of PEOc that acts as a nucleating agent, could also increase the crystallization rate of LCB PP. However, the crystallization rate of LCB PP was reduced when the PEOc concentration was more than 60 wt %, showing a retarded crystallization growth mechanism. The morphology of the binary blend was changed from a sea-island structure to a co-continuous phase structure when the PEOc concentration was increased from 40 to 60 wt %. In comparison with linear isotactic iPP/PEOc, the interfacial tension between LCB PP and PEOc was increased. In addition, flow-induced crystallization of LCB PP/PEOc blends was observed. Possible crystallization mechanisms for both LCB PP/PEOc and iPP/PEOc blends were proposed. Full article
(This article belongs to the Special Issue Olefin Polymerization and Polyolefin)
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Open AccessArticle Design and Fabrication of Bilayer Hydrogel System with Self-Healing and Detachment Properties Achieved by Near-Infrared Irradiation
Polymers 2017, 9(6), 237; doi:10.3390/polym9060237
Received: 16 May 2017 / Revised: 15 June 2017 / Accepted: 16 June 2017 / Published: 20 June 2017
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Abstract
A novel kind of graphene oxide (GO)-containing bilayer hydrogel system with excellent self-healing and detachment properties stimulated by near-infrared irradiation is successively fabricated via a two-step in situ free radical polymerization. In addition to high mechanical strength, as components of a bilayer hydrogel
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A novel kind of graphene oxide (GO)-containing bilayer hydrogel system with excellent self-healing and detachment properties stimulated by near-infrared irradiation is successively fabricated via a two-step in situ free radical polymerization. In addition to high mechanical strength, as components of a bilayer hydrogel system, a poly N,N-dimethylacrylamide (PDMAA) layer with 3 mg/mL GO and a poly N-isopropylacrylamide (PNIPAm) layer with 3 mg/mL GO exhibits firm interface bonding. GO in a PDMAA layer transforms under a near-infrared laser into heat, which promotes mutual diffusion of hydrogen bonds and realizes a self-healing property. The irradiation of near infrared laser results in the temperature of PNIPAm layer being higher than the volume phase transition temperature, reducing the corresponding biological viscidity and achieving detachment property. The increase of GO content enhances the self-healing degree and detachment rate. The bilayer hydrogel system fabricated via mold design combines characteristics of PDMAA layer and PNIPAm layer, which can be treated as materials for medical dressings, soft actuators, and robots. Full article
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Open AccessCommunication A Near-Infrared Light-Responsive Hybrid Hydrogel Based on UCST Triblock Copolymer and Gold Nanorods
Polymers 2017, 9(6), 238; doi:10.3390/polym9060238
Received: 16 May 2017 / Revised: 13 June 2017 / Accepted: 17 June 2017 / Published: 20 June 2017
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Abstract
We report a near-infrared (NIR) light-responsive hydrogel that is capable of undergoing the gel to sol transition upon 785 nm light exposure based on a photothermal effect. The new hydrogel design relies on loading gold nanorods (AuNRs) in an ABA-type triblock copolymer, namely
[...] Read more.
We report a near-infrared (NIR) light-responsive hydrogel that is capable of undergoing the gel to sol transition upon 785 nm light exposure based on a photothermal effect. The new hydrogel design relies on loading gold nanorods (AuNRs) in an ABA-type triblock copolymer, namely P(AAm–co–AN)–b–PDMA–b–P(AAm–co–AN), where P(AAm–co–AN) stands for a random copolymer of acrylamide and acrylonitrile that exhibits an upper critical solution temperature (UCST) in aqueous solution and PDMA is water-soluble polydimethylacrylamide. At solution temperature below UCST, the insoluble P(AAm–co–AN) blocks lead to formation of hydrogel of flower-like micelles. When the hydrogel is exposed to 785 nm NIR light, the absorption due to the longitudinal surface plasmon resonance of loaded AuNRs generates heat that raises the hydrogel temperature above UCST and, consequently, the gel-to-sol transition. The NIR light-triggered release of a protein loaded in the hydrogel was found to display a switchable fashion. Full article
(This article belongs to the Special Issue Photo-Responsive Polymers)
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Open AccessArticle Preparation of Pendant Group-Functionalized Diblock Copolymers with Adjustable Thermogelling Behavior
Polymers 2017, 9(6), 239; doi:10.3390/polym9060239
Received: 9 May 2017 / Revised: 18 June 2017 / Accepted: 18 June 2017 / Published: 20 June 2017
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Abstract
Recently, several thermogelling materials have been developed for biomedical applications. In this study, we prepared methoxy polyethylene glycol (MPEG)-b-(poly(ε-caprolactone)-ran-poly(2-chloride-ε-caprolactone) (PCL-ran-PfCL)) (MP-Cl) diblock copolymers at room temperature via the ring-opening polymerization of caprolactone (CL)
[...] Read more.
