Polymers

1082 KiB

Open AccessArticle

Loading of Two Related Metal-Organic Frameworks (MOFs), [Cu₂(bdc)₂(dabco)] and [Cu₂(ndc)₂(dabco)], with Ferrocene

by Romain Heck, Osama Shekhah, Olexandra Zybaylo, Peter G. Weidler, Frank Friedrich, Robert Maul, Wolfgang Wenzel and Christof Wöll

Polymers 2011, 3(3), 1565-1574; https://doi.org/10.3390/polym3031565 - 21 Sep 2011

Cited by 24 | Viewed by 11906

Abstract

We have studied the loading of two related, similar porous metal-organic frameworks (MOFs) [Cu₂(bdc)₂(dabco)] (1), and [Cu₂(ndc)₂(dabco)] (2) with ferrocene by exposing bulk powder samples to the corresponding vapor. On the [...] Read more.

We have studied the loading of two related, similar porous metal-organic frameworks (MOFs) [Cu₂(bdc)₂(dabco)] (1), and [Cu₂(ndc)₂(dabco)] (2) with ferrocene by exposing bulk powder samples to the corresponding vapor. On the basis of powder X-ray diffraction data and molecular dynamics (MD) calculations we propose that each pore can store one ferrocene molecule. Despite the rather pronounced similarity of the two MOFs a quite different behavior is observed, for 1 loading with ferrocene leads to an anisotropic 1% contraction, whereas for 2 no deformation is observed. Mössbauer spectroscopy studies reveal that the Fe oxidation level remains unchanged during the process. Time dependent studies reveal that the diffusion constant governing the loading from the gas-phase for 1 is approximately three times larger than the value for 2. Full article

(This article belongs to the Special Issue Coordination Polymers)

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631 KiB

Open AccessArticle

Polymeric Optical Code-Division Multiple-Access (CDMA) Encoder and Decoder Modules

by Xuejun Lu and Ray T. Chen

Polymers 2011, 3(3), 1554-1564; https://doi.org/10.3390/polym3031554 - 19 Sep 2011

Cited by 2 | Viewed by 7480

Abstract

We propose a low cost polymeric optical waveguides-based optical CDMA encoder and decoder modules. The structures of the optical CDMA encoder and decoder modules are presented. The performance of the optical CDMA encoder and decoder modules is simulated using 10-chip binary phase-shift keying [...] Read more.

We propose a low cost polymeric optical waveguides-based optical CDMA encoder and decoder modules. The structures of the optical CDMA encoder and decoder modules are presented. The performance of the optical CDMA encoder and decoder modules is simulated using 10-chip binary phase-shift keying (BPSK) coding schemes. The optical CDMA encoder and decoder modules can effectively transmit and recover optical CDMA data streams. The SNR of the received signal is analyzed and determined to be primarily from the cross correlation with other channels. Full article

(This article belongs to the Special Issue Polymers for Optical Applications)

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1302 KiB

Open AccessArticle

NMR Studies and Molecular Dynamic Simulation of Synthetic Dendritic Antigens

by Maria Isabel Montañez, Francisco Najera and Ezequiel Perez-Inestrosa

Polymers 2011, 3(3), 1533-1553; https://doi.org/10.3390/polym3031533 - 13 Sep 2011

Cited by 19 | Viewed by 8153

Abstract

A series of synthetic benzylpenicillinoylated dendrimers has been prepared using up to 4th generation PAMAM dendrimers. These nanoconjugates, as nanosized Dendritic Antigens, are useful in the diagnostic evaluation of drug allergy due to specific molecular recognition with the Human Immunological System (IgE). The [...] Read more.

A series of synthetic benzylpenicillinoylated dendrimers has been prepared using up to 4th generation PAMAM dendrimers. These nanoconjugates, as nanosized Dendritic Antigens, are useful in the diagnostic evaluation of drug allergy due to specific molecular recognition with the Human Immunological System (IgE). The morphology and dimensions of the conjugates coupled to the orientation of the peripheral benzylpenicillin residues in the dendrimers may play key roles in such molecular recognition processes. Herein, the characterization and conformation of these structures are studied by a detailed analysis of 1D (¹H and ¹³C NMR) and 2D NMR (¹H,¹H-NOESY) spectra. These dendrimers in explicit solvent were studied by the atomistic forcefield-based molecular dynamics. Structural properties such as shape, radius-of-gyration and distribution of the monomers will be discussed in relation to the experimental observations. Full article

(This article belongs to the Special Issue Dendrimers and Hyperbranched Polymers)

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477 KiB

Open AccessArticle

Activity and Mechanism of Antimicrobial Peptide-Mimetic Amphiphilic Polymethacrylate Derivatives

by Iva Sovadinova, Edmund F. Palermo, Michael Urban, Philomene Mpiga, Gregory A. Caputo and Kenichi Kuroda

Polymers 2011, 3(3), 1512-1532; https://doi.org/10.3390/polym3031512 - 13 Sep 2011

Cited by 82 | Viewed by 11314

Abstract

Cationic amphiphilic polymethacrylate derivatives (PMAs) have shown potential as a novel class of synthetic antimicrobials. A panel of PMAs with varied ratios of hydrophobic and cationic side chains were synthesized and tested for antimicrobial activity and mechanism of action. The PMAs are shown [...] Read more.

Cationic amphiphilic polymethacrylate derivatives (PMAs) have shown potential as a novel class of synthetic antimicrobials. A panel of PMAs with varied ratios of hydrophobic and cationic side chains were synthesized and tested for antimicrobial activity and mechanism of action. The PMAs are shown to be active against a panel of pathogenic bacteria, including a drug-resistant Staphylococcus aureus, compared to the natural antimicrobial peptide magainin which did not display any activity against the same strain. The selected PMAs with 47–63% of methyl groups in the side chains showed minimum inhibitory concentrations of ≤2–31 µg/mL, but cause only minimal harm to human red blood cells. The PMAs also exhibit rapid bactericidal kinetics. Culturing Escherichia coli in the presence of the PMAs did not exhibit any potential to develop resistance against the PMAs. The antibacterial activities of PMAs against E. coli and S. aureus were slightly reduced in the presence of physiological salts. The activity of PMAs showed bactericidal effects against E. coli and S. aureus in both exponential and stationary growth phases. These results demonstrate that PMAs are a new antimicrobial platform with no observed development of resistance in bacteria. In addition, the PMAs permeabilized the E. coli outer membrane at polymer concentrations lower than their MIC values, but they did not show any effect on the bacterial inner membrane. This indicates that mechanisms other than membrane permeabilization may be the primary factors determining their antimicrobial activity. Full article

