Chain Transfer Polymerization Research Articles

Toughening Healable Supramolecular Double Polymer Networks Based on Hydrogen Bonding and Metal Coordination.

Double polymer networks (DNs) consist of two interpenetrating polymer networks and can offer properties that are not merely a sum of the parts. Here, we report an elastic DN made from two supramolecular polymers (SMPs) that consist of the same poly(n-butyl acrylate) (BA) backbone. The two polymers feature different non-covalent binding motifs, which form dynamic, reversible cross-links. The polymers were prepared by reversible addi-ti-on-frag-mentation chain-transfer polymerization of n-butyl acrylate and either the self-complementary hydrogen-bonding motif 2-ureido-4[1H]pyri-mi-dinone, or the 2,6-bis(1'-methyl-benz--imidazolyl)-pyridine ligand, which forms complexes with metal ions. The supramolecular DN made by these components combines features of the single networks, including high thermal stability and resistance to creep. The DN further exhibits excellent healability and displays a higher extensibility and a higher toughness than its constituents. The mechanical characteristics of the DN can be further enhanced by selectively pre-stretching one of the networks, which is readily possible due to the reversible formation of the supramolecular cross-links and their orthogonal stimuli-responsive-ness.

Application of Sortase-Mediated Ligation for the Synthesis of Block Copolymers and Protein-Polymer Conjugates.

Sortase-mediated ligation (SML) has become a powerful tool for site-specific protein modification. However, sortaseA (SrtA) suffers from low catalytic efficiency and mediates an equilibrium reaction. Therefore, ligations with large macromolecules may be challenging. Here, the synthesis of polymeric building blocks for sortase-mediated ligation constituting peptide-polymers with either the recognition sequence for sortaseA (LPX1TGX2) or its nucleophilic counterpart (Gx) is demonstrated. The peptide-polymers are synthesized by solid-phase peptide synthesis followed by photo-iniferter (PI) reversible addition-fragmentation chain-transfer (RAFT) polymerization of various monomers. The building blocks are subsequently utilized to investigate possibilities and limitations when using macromolecules in SML. In particular, diblock copolymers are obtained even when using the orthogonal building blocks in equimolar ratio by exploiting a technique to shift the reaction equilibrium. However, ligations of two polymers can not be achieved when the degree of polymerization exceeds 100. Subsequently, C-terminal protein-polymer conjugates are synthesized. Several polymers are utilized that can replace the omnipresent polyethylene glycol (PEG) in future therapeutics. The conjugation is exemplified with a nanobody that is known for efficient neutralization of SARS-CoV-2. The study demonstrates a universal approach to polymer-LPX1TGX2 and Gx-polymer building blocks and gives insight into their application in SML.

Vinyl Ether Maleic Acid Polymers: Tunable Polymers for Self-Assembled Lipid Nanodiscs and Environments for Membrane Proteins.

Native lipid bilayer mimetics, including those that use amphiphilic polymers, are important for the effective study of membrane-bound peptides and proteins. Copolymers of vinyl ether monomers and maleic anhydride were developed with controlled molecular weights and hydrophobicity through reversible addition-fragmentation chain-transfer polymerization. After polymerization, the maleic anhydride units can be hydrolyzed, giving dicarboxylates. The vinyl ether and maleic anhydride copolymerized in a close to alternating manner, giving essentially alternating hydrophilic maleic acid units and hydrophobic vinyl ether units along the backbone after hydrolysis. The vinyl ether monomers and maleic acid polymers self-assembled with lipids, giving vinyl ether maleic acid lipid particles (VEMALPs) with tunable sizes controlled by either the vinyl ether hydrophobicity or the polymer molecular weight. These VEMALPs were able to support membrane-bound proteins and peptides, creating a new class of lipid bilayer mimetics.

