Chain Transfer Research Articles

Deciphering the function of Zn(Et)2 in tailoring comonomer insertion sequence during coordinative chain transfer ethylene/propylene copolymerization

Deciphering the function of Zn(Et)2 in tailoring comonomer insertion sequence during coordinative chain transfer ethylene/propylene copolymerization

Synthesis and properties of block polycarboxylate dispersant containing benzene ring side groups by catalytic chain transfer polymerization (CCTP)

Synthesis and properties of block polycarboxylate dispersant containing benzene ring side groups by catalytic chain transfer polymerization (CCTP)

Synthesis of Telechelic Isotactic Polypropylenes for Circular Polypropylene-like Materials via Chain Transfer Polymerization.

While synthesizing circular polymers with telechelic polyolefin building blocks recently emerged as a promising strategy for addressing conventional polyethylenes' sustainability challenges, the lack of telechelic iPP (tPP) with sufficient difunctional purity for polycondensation has been limiting the development of circular polypropylenes with iPP-like structures and properties. Here we described a combined approach of coordinative chain transfer polymerization and transition-metal-catalyzed quenching reaction with various acyl chlorides, affording tPPs with a high difunctional ratio (up to ∼99%) and broad end functional group scope. The steric effect of polymeryl-Zn species and the role of Pd catalyst were revealed by DFT. This method also solved the low difunctional ratio challenge for telechelic polyethylenes. Ester-linked iPPs with iPP-like structure and thermomechanical properties and PE/iPP multiblock copolymers were synthesized by the resulting tPPs.

An Anticoagulant Coating Based on a Block Phosphocholine Copolymer for Potential Applications in Blood Contact Devices

AbstractAs the core component of ventricular assist devices, blood pumps have been widely used in clinical treatment. However, the thrombus caused by the contact of the inner surface of the blood pumps with blood still remain a serious risk. The zwitterionic coating has the ability to form a hydration layer to inhibit the protein and blood cell adhesion, which makes it a potential strategy to solve the coagulation on the device. Herein, a phosphocholine zwitterionic coating is presented and formed by a block copolymer poly(2‐methylacryloxyethyl phosphatecholine‐b‐glycidyl methacrylate (PMPC‐b‐GMA). Poly(MPC) and poly(GMA) are intended to provide, respectively, resistance to thrombus formation and adhesion to the material surface. The copolymers are synthesized through reversible addition‐fragmentation chain transfer polymerization to achieve an accurate molecular design. After dip‐coated on the materials, the phosphocholine coating exhibits protein and platelet resistance ability, anticoagulant ability, and in vitro biocompatibility. Furthermore, the in vivo biocompatibility is confirmed through the implantation of the coated polycarbonate substrate in rats. This study provides a promising pathway for regulating the interaction between biomaterials and proteins, platelets, and bioactive molecules, and is expected to guide the further development of anticoagulant coatings to ensure the safety of blood contact devices in clinical treatment.

Synthesis, characterization and cytotoxicity analyzes of novel AB-Type Amphiphilic Block Copolymers