(This article belongs to the Special Issue Antibacterial Polymers: From Natural Inspiration to Practical Applications)

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1891 KiB

Open AccessReview

An Excursion into the Intriguing World of Polymeric Tl(I) and Ag(I) Cyanoximates

by Nikolay Gerasimchuk

Polymers 2011, 3(3), 1475-1511; https://doi.org/10.3390/polym3031475 - 13 Sep 2011

Cited by 15 | Viewed by 9267

Abstract

The reaction of hot (~95 °C) aqueous solutions of Tl₂CO₃ with solid HL (HL = NC-C(=N-OH)-R is a cyanoxime, and R is an electron-withdrawing group; 37 ligands are known up-to-date) leads to crystalline yellow/orange TlL. Similarly, the reaction between AgNO [...] Read more.

The reaction of hot (~95 °C) aqueous solutions of Tl₂CO₃ with solid HL (HL = NC-C(=N-OH)-R is a cyanoxime, and R is an electron-withdrawing group; 37 ligands are known up-to-date) leads to crystalline yellow/orange TlL. Similarly, the reaction between AgNO₃ and ML (M = K⁺, Na⁺; L = anion of the monodeprotonated cyanoxime) this time at room temperature in mixed ethanol/aqueous solutions leads to sparingly soluble, colored AgL in high-yield. All synthesized monovalent Tl and Ag complexes were characterized using a variety of spectroscopic methods and X-ray analysis, which revealed the formation of primarily 2D coordination polymers of different complexity. In all cases cyanoxime mono-anions act as bridging ligands. Thallium(I) cyanoximates adopt in most cases a double-stranded motif that is originated from centrosymmetric (TlL)₂ dimers in which two Tl₂O₂ rhombs are fused into infinite “ladder-type” structure. There are very short (3.65–3.85 Å) intermetallic distances in (TlL)_n, which are close to that (3.46 Å) in metallic thallium. This opens the possibility for the electrochemical or chemical generation of mixed valence Tl(I)/Tl(III) polymers that may exhibit electrical conductivity. Synthesized silver(I) compounds demonstrate a very significant (for multiple years!) stability towards visible light. There are three areas of potential practical applications of these unusual complexes: (1) battery-less detectors of UV-radiation, (2) non electrical sensors for gases of industrial importance, (3) antimicrobial additives to light-curable acrylate polymeric glues, fillers and adhesives used during introduction of indwelling medical devices. Chemical, structural, technological and biological aspects of application of Tl(I) and Ag(I) cyanoximes-based coordination polymers are reviewed. Full article

(This article belongs to the Special Issue Coordination Polymers)

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1478 KiB

Open AccessArticle

A Molecular Antenna Coordination Polymer from Cadmium(II) and 4,4’-Bipyridine Featuring Three Distinct Polymer Strands in the Crystal

by Rüdiger W. Seidel, Richard Goddard, Bodo Zibrowius and Iris M. Oppel

Polymers 2011, 3(3), 1458-1474; https://doi.org/10.3390/polym3031458 - 5 Sep 2011

Cited by 11 | Viewed by 12281

Abstract

Reaction of cadmium perchlorate and the prototypical linear bridging ligand 4,4’-bipyridine (4,4’-bipy) in an ethanol/water mixture affords the one-dimensional coordination polymer, [{Cd(m-4,4’-bipy)(4,4’-bipy)₂(H₂O)₂}(ClO₄)₂× 2 4,4’-bipy × 4.5 H₂O]_n( [...] Read more.

Reaction of cadmium perchlorate and the prototypical linear bridging ligand 4,4’-bipyridine (4,4’-bipy) in an ethanol/water mixture affords the one-dimensional coordination polymer, [{Cd(m-4,4’-bipy)(4,4’-bipy)₂(H₂O)₂}(ClO₄)₂× 2 4,4’-bipy × 4.5 H₂O]_n(1). The Cd²⁺ ions adopt an octahedral coordination sphere and are joined into linear chains by 4,4’-bipy via two trans coordination sites. The remaining two trans sites in the equatorial plane carry terminally monodentate-bound 4,4’-bipy ligands, resulting in a molecular antenna arrangement. The two axial sites of each Cd²⁺ ion are occupied by aqua ligands. Compound 1 crystallizes in the non-centrosymmetric, monoclinic space group C2 with three similar, crystallographically independent, cationic coordination polymer strands in the unit cell, which essentially differ only in the conformations of the 4,4’-bipyridyl ligands. Consistent with the similarity of the local coordination environments of the three independent Cd atoms in the structure, ¹¹³Cd MAS NMR spectroscopy reveals a single resonance line at 89 ppm. Full article

(This article belongs to the Special Issue Coordination Polymers)

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Graphical abstract

997 KiB

Open AccessArticle

Photomechanical Response of Composite Structures Built from Azobenzene Liquid Crystal Polymer Networks

by Kyung Min Lee and Timothy J. White

Polymers 2011, 3(3), 1447-1457; https://doi.org/10.3390/polym3031447 - 2 Sep 2011

Cited by 30 | Viewed by 8794

Abstract

Optically directed shape adaptive responses have been sought after for many decades in photoresponsive polymeric materials. A number of recent examinations have elucidated elucidated the unique opportunities of photomechanical responses realized in azobenzene-functionalized liquid crystalline polymer networks (both elastomers and glasses). This work [...] Read more.