Micelles of poly[oligo(ethylene glycol) methacrylate] as delivery vehicles for zinc phthalocyanine photosensitizers

Drug-loaded polymeric micelles have proven to be highly effective carrier systems for the efficient delivery of hydrophobic photosensitizers (PSs) in photodynamic therapy (PDT). This study introduces the micellization potential of poly(oligoethylene glycol methyl ether methacrylate) (pOEGMA) as a novel approach, utilizing the hydrophobic methacrylate segments of pOEGMA to interact with highly hydrophobic zinc phthalocyanine (ZnPc), thereby forming a potential micellar drug carrier system. The ZnPc molecule was synthesized from phthalonitrile derivatives and its fluorescence, photodegradation, and singlet oxygen quantum yields were determined in various solvents. In solvents such as tetrahydrofuran, dimethyl sulfoxide, and N,N-dimethylformamide, the ZnPc compound exhibited the requisite photophysical and photochemical properties for PDT applications. The pOEGMA homopolymer was synthesized via reversible addition-fragmentation chain-transfer polymerization, while ZnPc-loaded pOEGMA micelles were prepared using the nanoprecipitation method. Characterization of the pOEGMA, ZnPc, and micelles was conducted using FTIR,1H-NMR, dynamic light scattering, matrix-assisted laser desorption/ionization time-of-flight mass spectrometries, gel permeation chromatography, and transmission electron microscopy. The critical micelle concentration was determined to be 0.027 mg ml-1using fluorescence spectrometry. The drug loading and encapsulation efficiencies of the ZnPc-loaded micelles were calculated to be 0.67% and 0.47%, respectively. Additionally, the release performance of ZnPc from pOEGMA micelles was monitored over a period of nearly 10 d, while the lyophilized micelles exhibited stability for 3 months. Lastly, the ZnPc-loaded micelles were more biocompatible than ZnPc on L929 cell line. The results suggest that the pOEGMA homopolymer possesses the capability to micellize through its methacrylate segments when interacting with highly hydrophobic molecules, presenting a promising avenue for enhancing the delivery efficiency of hydrophobic PSs in PDT. Moreover, it was also deciphered that obtained formulations were highly biocompatible according to cytotoxicity results and could be safely employed as drug delivery systems in further applications.

Rh nanoparticles confined in triphenylphosphine oxide-functionalized core-crosslinked micelles with a polyanionic shell: Ynthesis, characterization, and application in aqueous biphasic hydrogenation

Core-crosslinked micelles (CCMs) with a hydrophilic polyanionic shell made of poly(sodium styrene sulfonate) chains, P(SS−Na+), a triphenylphosphine oxide-functionalized polystyrene core (TPPO@PSt) and crosslinked at the inner end of the polystyrene chains by diethylene glycol dimethacrylate (DEGDMA) were synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization as a stable TPPO@CCM-A latex. One-pot synthesis of rhodium nanoparticles (RhNPs) by the reduction of [Rh(COD)(μ-Cl)]2 in the aqueous TPPO@CCM-A latex yielded a stable RhNP-TPPO@CCM-A latex without the need of additional stabilizer or base. This Rh-loaded latex was applied to the catalytic biphasic hydrogenation of styrene under mild conditions with complete selectivity towards ethylbenzene and corrected turnover frequencies (cTOFs) ranging from 3250 to 10,010 h−1 based on the surface atoms of the RhNPs. Importantly, the catalytic phase proved recyclable after product extraction, owing to the efficient retention of the RhNPs by the core TPPO ligands.

Block Copolymers of Poly(N-Vinyl Pyrrolidone) and Poly(Vinyl Esters) Bearing n-alkyl Side Groups via Reversible Addition-Fragmentation Chain-Transfer Polymerization: Synthesis, Characterization, and Thermal Properties.

Amphiphilic block copolymers of N-vinyl pyrrolidone (NVP) and various vinyl esters (VEs), PNVP-b-PVEs, namely vinyl butyrate (VBu), vinyl decanoate (VDc), and vinyl stearate (VSt), were synthesized through RAFT polymerization techniques. The sequential addition of the monomers methodology was employed starting from the polymerization of NVP followed by the polymerization of the Ves' monomer. The polymerization of NVP was conducted at 60 °C in benzene solution using AIBN as the initiator and O-ethyl S-(phthalimidylmethyl) xanthate as the CTA. The resulting PNVP macro-CTA was further applied for the polymerization of the vinyl ester in dioxane solution at 80 °C using, again, AIBN as the initiator. The block copolymers were characterized through size-exclusion chromatography (SEC) and NMR spectroscopy. The thermal behavior of the copolymers was studied by Differential Scanning Calorimetry (DSC), whereas their thermal stability via Thermogravimetric Analysis (TGA) and Differential Thermogravimetry (DTG).