AB-type novel amphiphilic poly(L-lactide)-block-(N-isopropylacrylamide) (PLLA-b-PNIPAM) and poly(L-lactide)-block-(N-vinyl-pyrrolidone) (PLLA-b-PNVP), diblock copolymers were synthesized through the combined use of ring-opening polymerization (ROP) and controlled/living radical polymerization (CRP) techniques. (PLLA-b-PNIPAM) block copolymer was prepared via combination of ROP and atom transfer radical polymerization (ATRP) using the novel PLLA-based ATRP macroinitiator. (PLLA-b-PNVP) block copolymer was synthesized via combination of ROP and reversible addition-fragmentation chain transfer (RAFT) polymerization using the PLLA-based RAFT macro chain transfer agent (CTA). For this purpose, at first 2,4-difluorobenzyl alcohol (1) was used to initiate the ROP of (L-LA) using tin(II) 2-ethylhexanoate Sn(Oct)2 as a catalyst at 120 ℃ for synthesis of PLLA-OH (2). Secondly, bromoester end-functionalized PLLA-based ATRP macroinitiator (3) was synthesized by esterification of hydroxyl end group of (2). The first block copolymer, (PLLA-b-PNIPAM) (5), was synthesized by ATRP of NIPAM using (3) in presence of copper(I) chloride/tris[2-(dimethylamino)ethyl]amine (CuCl/Me6TREN) as catalyst system in DMF/water at 25 °C. For the synthesis step of second block copolymer, at first PLLA macro chain transfer agent (CTA) (4) was then synthesized via substitution reaction of (3) with potassium ethyl xanthogenate (KEX) and finally PLLA-b-PNVP (6) diblock copolymer was prepared via RAFT polymerization of NVP using (4). The molecular structures of novel polymers (2-6) were elucidated by spectroscopic (FTIR and 1H NMR) methods. In the application phase of this study, the effectiveness of copolymers was examined on cervical cancer cells. Cytotoxicity effects were evaluated in vitro on HeLa cell lines.

Stability and Controlled Polymerization of Trithiocarbonate Chain Transfer Agents Under Harsh Conditions

Stability and Controlled Polymerization of Trithiocarbonate Chain Transfer Agents Under Harsh Conditions

Preparation of Ethylene-1-Hexene Copolymers with Bimodal Molecular Weight Distribution and Optimal Branching Distribution on a Highly Active Supported Vanadium-Magnesium Catalyst

Using a new modification of a highly active vanadium-magnesium catalyst (VMC), data were obtained on the effect of hydrogen and hexene-1 content on the catalyst activity and the molecular structure of the resulting polymers. It was found that the formation of polyethylene (PE) with a wide bimodal molecular weight distribution (MWD) on VMC is associated with the presence of two groups of active centers in these catalysts, differing in their reactivity in the polymer chain transfer reaction with hydrogen. It was also found that the presence of hexene-1 during copolymerization leads to an additional broadening of the MWD of the copolymer due to a predominant decrease in the molecular weight of the copolymer in the low-molecular region. At the same time, the active centers of the VMC, producing a high-molecular polymer, practically do not participate in the chain transfer reaction with hexene-1. At the same time, these centers are more reactive in the reaction of insertion of hexene-1, which leads to an increased content of butyl branches in the high-molecular fraction of the copolymers. The kinetic features of highly active VMCs found indicate their promise for the production of pipe and film grades of PE using a one-reactor scheme instead of a two-reactor scheme used to produce bimodal PE on traditional titanium-magnesium catalysts.

A Baicalin-Based Functional Polymer in Dynamic Reversible Networks Alleviates Osteoarthritis by Cellular Interactions.

Osteoarthritis (OA) is increasingly recognized as a whole-organ disease predominantly affecting the elderly, characterized by typical alterations in subchondral bone and cartilage, along with recurrent synovial inflammation. Despite the availability of various therapeutics and medications, a complete resolution of OA remains elusive. In this study, novel functional hydrogels are developed by integrating natural bioactive molecules for OA treatment. Specifically, baicalin (Bai) is combined with 2-hydroxyethyl acrylate (HEA) to form a polymerizable monomer (HEA-Bai) through esterification, which is subjected to reversible addition-fragmentation chain transfer (RAFT) polymerization to produce Bai-based polymer (Pm). These macromolecules are incorporated into Schiff-base hydrogels, which demonstrate excellent mechanical properties and self-healing performance. Notably, the Bai-based formulations are taken up by fibroblast-like synoviocytes (FLSs), where they regulate glycolysis. Mechanistically, inhibition of yes-associated protein 1 (YAP1) by the formulations suppressed the FLSs glycolysis and reduced the secretion of inflammatory factors, including interleukin 1β (IL-1β), IL-6, and IL-8. Furthermore, the functional hydrogel (AG-Pm)-OC, severing as a lubricant and nutrient, prolonged joint retention of Bai, thereby reducing cartilage degradation and synovial inflammation. Meanwhile, (AG-Pm)-OC alleviated joint pain by targeting the YAP1 signaling and inhibiting macrophage recruitment and polarization. Taken together, this flavonoid-based injectable hydrogel exhibits enhanced biocompatibility and efficacy against OA.

