Papers by Keyword: RAFT Polymerization

Abstract: The influence of various tacticity regulators on the reversible addition-fragmentation (RAFT) polymerization of 2,2,3,3-tetrafluoropropyl methacrylate in the presence of 2-cyano-2-propyldodecyltritiocarbonate as an chain transfer agent was investigated. Among Lewis acids considered, the polymerization of TFPMA in dioxane with ZnBr₂ turned out to be the most effective from the point of view of tacticity; the polymer with the highest isotacticity is formed. The addition of hexafluoroisopropanol leads to an increase in the heterotacticity and a decrease in the isotacticity of the polymer chain.

Abstract: The copolymerization of 1,1,1,3,3,3-hexafluoroisopropyl acrylate (HFIPA) and glycidyl methacrylate via reversible addition-fragmentation chain transfer (RAFT) process was investigated. 2-cyano-2-propyl dodecyl trithiocarbonate (CPDT) was used as chain transfer agent. It is turned out that CPDT and polymeric chain transfer agent obtained based on HFIPA and CPDT provide a good control over molar mass characteristic of copolymers (Đ = 1.05). Reactivity ratios were found to be r₁(GMA) = 1.57 and r₂(HFIPA) = 0.05 by Fineman–Ross model.

Abstract: The oral administration of pharmaceuticals is typically preferred over other methods due to its non-intrusiveness and convenience of administration. However, the varying chemical environments of the gastro-intestinal tract pose a challenge in ensuring the stability and inertness of a drug compound until it reaches its target. Polymers that are responsive to pH changes have potential as smart materials for the controlled oral administration of pharmaceuticals. In this study, linear and hyperbranched copolymers of methacrylic acid (MAA) and poly (ethylene glycol) methyl ether methacrylate (PEGMEMA) were synthesized by RAFT polymerization. High molecular weight polymers were produced with PDI values close to 1.0. These smart materials underwent phase changes at pH 5.15-5.6. This property enabled the amphiphilicity of the copolymers to be switched on or off. By doing so in in vitro drug release studies with ibuprofen as the model hydrophobic drug, the copolymers were able to inhibit drug release in simulated stomach conditions to up to 13% while enhancing drug release in simulated intestinal conditions to up to 75% within 6 hours. These indicate that copolymers based on MAA and PEGMEMA have potential as smart materials for drug delivery applications.

Abstract: Diverse nanostructural materials including spheres, nanorods, vesicles, and large compound vesicles have been created via formation of amphiphilic ABA triblock copolymers, self-assembling and morphology transition in the reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization. The polymerization of styrene (St) was performed in a selective solvent, methanol, using S,S′-bis(α,α′-dimethyl-α′′-acetic acid)-trithiocarbonate terminated poly(N,N-dimethylacrylamide) (PDMAa-TC) as macro chain transfer agent and stabilizer, and 1H NMR, and TEM were used to monitor the polymerization.

Abstract: pH-Responsive polymers have attracted much attention for biotechnology applications as carriers or matrix to facilitate intracellular or extracellular therapeutic drug delivery and release. In this paper, we report the development of new pH-responsive and hyperbranched copolymers with potential for such applications. These pH-responsive hyperbranched copolymers were synthesized via one pot reversible addition-fragmentation chain transfer (RAFT) copolymerization of propylacrylic acid (PAA) and a branching co-monomer poly(ethylene glycol diacrylate) (PEGDA) (Mn=258 Da) at the monomer feed molar ratios [PAA]0/[PEGDA]0 = 99/1, 90/10 and 80/20. The resultant poly(PAA-PEGDA) copolymers were characterized by Proton Nuclear Magnetic Resonance (1H NMR) and Gel Permeation Chromatography (GPC) to obtain the molecular weight, copolymer composition and degree of acrylate functionality. The hydrodynamic dimensions of these copolymers at pH range between 5.0 and 7.4 were studied using Dynamic Light Scattering technique (DLS). Moreover, these hyperbranched copolymers demonstrated composition- and size-dependent membrane disruptive properties by red blood cell hemolysis assay. Poly(PAA-PEGDA) with the copolymer composition [PAA]/[PEGDA]= 68/32, obtained from the copolymerization at the monomer feed molar ratio [PAA]0/[PEGDA]0 = 99/1, demonstrated significant membrane disruptive activity.