Optically directed shape adaptive responses have been sought after for many decades in photoresponsive polymeric materials. A number of recent examinations have elucidated elucidated the unique opportunities of photomechanical responses realized in azobenzene-functionalized liquid crystalline polymer networks (both elastomers and glasses). This work summarizes and contrasts the photomechanical response of glassy polydomain, monodomain, and twisted nematic azo-LCN materials to blue-green irradiation. Building from this summary, the combinatorial photomechanical response observed upon irradiation of composite cantilevers is examined. Large scale shape adaptations are realized, with novel responses that may be of potential use in future employment of these materials in actuation. Full article

(This article belongs to the Special Issue Liquid Crystalline Polymers)

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1570 KiB

Open AccessArticle

Microscopic and Spectroscopic Investigation of Poly(3-hexylthiophene) Interaction with Carbon Nanotubes

by Michele Giulianini, Eric R. Waclawik, John M. Bell, Manuela Scarselli, Paola Castrucci, Maurizio De Crescenzi and Nunzio Motta

Polymers 2011, 3(3), 1433-1446; https://doi.org/10.3390/polym3031433 - 29 Aug 2011

Cited by 34 | Viewed by 8811

Abstract

The inclusion of carbon nanotubes in polymer matrix has been proposed to enhance the polymer’s physical and electrical properties. In this study, microscopic and spectroscopic techniques are used to investigate the interaction between poly(3-hexylthiophene) (P3HT) and nanotubes and the reciprocal modification of physical [...] Read more.

The inclusion of carbon nanotubes in polymer matrix has been proposed to enhance the polymer’s physical and electrical properties. In this study, microscopic and spectroscopic techniques are used to investigate the interaction between poly(3-hexylthiophene) (P3HT) and nanotubes and the reciprocal modification of physical properties. The presence of P3HT-covered nanotubes dispersed in the polymer matrix has been observed by atomic force microscopy and transmission electron microscopy. Then, the modification of P3HT optical properties due to nanotube inclusion has been evidenced with spectroscopic techniques like absorption and Raman spectroscopy. The study is completed with detailed nanoscale analysis by scanning probe techniques. The ordered self assembly of polymer adhering on the nanotube is unveiled by showing an example of helical wrapping of P3HT. Scanning tunneling spectroscopy study provides information on the electronic structure of nanotube-polymer assembly, revealing the charge transfer from P3HT to the nanotube. Full article

(This article belongs to the Special Issue Carbon Nanotubes: Synthesis, Characterization and Applications)

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612 KiB

Open AccessArticle

Consolidation of Inorganic Precipitated Silica Gel

by Hussein Sahabi and Matthias Kind

Polymers 2011, 3(3), 1423-1432; https://doi.org/10.3390/polym3031423 - 29 Aug 2011

Cited by 8 | Viewed by 8794

Abstract

Colloidal gels are possible intermediates in the generation of highly porous particle systems. In the production process the gels are fragmented after their formation. These gel fragments compact to particles whose application-technological properties are determined by their size and porosity. In the case [...] Read more.

Colloidal gels are possible intermediates in the generation of highly porous particle systems. In the production process the gels are fragmented after their formation. These gel fragments compact to particles whose application-technological properties are determined by their size and porosity. In the case of precipitated silica gels, this consolidation process depends on temperature and pH, among other parameters. It is shown that these dependencies can be characterized by oedometer measurements. Originally, the oedometer test (one-dimensional compression test) stemmed from soil mechanics. It has proven to be an interesting novel examination method for gels. Quantitative data of the time-dependent shrinkage of gel samples can be obtained. The consolidation of the gels shows a characteristic dependence on the above parameters. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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778 KiB

Open AccessArticle

Synthesis of Stimuli-responsive, Water-soluble Poly[2-(dimethylamino)ethyl methacrylate/styrene] Statistical Copolymers by Nitroxide Mediated Polymerization

by Chi Zhang and Milan Maric

Polymers 2011, 3(3), 1398-1422; https://doi.org/10.3390/polym3031398 - 26 Aug 2011

Cited by 51 | Viewed by 14035

Abstract

2-(Dimethylamino)ethyl methacrylate/styrene statistical copolymers (poly(DMAEMA-stat-styrene)) with feed compositions f_DMAEMA = 80–95 mol%, (number average molecular weights M_n = 9.5–11.2 kg mol⁻¹) were synthesized using succinimidyl ester-functionalized BlocBuilder alkoxyamine initiator at 80 °C in bulk. Polymerization [...] Read more.

2-(Dimethylamino)ethyl methacrylate/styrene statistical copolymers (poly(DMAEMA-stat-styrene)) with feed compositions f_DMAEMA = 80–95 mol%, (number average molecular weights M_n = 9.5–11.2 kg mol⁻¹) were synthesized using succinimidyl ester-functionalized BlocBuilder alkoxyamine initiator at 80 °C in bulk. Polymerization rate increased three-fold on increasing f_DMAEMA = 80 to 95 mol%. Linear M_n increases with conversion were observed up to about 50% conversion and obtained copolymers possessed monomodal, relatively narrow molecular weight distributions (polydispersity = 1.32–1.59). Copolymers with f_DMAEMA = 80 and 90 mol% were also cleanly chain-extended with DMAEMA/styrene mixtures of 95 and 90 mol% DMAEMA, respectively, confirming the livingness of the copolymers. Copolymer phase behavior in aqueous solutions was examined by dynamic light scattering and UV-Vis spectroscopy. All copolymers exhibited lower critical solution temperature (LCST)-type behavior. LCST decreased with increasing styrene content in the copolymer and with increasing solution concentration. All copolymers were completely water-soluble and temperature insensitive at pH 4 but were more hydrophobic at pH 10, particularly copolymers with f_DMAEMA = 80 and 85 mol%, which were water-insoluble. At pH 10, LCST of copolymers with f_DMAEMA = 90 and 95 mol% were more than 10 °C lower compared to their solutions in neutral, de-ionized water. Block copolymers with two statistical blocks with different DMAEMA compositions exhibited a single LCST, suggesting the block segments were not distinct enough to exhibit separate LCSTs in water. Full article

(This article belongs to the Special Issue Water-Soluble Polymers)

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Graphical abstract

312 KiB

Open AccessReview

Poly Lactic-co-Glycolic Acid (PLGA) as Biodegradable Controlled Drug Delivery Carrier

by Hirenkumar K. Makadia and Steven J. Siegel

Polymers 2011, 3(3), 1377-1397; https://doi.org/10.3390/polym3031377 - 26 Aug 2011

Cited by 3401 | Viewed by 90753

Abstract

In past two decades poly lactic-co-glycolic acid (PLGA) has been among the most attractive polymeric candidates used to fabricate devices for drug delivery and tissue engineering applications. PLGA is biocompatible and biodegradable, exhibits a wide range of erosion times, has tunable mechanical properties [...] Read more.