Data-Driven Design of Novel Polymer Excipients for Pharmaceutical Amorphous Solid Dispersions.

About 90% of active pharmaceutical ingredients (APIs) in the oral drug delivery system pipeline have poor aqueous solubility and low bioavailability. To address this problem, amorphous solid dispersions (ASDs) embed hydrophobic APIs within polymer excipients to prevent drug crystallization, improve solubility, and increase bioavailability. There are a limited number of commercial polymer excipients, and the structure-function relationships which lead to successful ASD formulations are not well-documented. There are, however, certain solid-state ASD characteristics that inform ASD performance. One characteristic shared by successful ASDs is a high glass transition temperature (Tg), which correlates with higher shelf stability and decreased drug crystallization. We aim to identify how polymer features such as side chain geometry, backbone methylation, and hydrophilic-lipophilic balance impact Tg to design copolymers capable of forming high-Tg ASDs. We tested a library of 50 ASD formulations (18 previously studied and 32 newly synthesized) of the model drug probucol with copolymers synthesized through automated photoinduced electron/energy transfer-reversible addition-fragmentation chain-transfer (PET-RAFT) polymerization. A machine learning (ML) algorithm was trained on the Tg data to identify the major factors influencing Tg, including backbone methylation and nonlinear side chain geometry. In both polymer alone and probucol-loaded ASDs, a Random Forest Regressor captured structure-function trends in the data set and accurately predicted Tg with an average R2 > 0.83 across a 10-fold cross validation. This ML model will be used to predict novel copolymers to design ASDs with high Tg, a crucial factor in predicting ASD success.

Changing the Linking Functionality in a Triblock Co-Polymer for Electrolyzer or Fuel Cell Membrane or Ionomer for Chemical Stability Improvements and Potentially Other Consequences.

We have developed a versatile scalable triblock polymer system for anion exchange membrane (AEM) based electrochemical energy conversion devices. This system is uniquely suited to solving both the membrane and ionomer challenges for the commercialization of AEM water electrolysis or fuel cells. Using our advanced fundamental understanding of AEMs based on our work which began in 2010, we can design systems from first principles to match the needs of the device. A triblock ABA polymer is readily fabricated that has both chemical and mechanical stability. The synthesis of these systems is robust, high yield and amenable to high volume production. It utilizes a novel dual chain transfer agent to mediate the chain-transfer ring-opening metathesis polymerization (ROMP) of cyclooctene (COE) or the polymerization of isoprene (IP) to give the hydrophobic B block of the polymer. This is followed by the reversible addition-fragmentation chain transfer radial polymerization of chloromethylstyrene (CMS). The polyCMS (pCMS) blocks are then quaternized with an amine to give the cationic hydrophilic A block. Before quaternization the B block is hydrogenated to give either semi-crystalline polyethylene (pE) or amorphous polymethylbutylene (pMB) from pCOE and pIP respectively. The obvious achilles heal in this system from a chemical durability standpoint is the linking ether functionality between the hydrophobic and hydrophilic blocks. The material we have synthesized to date have exceptional chemical and mechanical stability. It performs very well in ex-situ testing with KOH solutions and in device testing we have demonstrated >500 h at 50°C in water electrolysis in 5 cm2 cells in 1M carbonate electrolyte at 0.5 A cm-2. We attribute the chemical stability to the fact that we post quaternize the membrane to give methylpipiridinium cations and we assume that this reaction does not fully penetrate down the hydrophilic chain. This leaves a hydrophobic un-quaternized region close to the hydrophobic block that does not allow access to the ether linkage by the hydrated hydroxide anion. Recently a new approach to the telehelic mid block pCOE has been reported that has no ether linkages and allows the hydrophobic outer blocks to be linked by a methylene linker. This gives use an opportunity to directly contrast the chemical stability of two identical triblock co-polymers one with an ether linkage and one with a methylene linkage between blocks. In this presentation we will show the results from ex-situ chemical stability test one at low temperatures and higher hydroxide concentration and one at higher temperature and lower hydroxide concentration. There are many examples in polymer electrolyte chemistry where a simple change leads to unintended consequences. The geometry of the ether linkage versus the methylene linkage will change the way that the polymer chains will organize and entangle in ways that are not currently predictable. To probe the mechanical, chemical and morphological difference between these two polymers we will fully characterize and contrast both polymers physical chemical properties including water uptake, ionic conductivity, DSC, TGA, tensile strength and morphology through SAXS, WAXS and HRTEM. Data for the two polymer membranes will also be contrasted and compared in small laboratory 5 cm2 single cells for both electrolysis in dilute carbonate and H2/O2 fuel cells using conventional catalysts.