Abstract: Well-controlled polystyrene-b-poly (n-butyl acrylate)-b-polystyrene (PSt-b-PnBA-b-PSt) triblock copolymers were prepared by RAFT (reversible addition-fragmentation chain transfer) emulsion polymerization process. The mechanical properties of the triblock copolymers were investigated in comparison to the P(nBA-co-St) statistical copolymers. When the PSt content is 20%, the ultimate tensile strength of triblock copolymer is nearly six times the strength of statistical copolymer, while their modulus are all around 3.0×10³ Pa. The triblock copolymer films feel smooth and non-tacky as the PSt content is higher than 20%. It indicates that PSt-b-PnBA-b-PSt triblock copolymers can be used as binders in pigment dyeing, providing the dyed fabrics with soft non-tacky handle and good fastness properties.

Abstract: PMMA-b-PDMAEMA/polysulfone composite membranes for CO₂ separation was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization techniques. The chemical composition and structure of the polymers were characterized by Fourier transform infrared (FT-IR) spectroscopy, nuclear magnetic resonance (NMR), and molecular weight and its distribution were measured by Gel permeation chromatography (GPC). CO₂ permeation performance of the PMMA-b-PDMAEMA/ polysulfone composite membranes was test. The results showed that the resulted composited membrane posses good permeation performance for CO₂.

Abstract: A series of linear poly(2-hydroxyethyl methacrylate) (PHEMA) with defined molecular weights (MW) and narrow molecular distributions were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization using cumyl dithiobenzoate (CDB) as a chain transfer agent. Murine fibroblasts (3T3) were exposed to eluates from various PHEMA samples, washed or unwashed, and with or without dithioester end groups. After 72 hrs in cell culture, no cytotoxic response was elicited by the polymer samples devoid of dithioester end groups, and which also underwent a thorough washing regime. Specimens throughout the entire MW range were internalized by a macrophage (cell line Raw 264), suggesting that such polymers can be used as models for studying the biodegradation of PHEMA.

Abstract: A nonapeptide, which is sensitive to enzymatic digestion by collagenase, was modified by the covalent attachment of an acrylamido group at the terminal positions. The functionalized peptide was used as a crosslinking agent during polymerization of 2-hydroxyethyl methacrylate (HEMA). Reversible addition-fragmentation chain transfer (RAFT) method was used to obtain a polymer (PHEMA) with an average theoretical molecular weight of 4000 Da, containing enzymatically labile peptide crosslinks. The functionalized peptide was analyzed in detail by 1H and 13C nuclear magnetic resonance (NMR) spectrometry. The polymerization reaction was monitored by near infrared spectrometry, while the resulting polymer was analyzed by size exclusion chromatography and solid NMR spectrometry. The peptide-crosslinked PHEMA was subjected to an in-vitro degradation assay in the presence of collagenase. At the highest concentration of enzyme used in the study, a weight loss of 35% was recorded after 60 days of incubation in the collagenolytic medium. This suggests that crosslinking with enzymatically degradable peptides is a valid method for inducing biodegradability in polymers that otherwise are not degradable.

Abstract: Tri-block copolymer with pH- and thermo-responsive consisting of poly(t-butylacrylate) and poly(vinylcaprolactam), (PtBA/PVCL) were prepared by RAFT polymerization and characterized by gel permeation chromatography (GPC) and 1H NMR. PtBA and PVCL were used as macro chain-transfer agents (MCTA) to synthesize PtBA-b-PVCL-b-PtBA and/or PVCL-b-PtBA-b-PVCL, which after partial hydrolysis led to amphiphilic tri-block copolymers P(tBA-co-AA)-b-PVCL-b-P(tBA-co-AA) and/or PVCL-b-P(tBA-co-AA)-b-PVCL.