Search Results (33)

CO₂-responsive polymers have emerged as a significant class of smart materials, distinguished by their ability to reversibly alter their properties upon exposure to CO₂. Due to CO₂’s abundant availability, low cost, non-toxicity, energy efficiency, and excellent biocompatibility, these polymers offer remarkable environmental and practical advantages. This review succinctly explores recent advancements in the synthesis, mechanisms, and applications of CO₂-responsive polymers, emphasizing the pivotal roles of specific acidic and basic functional groups such as carboxylic acids, phenolic groups, amines, amidines, guanidines, and imidazoles. Advanced polymerization techniques including free radical polymerization (FRP), atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT), and nitroxide-mediated polymerization (NMP) are critically evaluated for their precision and flexibility in polymer design. Significant applications in smart separation, carbon capture, drug delivery, desalination, emulsions, tissue engineering, and sensing technologies are discussed comprehensively. Although substantial progress has been made, ongoing challenges include enhancing response speed, durability, sustainability, and economic viability. Future research is recommended to focus on innovative polymer structures, computational modeling, hybrid materials, and greener synthesis methods. This review aims to inspire continued exploration and practical utilization of CO₂-responsive polymers to address pressing environmental and technological needs. Full article

Fluorinated polymers are important materials in everyday life; however, most monomers of widely used fluoropolymers are gaseous, and their polymerization is difficult in an ordinary laboratory. Therefore, partially fluorinated polymers have recently been reported. As an easy-to-handle fluorine-containing monomer, α-trifluoromethylstyrene (TFMST) can be used to produce partially fluorinated polymers with trifluoromethyl groups in the main chain; however, TFMST does not homopolymerize, and there are limited reports on its copolymerization with styrene (ST). In this study, we applied the controlled radical polymerization method, which is effective for the polymerization of ST, to the copolymerization of TFMST and ST. We also showed that nitroxide-mediated polymerization is effective. The content ratio of TFMST in the TFMST–ST copolymer can be controlled between 10% and 40% by changing its monomer ratio. Additionally, the polymerization of TFMST and ST with substituents was performed to increase structural variations. The thermal stability as well as water and oil repellency of the synthesized polymers with different composition ratios and substituents were also evaluated. Full article

In this work, a commercial SBS was functionalized with the 2,2,6,6-tetramethylpiperidin-N-oxyl stable radical (TEMPO) via free-radical activation initiated with benzoyl peroxide (BPO). The obtained macroinitiator was used to graft both vinylbenzyl chloride (VBC) and styrene/VBC random copolymer chains from SBS to create g-VBC-x and g-VBC-x-co-Sty-z graft copolymers, respectively. The controlled nature of the polymerization as well as the use of a solvent allowed us to reduce the extent of the formation of the unwanted, non-grafted (co)polymer, thereby facilitating the graft copolymer’s purification. The obtained graft copolymers were used to prepare films via solution casting using chloroform. The –CH₂Cl functional groups of the VBC grafts were then quantitatively converted to –CH₂(CH₃)₃N⁺ quaternary ammonium groups via reaction with trimethylamine directly on the films, and the films, therefore, were investigated as anion exchange membranes (AEMs) for potential application in a water electrolyzer (WE). The membranes were extensively characterized to assess their thermal, mechanical, and ex situ electrochemical properties. They generally presented ionic conductivity comparable to or higher than that of a commercial benchmark as well as higher water uptake and hydrogen permeability. Interestingly, the styrene/VBC-grafted copolymer was found to be more mechanically resistant than the corresponding graft copolymer not containing the styrene component. For this reason, the copolymer g-VBC-5-co-Sty-16-Q with the best balance of mechanical, water uptake, and electrochemical properties was selected for a single-cell test in an AEM-WE. Full article

The kinetics of nitroxide-mediated dispersion copolymerization with crosslinking of styrene (STY) and divinylbenzene (DVB) in supercritical carbon dioxide (scCO₂) is addressed experimentally. 2,2,6,6-Tetramethylpiperidinyl-1-oxy (TEMPO) and dibenzoyl peroxide (BPO) were used as nitroxide controller and initiator, respectively. A high-pressure cell with lateral sapphire windows at 120 °C and 207 bar was used to carry out the polymerizations. The nitroxide-mediated homopolymerization (NMP) of STY, as well as the conventional radical copolymerization (FRC) of STY/DVB, at the same conditions were also carried out as reference and for comparison purposes. The effect of nitroxide content on polymerization rate, evolution of molecular weight averages, gel fraction, and swelling index was studied. Full article

