Reversible Addition-fragmentation Polymerization Research Articles

RAFT Polymerization of 2,2,3,3-Tetrafluoropropyl Methacrylate in the Presence of Lewis Acids

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.

Synthesis of PMMA-b-PEG-b- PMMA by controlled Polymerization Using Macro-RAFT Agents

In this work controlled radical polymerization (CRP) of methyl methacrylate was carried out in thepresence of the Poly(ethylene glycol)(PEG) xanthate reversible addition fragmentation (RAFT) chain transferagent designated as (CTA1) and (CTA2). Firstly, PEGs having different molecular weights (400 and 600 g/mol)were reacted KOH and CS2 and the terminated 4-chloro benzoyl chloride to obtain PEG-xathates. RAFT agentpossessing PEG chain was used in the RAFT polymerization of MMA to yield PMMA-b-PEG-b-PMMA tri-blockcopolymers which can be used in various potential applications. With the gravimetric follow of the reaction, thecontrol mechanism works well and the molecular weight has grown linearly. The structures of the synthesizedmacro RAFT agents and polymers were characterized by 1H-NMR, 13C-NMR and FT-IR spectroscopic methods.

Supramolecular poly(N-acryloylmorpholine)-b-poly(d,l-lactide) pseudo-block copolymer via host-guest interaction for drug delivery

In the present study, a pseudo-block copolymer was prepared from β-cyclodextrin terminated poly(N-acryloylmorpholine) (β-CD-PNAM) and adamantine-terminated linear poly(D,L-lactide) (AD-PDLLA), through host-guest interaction between β-CD and AD groups. Initially, the hydrophilic polymer PNAM was synthesized using reversible addition fragmentation polymerization, which was further linked to N3-β-CD through click reaction. In parallel, an AD terminated hydrophobic polymer, AD-PDLLA was synthesized using ring opening polymerization. The synthesized polymers were characterized by means of 1H NMR, gel permeation chromatography and fourier transform infrared. Subsequently, the formation of a pseudo-block copolymer via inclusion complexation between the β-CD core and AD-moiety was confirmed by 2D-NOESY NMR and self-aggregation of the pseudo-block copolymer was investigated by fluorescence spectroscopy. In addition, doxorubicin (DOX) a hydrophobic drug was loaded into the supramolecular micelles and the release kinetics of DOX from the micelles was studied. The result revealed that DOX release was accelerated as the pH reduced from 7.4 to 6.4.

Hyperbranched Glycopolymers of 2-(α-d-Mannopyranose) Ethyl Methacrylate and N,N'-Methylenebisacrylamide: Synthesis, Characterization and Multivalent Recognitions with Concanavalin A.

A series of novel hyperbranched poly[2-(α-d-mannopyranosyloxy) ethyl methacrylate-co-N,N’-methylenebisacrylamide] (HPManEMA-co-MBA) are synthesized via a reversible addition fragmentation polymerization (RAFT). The dosage ratios of linear and branch units are tuned to obtain different degree of branching (DB) in hyperbranched glycopolymers. The DB values are calculated according to the content of nitrogen, which are facilely determined by elemental analysis. The lectin-binding properties of HPManEMA-co-MBA to concanavalin A (ConA) are examined using a turbidimetric assay. The influence of defined DB value and molecular weight of HPManEMA-co-MBA on the clustering rate is studied. Notably, HPManEMA-co-MBAs display a low cytotoxicity in the MTT assay, thus are potential candidates for biomedical applications.

Synthesis of Poly(lactic acid)-block-poly(N,N-dimethylaminoethyl methacrylate) Copolymers with Controllable Block Structures via Reversible Addition Fragmentation Polymerization from Aminolyzed Poly(lactic acid)

Poly(lactic acid)-block-poly(N,N-dimethylaminoethyl methacrylate) (PLA-PDMAEMA) copolymers were synthesized from aminolyzed PLA via reversible addition fragmentation (RAFT) polymerization. PLA undergoes aminolytic degradation with ethylenediamine (EDA). The kinetics of the aminolysis reaction of PLA at different temperatures and EDA concentrations was investigated in detail. The molar masses of products rapidly decreased in the initial stage at low aminolytic degree. Meanwhile, reactive –NH2 and –OH groups were introduced to the end of shorter PLA chains and used as sites to further immobilize the RAFT agent. PLA-PDMAEMA block copolymers were synthesized. A pseudo-first-order reaction kinetics was observed for the RAFT polymerization of PDMAEMA at a low conversion. By controlling the aminolysis reaction of PLA and RAFT polymerization degree of DMAEMA, the length distributions of the PLA and PDMAEMA blocks can be controlled. This method can be extended to more systems to obtain block copolymers with controllable block structure.