Chain transfer to monomer – the main chain-growth termination reaction in radical ring-opening polymerization of ketene acetals

Chain transfer to monomer – the main chain-growth termination reaction in radical ring-opening polymerization of ketene acetals

Graft-to/Graft-From Synthesis of Janus Graft Copolymers for Bottlebrush Polymer Electrolytes.

Janus graft copolymers, which combine the characteristics of block and graft copolymers, have been used in the fields of reaction catalysis, surface modification, and drug delivery, but their applications in lithium batteries have rarely been reported. Herein, Janus graft copolymers with polyethylene glycol (PEG) and polystyrene (PS) side chains are synthesized by combining reversible addition-fragmentation chain transfer (RAFT) polymerization and atom transfer radical polymerization (ATRP) methods and doped with lithium salts to fabricate Janus bottlebrush polymer electrolytes (PEG-J-PS). The PEG side chains of the brush polymers impart good ion-conducting properties to the electrolytes, while the PS side chains improve the mechanical strength and thermal and chemical stability of the electrolytes. Notably, the PEG-J-PS can effectively improve the motility of the polymer chain segments compared to the conventional block copolymer electrolytes (PEG-b-PS). The prepared PEG-J-PS exhibits a considerable ionic conductivity of 2.06 × 10-5 S cm-1 at 30°C and high tensile stress (2.39MPa) and tensile strain (143%) of the PEG45-J-PS20 owing to its Janus graft structure.

Glycosylation profiling of monkeypox virus structural proteins with poly Ser-Arg materials.

Although the glycosylation of viral proteins plays a critical role in the process of viral invasion into host cells, studies on the glycosylation of monkeypox virus (MPXV) structural proteins have not yet been reported. To investigate the importance of MPXV protein glycosylation, poly Ser-Arg (poly SR) materials capable of simultaneously enriching both N-glycopeptides and O-glycopeptides were synthesized by surface-initiated reversible addition-fragmentation chain transfer (SI-RAFT) polymerization. The poly SR materials were evaluated using the digest mixture of standard proteins containing bovine fetuin and bovine serum albumin, and the digest of complex biological samples including bovine sperm tail lysate, mouse sperm tail lysate, mouse brain lysate, and human serum. The poly SR materials demonstrated excellent glycopeptide enrichment performance. Subsequently, poly SR materials were applied to comprehensively analyze the N-glycosylation and O-glycosylation of the MPXV structural proteins A29, A35, B6R, and H3L, revealing that these proteins are highly sialylated. To further elucidate the mechanism of MPXV protein infection, the strong specific binding of A29 to heparan sulfate and chondroitin sulfate was determined using glycan microarrays. These findings provide a foundation for understanding the viral infection mechanism and developing vaccines and antiviral drugs.

Computer modeling of the synthesis of styrene–butadiene rubber: Influence of the feed of a chain transfer agent on the characteristics of the product