A significantly improved thermal pyrolysis process for polystyrene (PS) is reported and mathematically modeled, including the description of the time evolution of the full molecular weight distribution of the polymer during its degradation by direct integration of the balance equations without simplifications. The process improves the styrene yield from 28–39%, reached in our previous report, to 58–75% by optimizing the heating ramp during the initial stage of the pyrolysis process. The process was tested at 390 and 420 °C on samples of conventional PS synthesized via free-radical polymerization (FRP) and PS with a nitroxide end-functionality synthesized via nitroxide mediated polymerization (NMP) with three levels of the nitroxide to initiator (N/I) molar ratio: 0.9, 1.1 and 1.3. The NMP-PS produced with N/I = 1.3 generates the highest styrene yield (75.2 ± 6.7%) with respect to the best FRP-PS yield (64.9 ± 1.2%), confirming the trends observed in our previous study. The mathematical model corrects some problems of a previous model that was based on assumptions that led to significant errors in the predictions; this is achieved by solving the full molecular weight distribution (MWD) without assumptions. The model provides further insight into the initial stages of the pyrolysis process which seem to be crucial to determine the chemical paths of the process and the styrene yield, as well as the influences of the initial heating ramp used and the presence of a nitroxide end-functionality in the polymer. Full article

Reversible-deactivation radical polymerization (RDRP) serves as a powerful tool nowadays for the preparations of unique linear and non-linear macromolecules. In this study, enhanced spin capturing polymerizations (ESCPs) of styrene (St) and tert-butyl acrylate (tBA) monomers were, respectively, conducted in the presence of difunctional (1Z,1′Z)-1,1′-(1,4-phenylene) bis (N-tert-butylmethanimine oxide) (PBBN) nitrone. Four-arm (PSt)₄ and (PtBA)₄ star macroinitiators (MIs) can be afforded. By correspondingly switching the second monomer (i.e., tBA and St), miktoarm star copolymers (μ-stars) of (PSt)₂-μ-(PtBA-b-PSt)₂ and (PtBA)₂-μ-(PSt-b-PtBA)₂) were thus obtained. We further conducted hydrolysis of the PtBA segments to PAA (i.e., poly(acrylic acid)) in μ-stars to afford amphiphilic μ-stars of (PSt)₂-μ-(PAA-b-PSt)₂ and (PAA)₂-μ-(PSt-b-PAA)₂. We investigated each polymerization step and characterized the obtained two sets of “sequence-isomeric” μ-stars by FT-IR, ¹H NMR, differential scanning calorimeter (DSC), and thermogravimetric analysis (TGA). Interestingly, we identified their physical property differences in the case of amphiphilic μ-stars by water contact angle (WCA) and atomic force microscopy (AFM) measurements. We thus proposed two microstructures caused by the difference of polymer chain sequences. Through this polymerization transformation (Ŧ) approach (i.e., ESCP-Ŧ-NMP), we demonstrated an interesting and facile strategy for the preparations of μ-stars with adjustable/switchable interior and exterior polymer structures toward the preparations of various nanomaterials. Full article

The aim of this contribution is to assess the use poly(styrene-co-glycidyl methacrylate-b-styrene) copolymers synthesized by nitroxide mediated polymerization (NMP) as chain extenders in the recycling of poly(lactic acid) biopolyester. Concisely, the addition of such block copolymers during the melt processing of recycled poly(lactic acid) (rPLA) leads to important increases in the viscosity average molecular weight of modified polymeric materials. Molar masses increase from 31,000 g/mol for rPLA to 48,000 g mol⁻¹ for the resulting rPLA/copolymer blends (bPLA). Fortuitously, this last value is nearly the same as the one for pristine PLA, which constitutes a first piece of evidence of the molar mass increase of the recycled biopolymer. Thermograms of chain extended rPLA show significant decreases in cold crystallization temperature and higher crystallinity degrees due to the chain extension process using NMP-synthesized copolymers. It was found that increasing epoxide content in the NMP-synthesized copolymers leads to increased degrees of crystallinity and lower cold crystallization temperatures. The rheological appraisal has shown that the addition of NMP synthesized copolymers markedly increases complex viscosity and elastic modulus of rPLA. Our results indicate that P(S-co-GMA)-b-S) copolymers act as efficient chain extenders of rPLA, likely due to the reaction between the epoxy groups present in P(S-co-GMA)-b-PS and the carboxyl acid groups present in rPLA. This reaction positively affects viscometric molar mass of PLA and its performance. Full article