In past two decades poly lactic-co-glycolic acid (PLGA) has been among the most attractive polymeric candidates used to fabricate devices for drug delivery and tissue engineering applications. PLGA is biocompatible and biodegradable, exhibits a wide range of erosion times, has tunable mechanical properties and most importantly, is a FDA approved polymer. In particular, PLGA has been extensively studied for the development of devices for controlled delivery of small molecule drugs, proteins and other macromolecules in commercial use and in research. This manuscript describes the various fabrication techniques for these devices and the factors affecting their degradation and drug release. Full article

(This article belongs to the Special Issue Bioinspired Polymers)

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634 KiB

Open AccessArticle

Influence of the Hydrophobicity of Polyelectrolytes on Polyelectrolyte Complex Formation and Complex Particle Structure and Shape

by Mandy Mende, Simona Schwarz, Stefan Zschoche, Gudrun Petzold and Andreas Janke

Polymers 2011, 3(3), 1363-1376; https://doi.org/10.3390/polym3031363 - 25 Aug 2011

Cited by 13 | Viewed by 7900

Abstract

Polyelectrolyte complexes (PECs) were prepared by structural uniform and strongly charged cationic and anionic modified alternating maleic anhydride copolymers. The hydrophobicity of the polyelectrolytes was changed by the comonomers (ethylene, isobutylene and styrene). Additionally, the n₋/n₊ ratio of the molar [...] Read more.

Polyelectrolyte complexes (PECs) were prepared by structural uniform and strongly charged cationic and anionic modified alternating maleic anhydride copolymers. The hydrophobicity of the polyelectrolytes was changed by the comonomers (ethylene, isobutylene and styrene). Additionally, the n₋/n₊ ratio of the molar charges of the polyelectrolytes and the procedure of formation were varied. The colloidal stability of the systems and the size, shape, and structure of the PEC particles were investigated by turbidimetry, dynamic light scattering (DLS) and atomic force microscopy (AFM). Dynamic light scattering indicates that beside large PEC particle aggregates distinct smaller particles were formed by the copolymers which have the highest hydrophobicity (styrene). These findings could be proved by AFM. Fractal dimension (D), root mean square (RMS) roughness and the surface profiles of the PEC particles adsorbed on mica allow the following conclusions: the higher the hydrophobicity of the polyelectrolytes, the broader is the particle size distribution and the minor is the swelling of the PEC particles. Hence, the most compact particles are formed with the very hydrophobic copolymer. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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3963 KiB

Open AccessArticle

Nanocomposites Based on Metal and Metal Sulfide Clusters Embedded in Polystyrene

by Gianfranco Carotenuto, Cinzia Giannini, Dritan Siliqi and Luigi Nicolais

Polymers 2011, 3(3), 1352-1362; https://doi.org/10.3390/polym3031352 - 22 Aug 2011

Cited by 6 | Viewed by 7720

Abstract

Transition-metal alkane-thiolates (i.e., organic salts with formula Me(SR)_x, where R is a linear aliphatic hydrocarbon group, –C_nH_2n+1) undergo a thermolysis reaction at moderately low temperatures (close to 200 °C), which produces metal atoms or metal [...] Read more.

Transition-metal alkane-thiolates (i.e., organic salts with formula Me(SR)_x, where R is a linear aliphatic hydrocarbon group, –C_nH_2n+1) undergo a thermolysis reaction at moderately low temperatures (close to 200 °C), which produces metal atoms or metal sulfide species and an organic by-product, disulfide (RSSR) or thioether (RSR) molecules, respectively. Alkane-thiolates are non-polar chemical compounds that dissolve in most techno-polymers and the resulting solid solutions can be annealed to generate polymer-embedded metal or metal sulfide clusters. Here, the preparation of silver and gold clusters embedded into amorphous polystyrene by thermolysis of a dodecyl-thiolate precursor is described in detail. However, this chemical approach is quite universal and a large variety of polymer-embedded metals or metal sulfides could be similarly prepared. Full article

(This article belongs to the Special Issue Polymer-Inorganic Hybrids and Their Applications)

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1100 KiB

Open AccessReview

Theory-Guided Design of Organic Electro-Optic Materials and Devices

by Larry Dalton and Stephanie Benight

Polymers 2011, 3(3), 1325-1351; https://doi.org/10.3390/polym3031325 - 19 Aug 2011

Cited by 59 | Viewed by 10604

Abstract

Integrated (multi-scale) quantum and statistical mechanical theoretical methods have guided the nano-engineering of controlled intermolecular electrostatic interactions for the dramatic improvement of acentric order and thus electro-optic activity of melt-processable organic polymer and dendrimer electro-optic materials. New measurement techniques have permitted quantitative determination [...] Read more.

Integrated (multi-scale) quantum and statistical mechanical theoretical methods have guided the nano-engineering of controlled intermolecular electrostatic interactions for the dramatic improvement of acentric order and thus electro-optic activity of melt-processable organic polymer and dendrimer electro-optic materials. New measurement techniques have permitted quantitative determination of the molecular order parameters, lattice dimensionality, and nanoscale viscoelasticity properties of these new soft matter materials and have facilitated comparison of theoretically-predicted structures and thermodynamic properties with experimentally-defined structures and properties. New processing protocols have permitted further enhancement of material properties and have facilitated the fabrication of complex device structures. The integration of organic electro-optic materials into silicon photonic, plasmonic, and metamaterial device architectures has led to impressive new performance metrics for a variety of technological applications. Full article

(This article belongs to the Special Issue Polymers for Optical Applications)

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1001 KiB

Open AccessArticle

Simplified Reflection Fabry-Perot Method for Determination of Electro-Optic Coefficients of Poled Polymer Thin Films

by Dong Hun Park, Jingdong Luo, Alex K.-Y. Jen and Warren N. Herman

Polymers 2011, 3(3), 1310-1324; https://doi.org/10.3390/polym3031310 - 18 Aug 2011

Cited by 11 | Viewed by 7814

Abstract

We report a simplified reflection mode Fabry-Perot interferometry method for determination of electro-optic (EO) coefficients of poled polymer thin films. Rather than fitting the detailed shape of the Fabry-Perot resonance curve, our simplification involves a technique to experimentally determine the voltage-induced shift in [...] Read more.

