Abstract In a reversible addition–fragmentation chain transfer (RAFT) polymerization, the chain-transfer agent (CTA) is selected to regulate the radical polymerization, although the specific functional group retained in an amphiphilic macromolecule may influence its self-assembly and colloidal behavior. This feature can be advantageously exploited to engineer polymer nanoparticles with programmable behavior. Here, the carboxylic group of a dodecyl trithiocarbonate CTA was linked to ethanolamine to introduce a hydroxyl functionality while converting the ionizable terminus into a neutral amide. The resulting dual-purpose CTA was used as an initiator in the ring-opening polymerization (ROP) of D,l-lactide and subsequently to mediate the RAFT copolymerization of di(ethylene glycol) methyl ether methacrylate (EG2MA) and N-isopropylacrylamide (NIPAM). The result is an amphiphilic macromolecule capable of self-assemblying forming nanoparticles (NPs) with a poly(lactic acid) (PLA) core and a thermoresponsive shell. Eight copolymers were synthesized by varying PLA length, EG2MA fraction, and overall thermoresponsive block length in a 23 factorial design. These same properties were benchmarked against a similar polymer library in which the biodegradable portion was obtained from a 2-hydroxyethyl methacrylate-g-PLA macromonomer copolymerized with the aforementioned thermoresponsive monomers in a two-step RAFT polymerization. The reference copolymers followed the size scaling expected for micelle-like core–shell assemblies, whereas CTA-directed nanoparticles exhibited a nonconventional dependence of size on polymer composition, lower dispersity, and near-neutral to weakly positive surface charge. These findings establish CTA functionalization as a molecular design strategy that transfers information from the polymerization junction to nanoparticle self-assembly, interfacial properties, and thermoresponsive behavior.
Abstract Mucus is a critical component of the human immune system, creating a barrier against pathogenic infections and providing an environment that supports beneficial microbial communities. Mucins, the glycoproteins that form complex gel networks in mucus, leverage complex, multivalent interactions to tune their physicochemical properties, which impact their interaction with both commensal and pathogenic microbes. Because of the diversity of roles that mucus plays in biological systems, mucins themselves are so varied that it is impossible to fully replicate them. This limitation has hindered our ability to study mucosal structure–function–property relationships in vitro, especially as they relate to pathogenesis, and to deploy mucins for therapeutic applications. To overcome these barriers, we have developed a tunable, scalable platform that mimics key physical properties of mucus, supporting the standardization of studies and the application of a mucus-inspired polymer as a drug-delivery vehicle. Inspired by biological mucin synthesis, we report a bottlebrush polymer hydrogel platform capable of mimicking the macromolecular structure and function of these glycoproteins via redox-responsive cross-links and glycan presentation. The mechanical properties of this hydrogel are tunable and can be matched to the viscoelasticity of the mucus from diverse sources. Furthermore, no inherent microbial cytotoxicity is observed, enabling this platform to support in vitro studies of pathogen transport and growth in mucus-like systems. The ease of synthesis, structural control, and tunability afforded by this hydrogel will enable previously inaccessible studies of the mucosal environment and rational design of biosimilar hydrogels to support human health.
Abstract Poly(indole-5-carboxylic acid) [poly(IN5CA)] was prepared by acid-assisted oxidative polymerization of the indole-5-carboxylic acid monomer in concentrated formic acid, using ammonium peroxodisulfate as the oxidant, at three monomer-to-oxidant ratios, and evaluated as a proof-of-concept sensing platform. MALDI-TOF mass spectrometry showed a dominant peak consistent with a cyclic trimer, together with a minor series of higher-mass peaks spaced at single monomer-unit intervals, indicating that a small fraction of the material extends as linear oligomers. Raman and ATR-FTIR spectroscopy confirmed oxidized conjugated segments. At the highest oxidant loading (1:1), ATR-FTIR revealed strong carboxylate (COO–) bands indicative of an additional, oxidant-induced transformation of the carboxylic acid groups; the intermediate 2:1 ratio was therefore selected, as it yielded oxidized conjugated oligomers without this transformation. X-ray diffraction showed the material to be predominantly amorphous, with a minor crystalline component attributed to a residual sulfate-based salt derived from the oxidant. The selected formulation remained stable within its UV–vis spectral envelope over 21 days, while fluorescence intensity showed a modest, nonmonotonic variation over the same period. Poly(IN5CA), immobilized as a drop-cast film on glassy-carbon electrodes, showed a concentration-dependent potentiometric response to the cationic surfactants CTAB and CHX, attributed to neutralization of the film’s negative surface charge. The CTAB slope (−21.2 mV/decade) was markedly sub-Nernstian for a monovalent cation, whereas the CHX slope (−29.2 mV/decade) closely approached the theoretical value expected for an effectively divalent cation. A potentiometric response to the heavy metal ions tested was not reproducible under the present conditions. In solution, the free polymer showed a fluorometric response to both surfactants and to Pb2+, Co2+, Ni2+, Fe2+, and Cu2+, with the direction and magnitude of the response varying by ion. A preliminary paper-based assay further confirmed that CTAB- and CHX-induced fluorescence changes remain detectable when poly(IN5CA) is immobilized on a solid support, though with a concentration dependence distinct from that observed in solution. This pattern of divergent, ion-specific responses across both transduction modes is consistent with a chemically interpretable fingerprint rather than selective behavior. Although drift correction, selectivity, reversibility, and validation in real matrices remain necessary, the results identify poly(IN5CA) as a promising low-cost material for sensor arrays, wastewater surveillance, disinfectant residue monitoring, and adaptive process control.