Objectives. To develop mathematical approaches and algorithms for analyzing the influence of various methods for feeding a chain transfer agent to a cascade of reactors, taking into account the choice of feed points on the characteristics of the final product of copolymerization using computer modeling.Methods. The processes of synthesis of copolymers were mathematically modeled using a statistical approach (Monte Carlo method). The developed algorithm is based on calculating the probabilities of elementary reactions in the process under study. In the case of continuous production of the copolymer in a cascade of reactors, it must be taken into account that the residence time of each particle of the reaction mixture in the reactor is subject to a probability distribution. The algorithm models the formation of copolymer macromolecules at the particle level, permitting the average molecular characteristics of the copolymer to be calculated and its microstructure to be studied based on modeling results.Results. The dependencies of the intrinsic viscosity on the reactor number and conversion were constructed by means of mathematical modeling. The calculation results showed satisfactory agreement with the experimental data obtained in production. The dependencies of the molecular weight distribution of the copolymer, the weight-average molecular weight, and the microheterogeneity index on the reactor number were constructed for various methods of feed of the chain transfer agent, i.e., to two and/or three points of the reactor cascade. The modeling and calculation results confirmed the influence of the method of adding the chain transfer agent to the cascade reactors on the molecular characteristics of the copolymer.Conclusions. The analysis of the structure of the molecular units of the styrene–butadiene copolymer showed a decrease in the weightaverage molecular weight of the final product and an increase in its stiffness in the case of the three-point feed of the chain transfer agent.

Dielectrically Monitored Flow Synthesis of Functional Vaccine Adjuvant Mixtures via Microwave-Assisted Catalytic Chain Transfer Processing

A novel flow process to produce low-molecular-weight (Mwt) methacrylate oligomer mixtures that have potential as vaccine adjuvants and chain transfer agents (CTAs) is reported. The chemistry and process were designed to significantly reduce the number of stages required to manufacture methyl methacrylate oligomer-in-monomer mixtures with an oligomer Mwt range of dimers to pentamers and >50% conversion. Combining rapid in-flow, in situ catalytic chain transfer polymerization catalyst synthesis and volumetric microwave heating of the reaction medium resulted in catalyst flow synthesis being completed in <4 min, removing the need to pre-synthesize it. The steady-state operation was then successfully maintained with very low levels of external energy, as the process utilized the reaction exotherm. The microwave process outperformed a comparative conventionally heated system by delivering a 20% increase in process throughput with no change in final product quality or conversion. Additionally, combining flow and in situ catalyst processing enabled the use of a more oxidatively unstable catalyst. This allowed for in situ catalyst deactivation post-generation of the oligomers, such that residual catalyst did not need to be removed prior to preparing subsequent vaccine adjuvant or CTA screening formulations. Finally, dielectric property measurements were able to monitor the onset of reaction and steady-state operation.

Bioderived copolymer alternatives to poly(styrene-co-maleic anhydride) via RAFT-mediated copolymerization.

Poly(styrene-co-maleic anhydride) (SMAnh) is a petroleum-based copolymer with desirable properties that afford utility in both industrial and academic fields. The reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization of the bioderived comonomers, indene and itaconic anhydride, was explored using three chain transfer agents with varying activity, and generally well-controlled (Đ < 1.40) polymerizations were observed.

Functional Polyolefins and Composites.

Polyolefins are simple hydrocarbons that require additional chemical modifications or functional additives to give them custom functions. Recent research in the development of functional polyolefins has surpassed the traditional approach of simply improving surface properties by incorporating polar moieties. Creating custom functionalized polyolefins by using specific functional units has attracted increasing attention. This review summarizes advances in preparing custom functionalized polyolefin materials using functional units such as comonomers, chain-transfer agents, post-polymerization modification reagents, and functional fillers. Exploring new functional units and innovative synthetic strategies will further enhance the performance and expand the applications of functional polyolefins.

Evaluation of Controlled Radical Polymerization Using Trithiocarbonate Chain Transfer Agent

Evaluation of Controlled Radical Polymerization Using Trithiocarbonate Chain Transfer Agent

Hydration and Biodistribution of Zwitterionic Dendrimers Conjugating a Sulfobetaine Monomer and Polymers.