Three alkoxyamines based on imidazoline radicals with a pyridine functional group—potential initiators of nitroxide-mediated, controlled radical polymerization—were synthesized. Electron Paramagnetic Resonance (EPR) measurements reveal biexponential kinetics for the thermolysis for diastereomeric alkoxyamines and monoexponential kinetics for an achiral alkoxyamine. For comparison, the thermolysis of all three alkoxyamines was studied by NMR in the presence of three different scavengers, namely tetramethylpiperidine-N-oxyl (TEMPO), thiophenol (PhSH), and β-mercaptoethanol (BME), and detailed analysis of products was performed. NMR differentiates between N-inversion, epimerization, and homolysis reactions. The choice of scavenger is crucial for making a reliable and accurate estimate of the true homolysis rate constant. Full article

Nitroxide-mediated polymerization is now a mature technique, at 35 years of age. During this time, several variants have been developed: electron spin capture polymerization (ESCP), photoNMP (NMP2), chemically initiated NMP (CI-NMP), spin label NMP (SL-NMP), and plasmon-initiated NMP (PI-NMP). This mini-review is devoted to the features and applications of these variants. Full article

A library of statistically random pentafluorostyrene (PFS) and methyl methacrylate (MMA) copolymers with narrow molecular weight distributions was produced, using nitroxide mediated polymerization (NMP) to study the effect of polymer composition on the performance of bottom-gate top-contact organic thin-film transistors, when utilized as the dielectric medium. Contact angle measurements confirmed the ability to tune the surface properties of copolymer thin films through variation of its PFS/MMA composition, while impedance spectroscopy determined the effect of this variation on dielectric properties. Bottom-gate, top-contact copper phthalocyanine (CuPc) based organic thin-film transistors were fabricated using the random copolymers as a dielectric layer. We found that increasing the PFS content led to increased field-effect mobility, until a point after which the CuPc no longer adhered to the polymer dielectric. Full article

Thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm)-based injectable hydrogels represent highly attractive materials in tissue engineering and drug/vaccine delivery but face the problem of long-term bioaccumulation due to non-degradability. In this context, we developed an amphiphilic poly(D,L-lactide)-b-poly(NIPAAm-co-polyethylene glycol methacrylate) (PLA-b-P(NIPAAm-co-PEGMA)) copolymer architecture, through a combination of ring-opening and nitroxide-mediated polymerizations, undergoing gelation in aqueous solution near 30 °C. Complete hydrogel mass loss was observed under physiological conditions after few days upon PLA hydrolysis. This was due to the inability of the resulting P(NIPAAm-co-PEGMA) segment, that contains sufficiently high PEG content, to gel. The copolymer was shown to be non-toxic on dendritic cells. These results thus provide a new way to engineer safe PNIPAAm-based injectable hydrogels with PNIPAAm-reduced content and a degradable feature. Full article

The thermal pyrolysis of polystyrene (PS) is gaining importance as the social pressure for achieving a circular economy is growing; moreover, the recovery of styrene monomer in such a process is especially relevant. In this study, a simple thermal pyrolysis process in the temperature range of 390–450 °C is developed. A working hypothesis is that by using a nitroxide-end functionalized PS (PS-T or dormant polymer), the initiation process for the production of monomer (unzipping) during the PS pyrolysis could be enhanced due to the tendency of the PS-T to activate at the nitroxide end. Two types of PS were used in this work, the first one was synthesized by free-radical polymerization (FRP-dead polymer) and the second by nitroxide-mediated polymerization (NMP) using three levels of nitroxide to initiator ratio: 1.3, 1.1, and 0.9. Analysis of the recovered products of the pyrolysis by gas-mass spectroscopy shows that the yield of styrene increases from ∼33% in the case of dead polymer to ∼38.5% for PS-T. A kinetic and mathematical model for the pyrolysis of dead and dormant polymer is proposed and solved by the method of moments. After a parameter sensitivity study and data fitting, the model is capable of explaining the main experimental trends observed. Full article