Recently, several thermogelling materials have been developed for biomedical applications. In this study, we prepared methoxy polyethylene glycol (MPEG)-b-(poly(ε-caprolactone)-ran-poly(2-chloride-ε-caprolactone) (PCL-ran-PfCL)) (MP-Cl) diblock copolymers at room temperature via the ring-opening polymerization of caprolactone (CL) and 2-chloride-ε-caprolactone (fCL) monomers, using the terminal alcohol of MPEG as the initiator in the presence of HCl. MPEG-b-(poly(ε-caprolactone)-ran-poly(2-azide-ε-caprolactone) (PCL-ran-PCL-N3)) (MP-N3) was prepared by the reaction of MP-Cl with sodium azide. MPEG-b-(poly(ε-caprolactone)-ran-poly(2-amine-ε-caprolactone) (PCL-ran-PCL-NH2)) (MP-NH2) was subsequently prepared by Staudinger reaction. MP-Cl and MP-N3 showed negative zeta potentials, but MP-NH2 had a positive zeta potential. MP-Cl, MP-N3, and MP-NH2 solutions formed opaque emulsions at room temperature. The solutions exhibited a solution-to-hydrogel phase transition as a function of the temperature and were affected by variation of the chloride, azide, and the amine pendant group, as well as the amount of pendant groups present in their structure. Additionally, the phase transition of MP-Cl, MP-N3, and MP-NH2 copolymers was altered by pendant groups. The solution-to-hydrogel phase transition was adjusted by tailoring the crystallinity and hydrophobicity of the copolymers in aqueous solutions. Collectively, MP-Cl, MP-N3, and MP-NH2 with various pendant-group contents in the PCL segment showed a solution-to-hydrogel phase transition that depended on both the type of pendant groups and their content. Full article
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Open AccessArticle Controlled Light Cross-Linking Technique to Prepare Healable Materials
Polymers 2017, 9(6), 241; doi:10.3390/polym9060241
Received: 25 April 2017 / Revised: 19 June 2017 / Accepted: 19 June 2017 / Published: 21 June 2017
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Abstract
Detection of defects, damages and cracks in structural polymers is very difficult, and even if they are detected, they will be very hard to be repaired. This is because different kinds of stress can reduce the mechanical efficiency of structural and functional thermosetting
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Detection of defects, damages and cracks in structural polymers is very difficult, and even if they are detected, they will be very hard to be repaired. This is because different kinds of stress can reduce the mechanical efficiency of structural and functional thermosetting composite materials and they can damage the polymer matrix, thus reducing the purposed properties. General healing processes use thermal energy “alone” to heal these materials, thus impairing the intended properties of the materials. Therefore, we present a thermal healing ability that can be switched-on and/or -off at desire using illumination by photon energy (visible and ultra violet). By this technique, one can control local heal while keeping the efficiency of the material nearly unchanged. Furan-based cross-linker chemically reacts (forward- and reverse-reaction) with short-chains of maleimide-substituted poly(lauryl methacrylate) to form robust chemical bonds. This permits us to perform local control over thermally induced de- and/or re-cross-linking techniques. One can extend and apply this technique to cover micro-devices, coating-techniques, fine lithography, micro- and nano-fabrication processes, etc. Therefore, the present work developed a suitable technology with structural polymeric material, which has the ability to self-heal cracks (and damages) and recover structural function. Full article
(This article belongs to the collection Polymeric Adhesives)
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Open AccessReview Polyolefins, a Success Story
Polymers 2017, 9(6), 185; doi:10.3390/polym9060185
Received: 21 April 2017 / Revised: 19 May 2017 / Accepted: 21 May 2017 / Published: 24 May 2017
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Abstract
This paper reports the principal discoveries which have played a major role in the polyolefin field and have positioned polyolefins as the most produced plastics. The early development of polyolefins covering the production of LDPE (Low density polyethylene) at ICI (Imperial Chemical Industries)
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This paper reports the principal discoveries which have played a major role in the polyolefin field and have positioned polyolefins as the most produced plastics. The early development of polyolefins covering the production of LDPE (Low density polyethylene) at ICI (Imperial Chemical Industries) and the discovery of Phillips or Ziegler-Natta catalysts are highlighted in the first section. In the second part, the impact of the implementation of molecular catalysts on the research in polyolefins is discussed together with the most recent advances leading to high-performance tailor-made resins. Full article