Zwitterionic polymers exhibit strong hydration, high biocompatibility, and antifouling properties. Dendrimers are regularly branched polymers, which are used in the drug delivery system (DDS). In this study, we synthesized zwitterionic monomer- and polymer-conjugated dendrimers as a biocompatible nanoparticle to investigate the relation between the hydration property and biodistribution. A sulfobetaine monomer (SBM) was conjugated at the termini of the polyamidoamine (PAMAM) dendrimer. Polysulfobetaines (PSBs) were produced by reversible addition-fragmentation chain transfer polymerization and were also conjugated at the termini. Intermediate water, that is, water molecules loosely bound to the material, can be estimated from the melting peaks at less than 0 °C in differential scanning calorimetry (DSC) measurement. Our DSC results showed that the PSB-conjugated dendrimers (PSM-dens) contained more intermediate water than the SBM-conjugated dendrimer (SBM-den). PSB-dens accumulated in the tumor after intravenous administration, but SBM-den did not. These suggested that the amount of intermediate water, that is, the hydration property, was related to the biodistribution of the zwitterionic dendrimers. This relation is a possible design criterion for drug carriers. PSB-dens accumulated in the tumor even after the second injection, possibly overcoming the accelerated blood clearance observed with poly(ethylene glycol)-modified nanoparticles. Thus, this kind of zwitterionic polymer-conjugated dendrimer is useful for the DDS in cancer treatment.

Rapid 3D printing of unlayered, tough epoxy-alcohol resins with late gel points via dual-color curing technology.

Additive manufacturing technologies and, in particular, vat photopolymerization promise complex structures that can be made in a fast and easy fashion for highly individualized products. While the technology has upheld this promise many times already, some polymers are still out of reach or at least problematic to print reliably. High-performance epoxide-based resins, which are regulated by chain transfer via multifunctional alcohols, are a typical example of resins with late gel points, which require long irradiation times and high light intensities to print. Therefore, we have developed a dual-colour printing approach where rapid radical curing of a soft, wide-meshed polymer network facilitates fast and easy 3D structuring of the subsequently slow curing step-growth formulation at an orthogonal initiation-wavelength regime. Thereby the methacrylate system acts as a scaffold for an uncured epoxide alcohol system during the printing process, which is then cured with UV light post-printing. This way tough alcohol-regulated epoxy-systems become accessible to vat photopolymerization achieving outstanding high-resolution 3D printed parts without significant layering effects. The demonstrated wide-meshed matrix-assisted printing approach has the potential to make a multitude of slowly curing resins accessible to vat photopolymerization techniques, at low irradiation intensities and high curing speeds.

Modular addition strategy-regulated polymerization-induced self-assembly: an in silico experiment.

We propose a modular addition strategy-regulated polymerization-induced self-assembly (PISA) system to effectively control the reaction kinetics and self-assembly morphologies. We validated this strategy by performing in silico experiments on a well-established PISA system. Two categories of modular addition strategies, i.e., the multistep addition strategy and the constant rate addition strategy, were investigated. Results showed that the modular addition operation of macromolecular chain transfer agents (macro-CTAs) effectively regulated the width of the molecular weight distribution for the hydrophobic PSt block, which further led to an assembly of vesicle structures with irregular aspherical cavities. Besides, we found a new transition pathway for the formation of vesicles, which involved generation of small vesicles in the early stage followed by a gradual growth in the intermediate and late stages. In the constant rate addition strategy, with the increase in the addition rate of macro-CTA, we found that the morphology basically tended to change from a micellar structure to a vesicle structure. This study holds potential to inspire future work toward the improvement of experimental techniques in PISA-relevant systems.

Synthesis of multifunctional PEDOT-block copolymers by combining controlled and chemical oxidative polymerization for bioelectronics

This article presents the synthesis of the first EDOT-based RAFT chain transfer agent and a new family of multifunctional PEDOT-block copolymers (PEDOT-b-PMMA, PEDOT-b-PSS and PEDOT-b-PNIPAM) for different bioelectronic applications e.g. OECTs.