A phosphorus/fluorine‐containing block copolymer endows epoxy with multifunctionality

AbstractIn order to achieve flame retardant, hydrophobic, and toughened epoxy resins, phosphorus/fluorine‐containing block copolymer (FBCP) was synthesized by reversible addition‐fragmentation chain transfer polymerization, and then the as‐synthesized PMADOPO‐b‐PHFBA block copolymer was used as additive to modify the epoxy resin, accompanying with a random copolymer (FRCP) serving as control group. It showed that due to the regular arrangement of molecular chains, FBPC formed a fibrous‐like structure at the fracture interface of epoxy/PMADOPO‐b‐PHFBA (EP/FBCP) samples, effectively enhancing the toughness of epoxy composite materials. The fracture energy of EP90/FBCP‐10 was higher than that of EP90/FRCP‐10 and was about twice than that of pure EP. The addition of 3 wt% FBCP could enhance the limited oxygen index (LOI) of EP97/FBCP‐3 to 33.2% and reached a V‐1 UL‐94 rating. As the addition of FBCP increased, the LOI gradually increased. When the addition of FBCP was 10%, the LOI and UL‐94 of EP90/FBCP‐10 was 38.2% and V‐0 grade, respectively. Meanwhile, the presence of fluorine element effectively reduced the surface energy of the composite EP material. Compared with pure EP, the water contact angle of EP90/FBCP‐10 was about 101° with an increasing of 20.8%. Furthermore, the flame‐retardant mechanism of EP/FBCP epoxy composites was discussed.

Microphase Separation and Gelation through Polymerization-Induced Self-Assembly Using Star Polyethylene Glycols.

Polymerization-induced self-assembly (PISA) during the synthesis of diblock copolymers has garnered considerable interest; however, architectures beyond diblock copolymers have scarcely been explored. Here, we studied PISA using 4- and 8-arm star polyethylene glycol (PEG), as well as 2-arm (linear) PEG, wherein each terminus of PEG was functionalized with a chain-transfer agent, holding a constant molar mass for each arm. Styrene was polymerized from each PEG terminus through reversible addition-fragmentation chain-transfer (RAFT) polymerization in an ionic liquid (1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6]), with a total solute concentration of 40 wt %. While the styrene monomer is soluble in [BMIM][PF6], polystyrene is not; thus, self-assembly and cross-linking (gelation) occur. Structural analysis by small-angle X-ray scattering revealed that a relatively ordered microphase-separated structure for PISA was observed. Two-arm PEG-PS formed hexagonally packed cylinders, whereas 4- and 8-arm PEG-PS exhibited hexagonal close-packed spheres and disordered spheres. The dynamics, studied by oscillatory rheology, were also influenced by the number of arms; the 4-arm star block copolymers showed the highest plateau modulus. This study demonstrates that the topology is an important factor in controlling the microphase-separated structure and mechanical properties when preparing gels through PISA.

Nanosized Complexes of the Proteolytic Enzyme Serratiopeptidase with Cationic Block Copolymer Micelles Enhance the Proliferation and Migration of Human Cells.

In this study, we describe the preparation of the cationic block copolymer nanocarriers of the proteolytic enzyme serratiopeptidase (SER). Firstly, an amphiphilic poly(2-(dimethylamino)ethyl methacrylate)-b-poly(ε-caprolactone)-b-poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA9-b-PCL35-b-PDMAEMA9) triblock copolymer was synthesized by reversible addition-fragmentation chain-transfer (RAFT) polymerization. Then, cationic micellar nanocarriers consisting of a PCL hydrophobic core and a PDMAEMA hydrophilic shell were formed by the solvent evaporation method. SER was loaded into the polymeric micelles by electrostatic interaction between the positively charged micellar shell and the negatively charged enzyme molecules. The particle size, zeta potential, and colloid stability of complexes as a function of SER concentration were investigated by dynamic and electrophoretic light scattering. It was found that SER retained its proteolytic activity after immobilization in polymeric carriers. Moreover, the complexes have a concentration-dependent enhancing effect on the proliferation and migration of human keratinocyte HaCaT and gingival fibroblast HGF cells.