Nitroxide-mediated polymerization (NMP), (homo and block copolymerization with styrene (S) and butyl methacrylate/S) of ethylene glycol dicyclopentenyl ether (meth)acrylates (EGDEA and EGDEMA) was studied using BlocBuilder alkoxyamines. EGDEA homopolymerization was not well-controlled, independent of temperature (90–120 °C), or additional free nitroxide (0–10 mol%) used. Number average molecular weights (M_n) achieved for poly(EGDEA) were 4.0–9.5 kg mol⁻¹ and were accompanied by high dispersity (Ð = M_w/M_n = 1.62–2.09). Re-initiation and chain extension of the poly(EGDEA) chains with styrene (S) indicated some block copolymer formation, but a high fraction of chains were terminated irreversibly. EGDEA-stat-S statistical copolymerizations with a low mol fraction S in initial feed, f_S,0 = 0.05, were slightly better controlled compared to poly(EGDEA) homopolymerizations (Ð was reduced to 1.44 compared to 1.62 at similar conditions). EGDEMA, in contrast, was successfully polymerized using a small fraction of S (f_S,0 ~ 10 mol%) to high conversion (72%) to form well-defined EGDEMA-rich random copolymer (molar composition = F_EGDEMA = 0.87) of M_n = 14.3 kg mol⁻¹ and Ð = 1.38. EGDEMA-rich compositions were also polymerized with the unimolecular succinimidyl ester form of BlocBuilder initiator, NHS-BlocBuilder with similar results, although Ðs were higher ~1.6. Chain extensions resulted in monomodal shifts to higher molecular weights, indicating good chain end fidelity. Full article

Replacing petro-based materials with renewably sourced ones has clearly been applied to polymers, such as those derived from itaconic acid (IA) and its derivatives. Di-n-butyl itaconate (DBI) was (co)polymerized via nitroxide mediated polymerization (NMP) to impart elastomeric (rubber) properties. Homopolymerization of DBI by NMP was not possible, due to a stable adduct being formed. However, DBI/styrene (S) copolymerization by NMP at various initial molar feed compositions f_DBI,0 was polymerizable at different reaction temperatures (70–110 °C) in 1,4 dioxane solution. DBI/S copolymerizations largely obeyed first order kinetics for initial DBI compositions of 10% to 80%. Number-average molecular weight (M_n) versus conversion for various DBI/S copolymerizations however showed significant deviations from the theoretical M_n as a result of chain transfer reactions (that are more likely to occur at high temperatures) and/or the poor reactivity of DBI via an NMP mechanism. In order to suppress possible intramolecular chain transfer reactions, the copolymerization was performed at 70 °C and for a longer time (72 h) with f_DBI,0 = 50%–80%, and some slight improvements regarding the dispersity (Ð = 1.3–1.5), chain activity and conversion (~50%) were observed for the less DBI-rich compositions. The statistical copolymers produced showed a depression in T_g relative to poly(styrene) homopolymer, indicating the effect of DBI incorporation. Full article

Because alkoxyamines are employed in a number of important applications, such as nitroxide-mediated polymerization, radical chemistry, redox chemistry, and catalysis, research into their reactivity is especially important. Typically, the rate of alkoxyamine homolysis is strongly dependent on temperature. Nonetheless, thermal regulation of such reactions is not always optimal. This review describes various ways to reversibly change the rate of C–ON bond homolysis of alkoxyamines at constant temperature. The major methods influencing C–ON bond homolysis without alteration of temperature are protonation of functional groups in an alkoxyamine, formation of metal–alkoxyamine complexes, and chemical transformation of alkoxyamines. Depending on the structure of an alkoxyamine, these approaches can have a significant effect on the homolysis rate constant, by a factor of up to 30, and can shorten the half-lifetime from days to seconds. These methods open new prospects for the application of alkoxyamines in biology and increase the safety of (and control over) the nitroxide-mediated polymerization method. Full article