Modulation of cell adhesion and detachment on thermo-responsive polymeric surfaces through the observation of surface dynamics

Various thermo-responsive polymeric surfaces were evaluated in terms of cell adhesion/detachment and surface analysis. Three kinds of thermo-responsive poly(N-isopropylacrylamide) (PIPAAm) surfaces were prepared by an electron beam irradiation (PIPAAm-EB), a reversible addition fragmentation polymerization (PIPAAm-RAFT), and a redox polymerization (PIPAAm-Redox). Although cell adhesion and detachment on surfaces of PIPAAm-EB and PIPAAm-RAFT were able to be modulated by altering their surface characters with changing the amounts of polymers, the adhesion and detachment were hardly controlled on PIPAAm-Redox surfaces, even though the amounts of polymers on the surface were able to be modulated. Atomic force microscopy (AFM) probed the interactions between AFM tip and the polymeric surface for further investigating a different conformation of polymeric surface. The modification of AFM tip surface coated with octadecyltrichlorosilane was found to change the interaction between the thermo-responsive surface and the tip. Adhesion force analysis clearly showed changes in the hydrophilic/hydrophobic characters of three kinds of thermo-responsive surfaces immediately after a change in temperature. From the kinetics study of AFM, PIPAAm-EB and PIPAAm-RAFT surfaces became hydrophilic less than 30min after temperature decrease, but PIPAAm-Redox surfaces required 120min to become hydrophilic after temperature reduction. These results indicated that a faster conformational change triggered cell detachment and a slow conformation change hardly affected cell detachment. Therefore, polymeric conformation on solid substrate was an important factor for modulating cell adhesion and detachment.

Electro‐optical properties of polymer dispersed liquid crystal prepared by successively controlled living radical polymerization

AbstractPolymer dispersed liquid crystal (PDLC) films were obtained by successive controlled living radical polymerizations: starting polystyrene (M1) was obtained by reversible addition‐fragmentation polymerization (RAFT), M1 was converted to P‐chloromethylated polystyrene (M2) which was grafted with polystyrene branches by atom transfer radical polymerization (ATRP) to yield RAFT‐initiating graft polymer containing trithiocarbonate moieties in the backbone (M3, RAFT‐active grafted polystyrene), and then PDLC films were prepared by photo‐induced RAFT copolymerization of methyl acrylate with M3 in the presence of a nematic liquid crystal. The electro‐optical properties of the films were investigated for the purpose to apply them to optical devices. Experimental results showed that preferable properties could be acquired by controlling the amount of M3 and the liquid crystal E7 in the polymer matrix of PDLC films. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers

A readily modified polyethersulfone with amino-substituted groups: Its amphiphilic copolymer synthesis and membrane application

An amino-substituted polyethersulfone (PES) was synthesized by the polycondensation of a functional monomer bis(3-amino-4-hydroxyphenyl) sulfone with bis(4-fluorophenyl) sulfone. The amine groups incorporated into PES were employed as anchors to immobilize the chain transfer agents of reversible addition-fragmentation polymerization (RAFT). The resultant macro chain transfer agent was used to initiate the polymerization of the hydrophilic monomers N-isopropyl acrylamino (NIPAAm) and N, N-dimethylamino-2-ethyl methacrylate (DMAEMA), respectively. The gel permeation chromatography (GPC) results confirmed the successful synthesis of the amphiphilic copolymers PES- g-PNIPAAm and PES- g-PDMAEMA, and these two copolymers were perhaps the few examples of amphiphilic copolymer synthesized via a radical polymerization from PES main chains. The amino-substituted PES seemed a versatile precursor that showed a potential of functionalization via various strategies including click chemistry, atom transfer radical polymerization and RAFT polymerization. The synthesized amphiphilic copolymers were finally used as additives to improve the hydrophilicity and the filtration performances of PES membranes.