One‐Pot Catalytic Approaches: Building a New Toolbox for Macromolecular Design

AbstractOne‐pot processes have emerged as a powerful strategy in (macro)molecular synthesis: integrating a multicatalytic process maximizes efficiency, reduces waste, improves profitability, and provides versatile tools for designing of more sustainable processes without compromising selectivity and activity. This review article provides a critical overview of the application of one‐pot transformations in polymerization, with the goal of synthesizing polymers with tailored structures and functions for a wide range of applications. Recent advances in one‐pot polymerization techniques are highlighted, including examples from controlled polymerization methods such as atom transfer radical polymerization, reversible addition‐fragmentation chain transfer polymerization, and ring‐opening polymerization, among others. Special emphasis is placed on the design and optimization of reaction conditions, catalyst systems, and monomer combinations to achieve precise control over polymer structure and functionality.

Enhancing dye/salt separation efficiency through polysulfobetaine-modified poly (triazine imide)/polyethersulfone (PTI-PSBMA/PES) composite membrane fabrication

Membrane technology stands as a vital solution for efficient dye/salt separation in various industrial processes. For the first time in this study, polysulfobetaine-modified poly (triazine imide) (PTI-PSBMA) was simply prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization as an additive for PTI-PSBMA/PES composite membrane preparation using the phase inversion strategy. The SEM, AFM pictures, and WCA analysis results exhibited that the modified membranes with PTI-PSBMA possess smoother surfaces and are more hydrophilic. After conducting an investigation using a dead-end filtration setup, it has been determined that the PTIZ-1 membrane, containing 1.0 wt% of PTI-PSBMA, emerged as the most effective membrane. This membrane exhibited a remarkable water flux of 46.0 L. m−2 h−1 bar−1 and demonstrated the highest rejections for various dyes, such as Reactive Red 120 (92.3 %), Direct Yellow 29 (79.3 %), and Methyl Green (85.0 %). Additionally, the PTIZ-1 membrane displayed impressive antifouling properties, with protein adsorption decreasing by over 96.0 %. With exceptional rejection rates for dyes and high permeability for salts, this composite membrane presents a promising solution for practical applications in wastewater treatment and dye removal processes. This research contributes to advancing membrane technology by introducing a highly efficient composite membrane with enhanced separation properties, addressing critical challenges in industrial dye/salt separation processes.

BaTiO3 Catalyzed Ultrasonic-Driven Piezoelectric-Induced Reversible Addition-Fragmentation Chain-Transfer Polymerization in Aqueous Media.

Compared with normal stimulus such as light and heat, ultrasonic possesses much deeper penetration into tissues and organs and has lower scattering in heterogeneous systems as a noninvasive stimulus. Reversible addition-fragmentation chain-transfer polymerization (RAFT) in aqueous media is performed in a commercial ultrasonic wash bath with 40kHz frequency ultrasonic, in the presence of piezoelectric tetragonal BaTiO3 (BTO) nanoparticles. Owing to the electron transfer from BTO under the ultrasonic action, the water can be decomposed to produce hydroxyl radical (HO•) and initiate the RAFT polymerization (piezo-RAFT). The piezo-RAFT polymerization exhibits features of controllable and livingness, such as linear increase of molar mass and narrow molar mass distributions (Mw/Mn < 1.20). Excellent temporal control of the polymerization and the chain fidelity of polymers are illustrated by "ON and OFF" experiment and chain extension, separately. Moreover, this ultrasonic-driven piezoelectric-induced RAFT polymerization in aqueous media can be directly used for the preparation of piezoelectric hydrogel which have potential application for stress sensor.