(This article belongs to the Special Issue Tailored Polymer Synthesis by Advanced Polymerization Techniques)
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Open AccessReview Recent Progress on Hyperbranched Polymers Synthesized via Radical-Based Self-Condensing Vinyl Polymerization
Polymers 2017, 9(6), 188; doi:10.3390/polym9060188
Received: 5 May 2017 / Revised: 16 May 2017 / Accepted: 18 May 2017 / Published: 24 May 2017
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Abstract
This short review article summarizes recent reports on using controlled radical polymerization (CRP) of inimers (compounds containing initiating group and vinyl group in one molecule) or transmers (compounds containing chain transfer group and vinyl group in one molecule) for the synthesis of hyperbranched
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This short review article summarizes recent reports on using controlled radical polymerization (CRP) of inimers (compounds containing initiating group and vinyl group in one molecule) or transmers (compounds containing chain transfer group and vinyl group in one molecule) for the synthesis of hyperbranched polymers. These inimers and transmers that carry numerous functional groups could be homopolymerized, i.e., self-condensing vinyl polymerization, or copolymerized with monovinyl monomers, i.e., self-condensing vinyl copolymerization, using atom transfer radical polymerization (ATRP), nitroxide-mediated polymerization (NMP) or reversible addition fragmentation chain transfer (RAFT) polymerization techniques, producing hyperbranched polymers and hyperstar polymers with tunable molecular weights, compositions and degree of branching. Recent reports that attempted different strategies to regulate polymer–polymer reactions were introduced, demonstrating possible syntheses of hyperbranched polymers with better defined structures and relatively low molecular weight dispersity. Finally, several CRP-produced hyperbranched polymers were discussed on their applications for encapsulation of guest molecules, nanomedicine, diagnostic imaging and catalysis. Full article
(This article belongs to the Special Issue Functionally Responsive Polymeric Materials)
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Open AccessReview Poly(Lactic-co-Glycolic Acid): Applications and Future Prospects for Periodontal Tissue Regeneration
Polymers 2017, 9(6), 189; doi:10.3390/polym9060189
Received: 11 April 2017 / Revised: 8 May 2017 / Accepted: 11 May 2017 / Published: 1 June 2017
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Abstract
Periodontal tissue regeneration is the ultimate goal of the treatment for periodontitis-affected teeth. The success of regenerative modalities relies heavily on the utilization of appropriate biomaterials with specific properties. Poly (lactic-co-glycolic acid) (PLGA), a synthetic aliphatic polyester, has been actively investigated
[...] Read more.
Periodontal tissue regeneration is the ultimate goal of the treatment for periodontitis-affected teeth. The success of regenerative modalities relies heavily on the utilization of appropriate biomaterials with specific properties. Poly (lactic-co-glycolic acid) (PLGA), a synthetic aliphatic polyester, has been actively investigated for periodontal therapy due to its favorable mechanical properties, tunable degradation rates, and high biocompatibility. Despite the attractive characteristics, certain constraints associated with PLGA, in terms of its hydrophobicity and limited bioactivity, have led to the introduction of modification strategies that aimed to improve the biological performance of the polymer. Here, we summarize the features of the polymer and update views on progress of its applications as barrier membranes, bone grafts, and drug delivery carriers, which indicate that PLGA can be a good candidate material in the field of periodontal regenerative medicine. Full article
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Open AccessReview Phenylboronic Acid-Functionalized Layer-by-Layer Assemblies for Biomedical Applications
Polymers 2017, 9(6), 202; doi:10.3390/polym9060202
Received: 27 April 2017 / Revised: 26 May 2017 / Accepted: 29 May 2017 / Published: 31 May 2017
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Abstract
Recent progress in the development of phenylboronic acid (PBA)-functionalized layer-by-layer (LbL) assemblies and their biomedical applications was reviewed. Stimuli-sensitive LbL films and microcapsules that exhibit permeability changes or decompose in response to sugars and hydrogen peroxide (H2O2) have been
[...] Read more.