We report a simplified reflection mode Fabry-Perot interferometry method for determination of electro-optic (EO) coefficients of poled polymer thin films. Rather than fitting the detailed shape of the Fabry-Perot resonance curve, our simplification involves a technique to experimentally determine the voltage-induced shift in the angular position of the resonance minimum. Rigorous analysis based on optical properties of individual layers of the multilayer structure is not necessary in the data analysis. Although angle scans are involved, the experimental setup does not require a θ-2θ rotation stage and the simplified analysis is an advantage for polymer synthetic efforts requiring quick and reliable screening of new materials. Numerical and experimental results show that our proposed method can determine EO coefficients to within an error of ~8% if poled values for the refractive indices are used. Full article

(This article belongs to the Special Issue Polymers for Optical Applications)

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463 KiB

Open AccessArticle

Investigation of Second-Harmonic Generation and Molecular Orientation in Electrostatically Self-Assembled Thin Films

by Liangmin Zhang and Deliang Cui

Polymers 2011, 3(3), 1297-1309; https://doi.org/10.3390/polym3031297 - 18 Aug 2011

Cited by 1 | Viewed by 6313

Abstract

We report the observation and measurement of second-harmonic generation in self-assembled ultra thin film nonlinear optical materials using a femtosecond high repetition rate laser system. Second-harmonic intensity, as a function of the incident angle in these films, has been measured using incident p-polarized [...] Read more.

We report the observation and measurement of second-harmonic generation in self-assembled ultra thin film nonlinear optical materials using a femtosecond high repetition rate laser system. Second-harmonic intensity, as a function of the incident angle in these films, has been measured using incident p-polarized and s-polarized optical beam components. The second-order nonlinear optical susceptibilities of the thin films have also been determined. Using a curve fitting method and a crystal reference material, we have obtained second-order susceptibilities c₃₃₃ = 6.17 ± 0.18 pm/V and c₃₁₁ = 0.68 ± 0.02 pm/V at a fundamental wavelength of 1,200 nm. Based on linear molecular model approximation, we have also used the fitted data to investigate the average orientation distribution of the chromophore dipoles in the self-assembled film. The result indicates that the average tilt angle of the chromophore dipoles away from the substrate normal line is 25.2° ± 0.8°. Full article

(This article belongs to the Special Issue Polymers for Optical Applications)

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784 KiB

Open AccessArticle

Activity and Export of Engineered Nisin-(1-22) Analogs

by Annechien Plat, Anneke Kuipers, Jacobien G. de Lange, Gert N. Moll and Rick Rink

Polymers 2011, 3(3), 1282-1296; https://doi.org/10.3390/polym3031282 - 12 Aug 2011

Cited by 13 | Viewed by 7465

Abstract

The pentacyclic peptide antibiotic nisin, produced by Lactococcus lactis is ubiquitously applied as a food preservative. We previously demonstrated that the truncated nisin-(1-22) has only 10-fold lower activity than nisin. Here we aimed at further developing this tricyclic nisin analog to reach activity [...] Read more.

The pentacyclic peptide antibiotic nisin, produced by Lactococcus lactis is ubiquitously applied as a food preservative. We previously demonstrated that the truncated nisin-(1-22) has only 10-fold lower activity than nisin. Here we aimed at further developing this tricyclic nisin analog to reach activity comparable to that of nisin. Our data demonstrate that: (1) ring A has a large mutational freedom; (2) the composition of residues 20–22 strongly affects production levels of nisin-(1-22); (3) a positively charged C-terminus of nisin-(1-22) significantly enhances its antimicrobial activity; (4) nisin-(1-22) inhibits in vitro growth of a target strain using different dynamics than nisin. Full article

(This article belongs to the Special Issue Antibacterial Polymers: From Natural Inspiration to Practical Applications)

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Graphical abstract

192 KiB

Open AccessReview

Defensins: Potential Effectors in Autoimmune Rheumatic Disorders

by Stefan Vordenbäumen and Matthias Schneider

Polymers 2011, 3(3), 1268-1281; https://doi.org/10.3390/polym3031268 - 11 Aug 2011

Cited by 9 | Viewed by 7045

Abstract

Defensins are small cationic peptides with antimicrobial properties. They constitute a highly conserved innate immune defense mechanism across species. Based on the arrangement of disulfide-bonds, α- and β-defensins are distinguished in humans. Both types of defensin comprise several distinct molecules that are preferentially [...] Read more.

Defensins are small cationic peptides with antimicrobial properties. They constitute a highly conserved innate immune defense mechanism across species. Based on the arrangement of disulfide-bonds, α- and β-defensins are distinguished in humans. Both types of defensin comprise several distinct molecules that are preferentially expressed at epithelial surfaces and in blood cells. In the last decade, multiple immunomodulatory functions of defensins have been recognized, including chemotactic activity, the promotion of antigen presentation, and modulations of proinflammatory cytokine secretion. These findings suggested a role for defensins not only as a first line of defense, but also as connectors of innate and adaptive immune responses. Recently, increasingly accumulating evidence has indicated that defensins may also be involved in the pathogenesis of autoimmune rheumatic disorders such as systemic lupus erythematosus and rheumatoid arthritis. The current review summarizes the data connecting defensins to autoimmunity. Full article

(This article belongs to the Special Issue Antibacterial Polymers: From Natural Inspiration to Practical Applications)

223 KiB

Open AccessArticle

Spontaneous Vesicles Modulated by Polymers

by M. Mercedes Velázquez, Margarita Valero and Francisco Ortega

Polymers 2011, 3(3), 1255-1267; https://doi.org/10.3390/polym3031255 - 8 Aug 2011

Cited by 3 | Viewed by 6980

Abstract

Vesicles are widely used in technological applications including cosmetic products, in microencapsulation for drug delivery, as anticancer agents and in the technology of adhesives, paints and inks. The vesicle size and the surface charge are very important properties from a technological point of [...] Read more.