Enhancing stem cell therapy efficacy with functional lignin modified cerium-iron nanozyme through magnetic resonance imaging tracking and apoptosis protection in inflammatory environment

Stem cell transplantation provides a promising approach for addressing inflammation and functional disorders. Nonetheless, the viability of these transplanted cells diminishes significantly within pathological environments, limiting their therapeutic potential. Moreover, the non-invasive tracking of these cells in vivo remains a considerable challenge, hampering the assessment of their therapeutic efficacy. Transition-metal oxide nanocrystals, known for their unique “enzyme-like” catalytic property and imaging capability, provide a new avenue for clinical application. In this study, the lignin as a biocompatible macromolecule was modified with poly (ethylene glycol) through chain-transfer polymerization, and then it was utilized to incorporate superparamagnetic iron oxide and cerium oxide nanocrystals creating a functional nanozyme. The iron oxide nanocrystals self-assembled into the hydrophobic core of nano system, while the in-situ mineralization of cerium oxide particles was carried out with the assistance of peripheral phenolic hydroxyl groups. The product, cerium‑iron core-shell nanozyme, enabled effective stem cells labeling through endocytosis and exhibited catalase and superoxide dismutase activities within the cells. As a result, it could scavenge highly destructive hydroxyl radicals and peroxyl radicals, shielding stem cells from apoptosis in inflammatory environment and maintaining their differentiation ability. Additionally, when these functionalized stem cells were administered to mice with acute inflammation, not only did they alleviate disease symptoms, but they also allowed for the visualization using T2-weighted magnetic resonance imaging. This innovative therapeutic approach provides a new strategy for combatting diseases.

Biocompatible polyethersulfone membrane modified by hydrophilic polymer decorated magnetic nanoparticles gilded by facile external magnetic field

AbstractPolymer‐based membranes such as polyethersulfone are widely used for hemodialysis and bio‐related applications; however, this type of membrane still fails to satisfy optimum performance in terms of clearance, safety, and bio‐adaptability. Herein, a polymer brush of polyvinylpyrrolidone is decorated on the surface of magnetic nanoparticles by using reversible addition‐fragmentation chain transfer polymerization (RAFT), and under the guidance of an external magnetic field, the prepared magnetic nanoparticles with the polymer brush system are blended with a polyethersulfone membrane during a liquid‐liquid phase inversion process. The prepared membranes with different loads of the pure magnetic nanoparticle and polyvinylpyrrolidone@magnetic nanoparticle polymer brushes are prepared, compared with the pristine membrane, the modified membrane shows a high flux value at 349 L m−2 h−1 and 99.9% bovine serum albumin protein rejection. This membrane also demonstrated improved hydrophilicity and pore structure compared with the pristine membrane. Concerning the blood biocompatibility analysis, the modified membranes acquire prolonged time for clotting factors such as prothrombin time, activated partial thromboplastin time, and thrombin time while exhibiting less fibrinogen concertation at 0.4 g L−1. Furthermore, for the first time, an innovative method for fouling detection based on magnetic field attenuation due to protein accumulation on the membrane surface is reported; the method in this work could be a positive booster for the safe use of polymeric membranes in hemodialysis and bio‐based applications.

Impact of Zwitterions on the Acidity Constant and Glucose Sensitivity of Block Copolymers with Phenylboronic Acid.

Molecular assemblies that transform in response to pH and saccharide concentration are promising nanomaterials in the field of biomedicine, and polymeric micelles of amphiphilic polymers with phenylboronic acids (PBAs) have been studied. Herein, we report the impact of zwitterions on the acidity constant for the collapse and the glucose sensitivity of a polymeric micelle produced from a diblock copolymer comprising polyacrylamides with PBA and zwitterionic carboxybetaine (PAEBB-b-PCBAAm). The diblock copolymer was synthesized through reversible addition-fragmentation chain-transfer polymerization followed by deprotection. PAEBB-b-PCBAAm produced micellar aggregates in aqueous solutions at a neutral pH, and the polymeric micelles collapsed at a pH of 11.0 because the PBA transformed into a hydroxyboronate anion. The pKa decreased in the presence of glucose owing to boronate ester formation. The PCBAAm chain significantly increased the pH at which the molecular assemblies dissociated. This is probably because the pKa of boronic acid increased through the dipolar interaction of zwitterions, and/or the zwitterionic polymer corona is valid for screening of PBA ionization and electrostatic repulsion of boronate anions. This study on the modulation of pKa through the zwitterionic interaction can facilitate the molecular design of pH- and saccharide-responsive biomaterials.