Recent progress in the development of phenylboronic acid (PBA)-functionalized layer-by-layer (LbL) assemblies and their biomedical applications was reviewed. Stimuli-sensitive LbL films and microcapsules that exhibit permeability changes or decompose in response to sugars and hydrogen peroxide (H2O2) have been developed using PBA-bearing polymers. The responses of PBA-modified LbL assemblies arise from the competitive binding of sugars to PBA in the films or oxidative decomposition of PBA by H2O2. Electrochemical glucose sensors have been fabricated by coating the surfaces of electrodes by PBA-modified LbL films, while colorimetric and fluorescence sensors can be prepared by modifying LbL films with boronic acid-modified dyes. In addition, PBA-modified LbL films and microcapsules have successfully been used in the construction of drug delivery systems (DDS). Among them, much effort has been devoted to the glucose-triggered insulin delivery systems, which are constructed by encapsulating insulin in PBA-modified LbL films and microcapsules. Insulin is released from the PBA-modified LbL assemblies upon the addition of glucose resulting from changes in the permeability of the films or decomposition of the film entity. Research into insulin DDS is currently focused on the development of high-performance devices that release insulin in response to diabetic levels of glucose (>10 mM) but remain stable at normal levels (~5 mM) under physiological conditions. Full article
(This article belongs to the Special Issue Advance of Polymers Applied to Biomedical Applications: Biointerface)
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Open AccessReview Micelles Formed by Polypeptide Containing Polymers Synthesized Via N-Carboxy Anhydrides and Their Application for Cancer Treatment
Polymers 2017, 9(6), 208; doi:10.3390/polym9060208
Received: 24 April 2017 / Revised: 26 May 2017 / Accepted: 30 May 2017 / Published: 4 June 2017
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Abstract
The development of multifunctional polymeric materials for biological applications is mainly guided by the goal of achieving the encapsulation of pharmaceutical compounds through a self-assembly process to form nanoconstructs that control the biodistribution of the active compounds, and therefore minimize systemic side effects.
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The development of multifunctional polymeric materials for biological applications is mainly guided by the goal of achieving the encapsulation of pharmaceutical compounds through a self-assembly process to form nanoconstructs that control the biodistribution of the active compounds, and therefore minimize systemic side effects. Micelles are formed from amphiphilic polymers in a selective solvent. In biological applications, micelles are formed in water, and their cores are loaded with hydrophobic pharmaceutics, where they are solubilized and are usually delivered through the blood compartment. Even though a large number of polymeric materials that form nanocarrier delivery systems has been investigated, a surprisingly small subset of these technologies has demonstrated potentially curative preclinical results, and fewer have progressed towards commercialization. One of the most promising classes of polymeric materials for drug delivery applications is polypeptides, which combine the properties of the conventional polymers with the 3D structure of natural proteins, i.e., α-helices and β-sheets. In this article, the synthetic pathways followed to develop well-defined polymeric micelles based on polypeptides prepared through ring-opening polymerization (ROP) of N-carboxy anhydrides are reviewed. Among these works, we focus on studies performed on micellar delivery systems to treat cancer. The review is limited to systems presented from 2000–2017. Full article
(This article belongs to the Special Issue Bio-inspired and Bio-based Polymers)
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Open AccessReview Role of Bio-Based Polymers on Improving Turbulent Flow Characteristics: Materials and Application
Polymers 2017, 9(6), 209; doi:10.3390/polym9060209
Received: 16 April 2017 / Revised: 19 May 2017 / Accepted: 30 May 2017 / Published: 6 June 2017
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Abstract
The remarkable ability of polymeric additives to reduce the level of frictional drag significantly in turbulent flow, even under extremely low dilutions, is known as turbulent drag-reduction behavior. Several bio-polymers have been assessed as promising drag-reducing agents for the potential replacement of high