Vesicles are widely used in technological applications including cosmetic products, in microencapsulation for drug delivery, as anticancer agents and in the technology of adhesives, paints and inks. The vesicle size and the surface charge are very important properties from a technological point of view. Thus, the challenge in formulation is to find inexpensive stable vesicles with well-defined sizes and to modulate the surface charge of these aggregates. In this work we analyze the effect of different polymers on the structural properties of vesicles of the biodegradable surfactant sodium bis(2-ethyl-hexyl) sulfosuccinate, Aerosol OT. Using fluorescence, conductivity, electrophoretic mobility and dynamic light scattering measurements we study the effect of the polymer nature, molecular weight and polymer concentration on the stability and the vesicle size properties. Results demonstrate that it is possible to modulate both the size and the electric surface charge of spontaneous vesicles of Aerosol OT by the addition of very small percentages of poly(allylamine) and poly(maleic anhydride-alt-1-octadecen). Full article

(This article belongs to the Special Issue Water-Soluble Polymers)

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559 KiB

Open AccessArticle

Evaluation of the Biological Effects of Externally Tunable, Hydrogel Encapsulated Quantum Dot Nanospheres in Escherichia coli

by Somesree GhoshMitra, Tong Cai, David Diercks, Zhibing Hu, James Roberts, Jai Dahiya, Nathaniel Mills, DiAnna Hynds and Santaneel Ghosh

Polymers 2011, 3(3), 1243-1254; https://doi.org/10.3390/polym3031243 - 8 Aug 2011

Cited by 4 | Viewed by 8784

Abstract

Quantum Dots (QDs) have become an interesting subject of study for labeling and drug delivery in biomedical research due to their unique responses to external stimuli. In this paper, the biological effects of a novel hydrogel based QD nano-structure on E. coli bacteria [...] Read more.

Quantum Dots (QDs) have become an interesting subject of study for labeling and drug delivery in biomedical research due to their unique responses to external stimuli. In this paper, the biological effects of a novel hydrogel based QD nano-structure on E. coli bacteria are presented. The experimental evidence reveals that cadmium telluride (CdTe) QDs that are encapsulated inside biocompatible polymeric shells have reduced or negligible toxicity to this model cell system, even when exposed at higher dosages. Furthermore, a preliminary gene expression study indicates that QD-hydrogel nanospheres do not inhibit the Green Fluorescent Protein (GFP) gene expression. As the biocompatible and externally tunable polymer shells possess the capability to control the QD packing density at nanometer scales, the resulting luminescence efficiency of the nanostructures, besides reducing the cytotoxic potential, may be suitable for various biomedical applications. Full article

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1174 KiB

Open AccessReview

Thermoresponsive Polymers for Biomedical Applications

by Mark A. Ward and Theoni K. Georgiou

Polymers 2011, 3(3), 1215-1242; https://doi.org/10.3390/polym3031215 - 3 Aug 2011

Cited by 966 | Viewed by 64262

Abstract

Thermoresponsive polymers are a class of “smart” materials that have the ability to respond to a change in temperature; a property that makes them useful materials in a wide range of applications and consequently attracts much scientific interest. This review focuses mainly on [...] Read more.

Thermoresponsive polymers are a class of “smart” materials that have the ability to respond to a change in temperature; a property that makes them useful materials in a wide range of applications and consequently attracts much scientific interest. This review focuses mainly on the studies published over the last 10 years on the synthesis and use of thermoresponsive polymers for biomedical applications including drug delivery, tissue engineering and gene delivery. A summary of the main applications is given following the different studies on thermoresponsive polymers which are categorized based on their 3-dimensional structure; hydrogels, interpenetrating networks, micelles, crosslinked micelles, polymersomes, films and particles. Full article

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657 KiB

Open AccessArticle

Dark Antimicrobial Mechanisms of Cationic Phenylene Ethynylene Polymers and Oligomers against Escherichia coli

by Ying Wang, Zhijun Zhou, Jingshu Zhu, Yanli Tang, Taylor D. Canady, Eva Y. Chi, Kirk S. Schanze and David G. Whitten

Polymers 2011, 3(3), 1199-1214; https://doi.org/10.3390/polym3031199 - 29 Jul 2011

Cited by 43 | Viewed by 10865

Abstract

The interactions of poly(phenylene ethynylene) (PPE)-based cationic conjugated polyelectrolytes (CPEs) and oligo-phenylene ethynylenes (OPEs) with E. coli cells are investigated to gain insights into the differences in the dark killing mechanisms between CPEs and OPEs. A laboratory strain of E. coli with antibiotic [...] Read more.

The interactions of poly(phenylene ethynylene) (PPE)-based cationic conjugated polyelectrolytes (CPEs) and oligo-phenylene ethynylenes (OPEs) with E. coli cells are investigated to gain insights into the differences in the dark killing mechanisms between CPEs and OPEs. A laboratory strain of E. coli with antibiotic resistance is included in this work to study the influence of antibiotic resistance on the antimicrobial activity of the CPEs and OPEs. In agreement with our previous findings, these compounds can efficiently perturb the bacterial cell wall and cytoplasmic membrane, resulting in bacterial cell death. Electron microscopy imaging and cytoplasmic membrane permeability assays reveal that the oligomeric OPEs penetrate the bacterial outer membrane and interact efficiently with the bacterial cytoplasmic membrane. In contrast, the polymeric CPEs cause serious damage to the cell surface. In addition, the minimum inhibitory concentration (MIC) and hemolytic concentration (HC) of the CPEs and OPEs are also measured to compare their antimicrobial activities against two different strains of E. coli with the compounds’ toxicity levels against human red blood cells (RBC). MIC and HC measurements are in good agreement with our previous model membrane perturbation study, which reveals that the different membrane perturbation abilities of the CPEs and OPEs are in part responsible for their selectivity towards bacteria compared to mammalian cells. Our study gives insight to several structural features of the PPE-based CPEs and OPEs that modulate their antimicrobial properties and that these features can serve as a basis for further tuning their structures to optimize antimicrobial properties. Full article

(This article belongs to the Special Issue Antibacterial Polymers: From Natural Inspiration to Practical Applications)

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555 KiB

Open AccessArticle

Microspheres Containing Cibacron Blue F3G-A and Incorporated Iron Oxide Nanoparticles as Biomarker Harvesting Platforms

by Alexis Patanarut, Elissa H. Williams, Emanuel Petricoin, Lance A. Liotta and Barney Bishop

Polymers 2011, 3(3), 1181-1198; https://doi.org/10.3390/polym3031181 - 28 Jul 2011

Cited by 4 | Viewed by 9219

Abstract

In this work, magnetic functionality was introduced to cross-linked acrylamide-based particles via the in situ coprecipitation of iron oxide nanoparticles within the hydrogel particle interior. Cibacron Blue F3G-A was then incorporated onto the magnetic hydrogel scaffold to facilitate the harvest of targeted protein [...] Read more.