Abstract ABA triblock copolyesters based on poly(l-lactide) hard end blocks and a poly(ε-caprolactone-stat-lactide) soft midblock were synthesized by sequential ring-opening polymerization using either controlled solution polymerization procedures with purified monomers or a simplified one-pot bulk process employing technical-grade monomers. All materials exhibited typical thermoplastic elastomeric behavior, with elongations at break ranging from approximately 300% to nearly 1000%, together with efficient elastic recovery and pronounced hysteretic energy dissipation during cyclic deformation. As neat materials, the solution-synthesized triblock copolymers displayed the highest elastomeric performance, whereas the bulk-synthesized copolymer showed lower extensibility and tensile strength, reflecting its more heterogeneous molecular architecture. Unexpectedly, the opposite trend was observed in poly(lactic acid) (PLA) toughening. Despite its less outstanding elastomeric properties, the structurally heterogeneous copolymer obtained by the one-pot bulk process proved to be a significantly more effective toughening agent for commercial PLA than the structurally well-defined triblock copolymers prepared in solution. At 25 wt % copolymer loading, the elongation at break of poly(lactic acid) increased from approximately 4% to over 100% while maintaining a Young’s modulus of about 1 GPa, whereas the more regular triblock copolymers produced only limited improvements in ductility despite their superior mechanical performance as neat elastomers. Cryofracture SEM revealed markedly different deformation mechanisms in the corresponding blends, while DSC suggested comparable amorphous-phase miscibility but substantially different thermal evolution during solidification. WAXD further showed that the superior toughening efficiency cannot be simply correlated with the overall degree of crystallinity but is accompanied by distinct changes in the organization of the solid state. The combined evidence suggests that the heterogeneous molecular architecture generated under industrially relevant bulk polymerization conditions promotes the development of a solid-state morphology more favorable for stable plastic deformation of the PLA matrix. Finally, bulk depolymerization enables the recovery of the constituent monomers from both the neat copolyesters and PLA-based blends, supporting the chemical recyclability of these materials. Overall, this study shows that molecular heterogeneity, resulting from a less controlled polymerization process, can instead provide a functional advantage, offering a simplified and potentially scalable route toward recyclable thermoplastic elastomers and efficient PLA toughening agents.
Abstract Cyclic sulfur-containing monomers represent a promising class of comonomers for radical ring-opening polymerization, but only a limited number of examples have been reported to date. Here, the cyclic xanthate tert-butyl 2-thioxo-1,3-oxathiolane-5-carboxylate (Oxa) was synthesized from readily available tert-butyl acrylate via epoxidation and subsequent ring extension with carbon disulfide. While homopolymerization was not observed, efficient copolymerization with vinyl acetate yielded copolymers containing dithiocarbonate units in the polymer backbone. Reactivity ratio analysis revealed a preference for heteropropagation, enabling efficient incorporation of dithiocarbonate units with Oxa contents of up to 40 mol %, at which compositions the copolymers displayed a tendency toward an alternating microstructure. The resulting copolymers were highly transparent and colorless and exhibited molar masses and glass transition temperatures comparable to those of poly(vinyl acetate). The incorporated dithiocarbonate units enabled selective backbone cleavage by aminolysis, base-mediated hydrolysis, or oxidative degradation, whereas acidic conditions (0.5 M HCl) did not affect the polymers. Copolymers containing at least 25 mol % Oxa generated low-molar-mass degradation products, confirming the efficient incorporation of degradable units into the polymer chains. These results establish cyclic xanthates derived from a readily accessible acrylate precursor as a versatile platform for introducing chemically degradable dithiocarbonate functionalities into vinyl acetate-based polymers.