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The remarkable ability of polymeric additives to reduce the level of frictional drag significantly in turbulent flow, even under extremely low dilutions, is known as turbulent drag-reduction behavior. Several bio-polymers have been assessed as promising drag-reducing agents for the potential replacement of high molecular weight synthetic polymers to improve safety and ameliorate environmental concerns. This article reviews the recent advances regarding the impact of several bio-polymer additives on turbulent drag reduction in either pipe or rotating disk flow systems, and their potential applications in the petroleum, biomedical, and agricultural industries. Full article
(This article belongs to the Special Issue Bio-inspired and Bio-based Polymers)
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Open AccessReview Control of Molecular Ordering, Alignment, and Charge Transport in Solution-Processed Conjugated Polymer Thin Films
Polymers 2017, 9(6), 212; doi:10.3390/polym9060212
Received: 27 April 2017 / Revised: 6 June 2017 / Accepted: 6 June 2017 / Published: 8 June 2017
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Abstract
Morphology of conjugated polymers is a critical factor that significantly affects intrinsic charge transport characteristics and in turn performance of polymer-based devices. Morphological defects including misaligned crystalline grains and grain boundaries significantly impede efficient charge hopping between transport sites, resulting in degradation of
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Morphology of conjugated polymers is a critical factor that significantly affects intrinsic charge transport characteristics and in turn performance of polymer-based devices. Morphological defects including misaligned crystalline grains and grain boundaries significantly impede efficient charge hopping between transport sites, resulting in degradation of device performance. Therefore, one important challenge is to control morphology of active polymer thin-films for achieving high performance flexible electronic devices. In the past decade, significant progress has been achieved in morphology control of conjugated polymer thin-films using solution-based processing techniques. This review focuses on recent advances in processing strategies that can tune the morphologies and thus impact charge transport properties of conjugated polymer thin films. Of the available processing strategies, polymer solution treatments and film deposition techniques will be mainly highlighted. The correlation between processing conditions, active layer morphologies, and device performance will be also be discussed. Full article
(This article belongs to the Special Issue Conductive Polymers 2017)
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Open AccessReview Catalytic Oxidation of Lignin in Solvent Systems for Production of Renewable Chemicals: A Review
Polymers 2017, 9(6), 240; doi:10.3390/polym9060240
Received: 5 May 2017 / Revised: 12 June 2017 / Accepted: 16 June 2017 / Published: 21 June 2017
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Abstract
Lignin as the most abundant source of aromatic chemicals in nature has attracted a great deal of attention in both academia and industry. Solvolysis is one of the promising methods to convert lignin to a number of petroleum-based aromatic chemicals. The process involving
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Lignin as the most abundant source of aromatic chemicals in nature has attracted a great deal of attention in both academia and industry. Solvolysis is one of the promising methods to convert lignin to a number of petroleum-based aromatic chemicals. The process involving the depolymerization of the lignin macromolecule and repolymerization of fragments is complicated influenced by heating methods, reaction conditions, presence of a catalyst and solvent systems. Recently, numerous investigations attempted unveiling the inherent mechanism of this process in order to promote the production of valuable aromatics. Oxidative solvolysis of lignin can produce a number of the functionalized monomeric or oligomeric chemicals. A number of research groups should be greatly appreciated with regard to their contributions on the following two concerns: (1) the cracking mechanism of inter-unit linkages during the oxidative solvolysis of lignin; and (2) the development of novel catalysts for oxidative solvolysis of lignin and their performance. Investigations on lignin oxidative solvolysis are extensively overviewed in this work, concerning the above issues and the way-forward for lignin refinery. Full article
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Open AccessErratum Erratum: pH Sensitive Hydrogels in Drug Delivery: Brief History, Properties, Swelling, and Release Mechanism, Material Selection and Applications. Polymers 2017, 9, 137
Polymers 2017, 9(6), 225; doi:10.3390/polym9060225
Received: 13 June 2017 / Accepted: 13 June 2017 / Published: 14 June 2017
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Abstract
The authors wish to make a change to their published paper [1]. [...]
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