In this work, magnetic functionality was introduced to cross-linked acrylamide-based particles via the in situ coprecipitation of iron oxide nanoparticles within the hydrogel particle interior. Cibacron Blue F3G-A was then incorporated onto the magnetic hydrogel scaffold to facilitate the harvest of targeted protein species. The dye-loaded magnetic particles were physically characterized, and their protein sequestration performance was investigated. The results of these studies indicated that dye-loaded magnetic particles sequestered a greater amount of lower molecular weight proteins from the test solution than was achieved using reference particles, dye-loaded cross-linked N-isopropylacrylamide-based core-shell particles. This difference in protein harvesting ability may reflect the higher degree of dye-loading in the magnetic particles relative to the dye-loaded core-shell particles. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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272 KiB

Open AccessReview

Polymer-Optical-Fiber Lasers and Amplifiers Doped with Organic Dyes

by Jon Arrue, Felipe Jiménez, Igor Ayesta, M. Asunción Illarramendi and Joseba Zubia

Polymers 2011, 3(3), 1162-1180; https://doi.org/10.3390/polym3031162 - 25 Jul 2011

Cited by 62 | Viewed by 8904

Abstract

Polymer optical fibers (POFs) doped with organic dyes can be used to make efficient lasers and amplifiers due to the high gains achievable in short distances. This paper analyzes the peculiarities of light amplification in POFs through some experimental data and a computational [...] Read more.

Polymer optical fibers (POFs) doped with organic dyes can be used to make efficient lasers and amplifiers due to the high gains achievable in short distances. This paper analyzes the peculiarities of light amplification in POFs through some experimental data and a computational model capable of carrying out both power and spectral analyses. We investigate the emission spectral shifts and widths and on the optimum signal wavelength and pump power as functions of the fiber length, the fiber numerical aperture and the radial distribution of the dopant. Analyses for both step-index and graded-index POFs have been done. Full article

(This article belongs to the Special Issue Polymers for Optical Applications)

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4103 KiB

Open AccessArticle

Tunable Crystal-to-Crystal Phase Transition in a Cadmium Halide Chain Polymer

by Kevin Lamberts, Irmgard Kalf, Amr Ramadan, Paul Müller, Richard Dronskowski and Ulli Englert

Polymers 2011, 3(3), 1151-1161; https://doi.org/10.3390/polym3031151 - 25 Jul 2011

Cited by 17 | Viewed by 8566

Abstract

The chain polymer [{Cd(μ-X)₂py₂}¹_∞] (X = Cl, Br; py = pyridine) undergoes a fully reversible phase transition between a monoclinic low-temperature and an orthorhombic high-temperature phase. The transformation can be directly monitored in single crystals and [...] Read more.

The chain polymer [{Cd(μ-X)₂py₂}¹_∞] (X = Cl, Br; py = pyridine) undergoes a fully reversible phase transition between a monoclinic low-temperature and an orthorhombic high-temperature phase. The transformation can be directly monitored in single crystals and can be confirmed for the bulk by powder diffraction. The transition temperature can be adjusted by tuning the composition of the mixed-halide phase: Transition temperatures between 175 K up to the decomposition of the material at ca. 350 K are accessible. Elemental analysis, ion chromatography and site occupancy refinements from single-crystal X-ray diffraction agree with respect to the stoichiometric composition of the samples. Full article

(This article belongs to the Special Issue Coordination Polymers)

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689 KiB

Open AccessArticle

Towards Extrusion of Ionomers to Process Fuel Cell Membranes

by Yannick Molmeret, France Chabert, Nadia El Kissi, Cristina Iojoiu, Regis Mercier and Jean-Yves Sanchez

Polymers 2011, 3(3), 1126-1150; https://doi.org/10.3390/polym3031126 - 19 Jul 2011

Cited by 13 | Viewed by 8781

Abstract

While Proton Exchange Membrane Fuel Cell (PEMFC) membranes are currently prepared by film casting, this paper demonstrates the feasibility of extrusion, a solvent-free alternative process. Thanks to water-soluble process-aid plasticizers, duly selected, it was possible to extrude acidic and alkaline polysulfone ionomers. Additionally, [...] Read more.

While Proton Exchange Membrane Fuel Cell (PEMFC) membranes are currently prepared by film casting, this paper demonstrates the feasibility of extrusion, a solvent-free alternative process. Thanks to water-soluble process-aid plasticizers, duly selected, it was possible to extrude acidic and alkaline polysulfone ionomers. Additionally, the feasibility to extrude composites was demonstrated. The impact of the plasticizers on the melt viscosity was investigated. Following the extrusion, the plasticizers were fully removed in water. The extrusion was found to impact neither on the ionomer chains, nor on the performances of the membrane. This environmentally friendly process was successfully validated for a variety of high performance ionomers. Full article

(This article belongs to the Special Issue Conductive Polymers)

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Open AccessArticle

In Vitro and In Vivo Evaluation of a Folate-Targeted Copolymeric Submicrohydrogel Based on N-Isopropylacrylamide as 5-Fluorouracil Delivery System

by M. Dolores Blanco, Sandra Guerrero, Marta Benito, Ana Fernández, César Teijón, Rosa Olmo, Issa Katime and José M. Teijón

Polymers 2011, 3(3), 1107-1125; https://doi.org/10.3390/polym3031107 - 18 Jul 2011

Cited by 28 | Viewed by 10300

Abstract

Folate-targeted poly[(p-nitrophenyl acrylate)-co-(N-isopropylacrylamide)] nanohydrogel (F-SubMG) was loaded with 5-fluorouracil (5-FU) to obtain low (16.3 ± 1.9 μg 5-FU/mg F-SubMG) and high (46.8 ± 3.8 μg 5-FU/mg F-SubMG) load 5-FU-loaded F-SubMGs. The complete in vitro drug release took place in [...] Read more.