UCST-Type Thermoresponsive Sol-Gel Transition Triblock Copolymer Containing Zwitterionic Polymer Blocks.

Thermoresponsive sol-gel transition polymers are of significant interest because of their fascinating biomedical applications, including as drug reservoirs for drug delivery systems and scaffolds for tissue engineering. Although extensive research has been conducted on lower critical solution temperature (LCST)-type sol-gel transition polymers, there have been few reports on upper critical solution temperature (UCST)-type sol-gel transition polymers. In this study, we designed an ABA-type triblock copolymer composed of a poly(ethylene glycol) (PEG) block and zwitterionic polymer blocks that exhibit UCST-type thermoresponsive phase transitions. A sulfobetaine (SB) monomer with both ammonium and sulfonate (-SO3) groups in its side chain or a sulfabetaine (SaB) monomer with both ammonium and sulfate (-OSO3) groups in its side chain was polymerized from both ends of the PEG block via reversible addition-fragmentation chain-transfer (RAFT) polymerization to obtain PSB-PEG-PSB and PSaB-PEG-PSaB triblock copolymers, respectively. Although an aqueous solution containing the PSB-PEG-PSB triblock copolymer showed an increase in viscosity upon cooling, it did not undergo a sol-to-gel transition. In contrast, a sol-to-gel transition was observed when a phosphate-buffered saline containing PSaB-PEG-PSaB was cooled from 80 °C to 25 °C. The PSaB blocks with -OSO3 groups exhibited a stronger dipole-dipole interaction than conventional SB with -SO3 groups, leading to intermolecular association and the formation of a gel network composed of PSaB assemblies bridged with PEG. The fascinating UCST-type thermoresponsive sol-gel transition properties of the PSaB-PEG-PSaB triblock copolymer suggest that it can provide a useful platform for designing smart biomaterials, such as drug delivery reservoirs and cell culture scaffolds.

Surface Modification of Cellulose Nanocrystal Films via RAFT Polymerization for Adsorption of PFAS

Cellulose nanocrystals (CNCs) are bio-based materials able to be functionalized following different approaches, which expands their range of applications. One such approach is surface-initiated polymerization, which involves the attachment of an initiator to the CNC’s surface to initiate the growth of the polymer. This work reports the modification of CNCs using the described approach. First, a CNC-based film was prepared, on which an initiator (RAFT agent) was grafted, and then (trimethylaminoethyl methacrylate, a positively charged monomer, was polymerized using reversible addition–fragmentation chain-transfer (RAFT) polymerization. The CNC film was successfully modified and fully characterized. Different degrees of polymerization were targeted to emphasize the effect of the positively charged polymer and their chain length on the adsorption efficiency. The results showed that by increasing the chain length of the grafted polymer, up to 80% of both pollutants could be removed, with a faster adsorption of PFOS as compared to PFOA.

Access to Stereoblock Polyesters via Irreversible Chain-Transfer Ring-Opening Polymerization (ICT-ROP).

Precise control over polymer microstructure can enable the molecular tunability of material properties and represents a significant challenge in polymer chemistry. Stereoblock copolymers are some of the simplest stereosequenced polymers, yet the synthesis of stereoblock polyesters from prochiral or racemic monomers outside of "simple" isotactic stereoblocks remains limited. Herein, we report the development of irreversible chain-transfer ring-opening polymerization (ICT-ROP), which overcomes the fundamental limitations of single catalyst approaches by using transmetalation (e.g., alkoxide-chloride exchange) between two catalysts with distinct stereoselectivities as a means to embed temporally controlled multicatalysis in ROP. Our combined small-molecule model and catalytic polymerization studies lay out a clear molecular basis for ICT-ROP and are exploited to access the first examples of atactic-syndiotactic stereoblock (at-sb-st) polyesters, at-sb-st polyhydroxyalkanoates (PHAs). We achieve high levels of control over molecular weight, tacticity, monomer composition, and block structures in a temporally controlled manner and demonstrate that stereosequence control leads to polymer tensile properties that are independent of thermal properties.