Folate-targeted poly[(p-nitrophenyl acrylate)-co-(N-isopropylacrylamide)] nanohydrogel (F-SubMG) was loaded with 5-fluorouracil (5-FU) to obtain low (16.3 ± 1.9 μg 5-FU/mg F-SubMG) and high (46.8 ± 3.8 μg 5-FU/mg F-SubMG) load 5-FU-loaded F-SubMGs. The complete in vitro drug release took place in 8 h. The cytotoxicity of unloaded F-SubMGs in MCF7 and HeLa cells was low; although it increased for high F-SubMG concentration. The administration of 10 μM 5-FU by 5-FU-loaded F-SubMGs was effective on both cellular types. Cell uptake of F-SubMGs took place in both cell types, but it was higher in HeLa cells because they are folate receptor positive. After subcutaneous administration (28 mg 5-FU/kg b.w.) in Wistar rats, F-SubMGs were detected at the site of injection under the skin. Histological studies indicated that the F-SubMGs were surrounded by connective tissue, without any signs of rejections, even 60 days after injection. Pharmacokinetic study showed an increase in MRT (mean residence time) of 5-FU when the drug was administered by drug-loaded F-SubMGs. Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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Open AccessArticle

Mechanical Properties and Adhesion of a Micro Structured Polymer Blend

by Brunero Cappella

Polymers 2011, 3(3), 1091-1106; https://doi.org/10.3390/polym3031091 - 15 Jul 2011

Cited by 22 | Viewed by 8135

Abstract

A 50:50 blend of polystyrene (PS) and poly(n-butyl methacrylate) (PnBMA) has been characterized with an Atomic Force Microscope (AFM) in Tapping Mode and with force-distance curves. The polymer solution has been spin-coated on a glass slide. PnBMA builds a uniform film on the [...] Read more.

A 50:50 blend of polystyrene (PS) and poly(n-butyl methacrylate) (PnBMA) has been characterized with an Atomic Force Microscope (AFM) in Tapping Mode and with force-distance curves. The polymer solution has been spin-coated on a glass slide. PnBMA builds a uniform film on the glass substrate with a thickness of @200 nm. On top of it, the PS builds an approximately 100 nm thick film. The PS-film undergoes dewetting, leading to the formation of holes surrounded by about 2 µm large rims. In those regions of the sample, where the distance between the holes is larger than about 4 µm, light depressions in the PS film can be observed. Topography, dissipated energy, adhesion, stiffness and elastic modulus have been measured on these three regions (PnBMA, PS in the rims and PS in the depressions). The two polymers can be distinguished in all images, since PnBMA has a higher adhesion and a smaller stiffness than PS, and hence a higher dissipated energy. Moreover, the polystyrene in the depressions shows a very high adhesion (approximately as high as PnBMA) and its stiffness is intermediate between that of PnBMA and that of PS in the rims. This is attributed to higher mobility of the PS chains in the depressions, which are precursors of new holes. Full article

(This article belongs to the Special Issue Polymer Thin Films and Membranes)

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328 KiB

Open AccessReview

Multimeric, Multifunctional Derivatives of Poly(ethylene glycol)

by Marina Zacchigna, Francesca Cateni, Sara Drioli and Gian Maria Bonora

Polymers 2011, 3(3), 1076-1090; https://doi.org/10.3390/polym3031076 - 13 Jul 2011

Cited by 29 | Viewed by 9874

Abstract

This article reviews the use of multifunctional polymers founded on high-molecular weight poly(ethylene glycol) (PEG). The design of new PEG derivatives assembled in a dendrimer-like multimeric fashion or bearing different functionalities on the same molecule is described. Their use as new drug delivery [...] Read more.

This article reviews the use of multifunctional polymers founded on high-molecular weight poly(ethylene glycol) (PEG). The design of new PEG derivatives assembled in a dendrimer-like multimeric fashion or bearing different functionalities on the same molecule is described. Their use as new drug delivery systems based on the conjugation of multiple copies or diversely active drugs on the same biocompatible support is illustrated. Full article

(This article belongs to the Special Issue Water-Soluble Polymers)

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252 KiB

Open AccessArticle

Thermal Cloud Point Fractionation of Poly(vinyl alcohol-co-vinyl acetate): Partition of Nanogels in the Fractions

by Leonard I. Atanase and Gérard Riess

Polymers 2011, 3(3), 1065-1075; https://doi.org/10.3390/polym3031065 - 4 Jul 2011

Cited by 12 | Viewed by 8684

Abstract

Poly(vinyl acetate-co-vinyl alcohol) (PVA), well-known as emulsion stabilizers, are obtained by partial hydrolysis of poly(vinyl acetate) (PVAc). Their thermal cloud point fractionation was performed in aqueous medium between 40 and 75 °C. This fractionation was carried out in order to get [...] Read more.

Poly(vinyl acetate-co-vinyl alcohol) (PVA), well-known as emulsion stabilizers, are obtained by partial hydrolysis of poly(vinyl acetate) (PVAc). Their thermal cloud point fractionation was performed in aqueous medium between 40 and 75 °C. This fractionation was carried out in order to get an insight in the partition of the initially present nanogels in the different fractions. All the fractions were characterized by size exclusion chromatography (SEC), NMR and dynamic light scattering (DLS) giving access to average degree of polymerization , DPw average degree of hydrolysis DH, average sequence lengths of vinyl acetate VAc, volume fraction and average size diameter (Dv) of nanogels and “free PVA chains”. The polydispersity of the samples in DPw, DH and VAc could be confirmed. The nanogels characterized by the highest values of volume fraction and Dv, in the range of 40–43 nm, were separated in the first coacervate fraction, whereas the most soluble fraction with low VAc content does not contain nanogels but only “free chains” of a Dv value of around 7–8 nm. The nanogels in the various fractions could further be disaggregated into “free chains” by complex formation with sodium dodecyl sulfate (SDS). Full article

(This article belongs to the Special Issue Polymer Nanogels and Microgels)

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Polymers, Volume 3, Issue 3 (September 2011) – 36 articles , Pages 975-1574

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