In-Situ Direct Mechanistic Transformation from RAFT to Living Cationic Polymerization for (Meth)acrylate−Vinyl Ether Block Copolymers

Cationic RAFT polymerization using ppm concentrations of organic acid

A metal-free, cationic, reversible addition-fragmentation chain-transfer (RAFT) polymerization was proposed and realized. A series of thiocarbonylthio compounds were used in the presence of a small amount of triflic acid for isobutyl vinyl ether to give polymers with controlled molecular weight of up to 1×10(5) and narrow molecular-weight distributions (Mw /Mn <1.1). This "living" or controlled cationic polymerization is applicable to various electron-rich monomers including vinyl ethers, p-methoxystyrene, and even p-hydroxystyrene that possesses an unprotected phenol group. A transformation from cationic to radical RAFT polymerization enables the synthesis of block copolymers between cationically and radically polymerizable monomers, such as vinyl ether and vinyl acetate or methyl acrylate.

Precision synthesis of bio-based acrylic thermoplastic elastomer by RAFT polymerization of itaconic acid derivatives

Bio-based polymer materials from renewable resources have recently become a growing research focus. Herein, a novel thermoplastic elastomer is developed via controlled/living radical polymerization of plant-derived itaconic acid derivatives, which are some of the most abundant renewable acrylic monomers obtained via the fermentation of starch. The reversible addition-fragmentation chain-transfer (RAFT) polymerizations of itaconic acid imides, such as N-phenylitaconimide and N-(p-tolyl)itaconimide, and itaconic acid esters, such as di-n-butyl itaconate and bis(2-ethylhexyl) itaconate, are examined using a series of RAFT agents to afford well-defined polymers. The number-average molecular weights of these polymers increase with the monomer conversion while retaining relatively narrow molecular weight distributions. Based on the successful controlled/living polymerization, sequential block copolymerization is subsequently investigated using mono- and di-functional RAFT agents to produce block copolymers with soft poly(itaconate) and hard poly(itaconimide) segments. The properties of the obtained triblock copolymer are evaluated as bio-based acrylic thermoplastic elastomers.

Direct Mechanistic Transformations from Isotactic or Syndiotactic Living Anionic Polymerizations of Methyl Methacrylate into Metal-Catalyzed Living Radical Polymerizations

The mechanistic transformations from living anionic polymerizations into living radical polymerizations were examined after halogenating the growing terminal during the stereospecific living anionic polymerization of methyl methacrylate (MMA), directly forming a macroinitiator with a covalent carbon-halogen terminal for subsequent transition metal-catalyzed living radical polymerizations. The quantitative halogenation of the living isotactic or syndiotactic PMMA anion, prepared using tBuMgBr in toluene or diphenylhexyllithium (DPHLi) in THF, respectively, was achieved using CCl₃Br or CCl₄ as a halogen source in the presence of strong Lewis bases, such as 1,8-diazabicyclo[5.4.0]undec-7-ene, to generate stereoregular PMMA with a C-X (X = Br or Cl) bond. The halogenated terminal was then transformed into the radical species through a one-electron redox reaction of the ruthenium catalysts to allow the living radical polymerization of styrene or MMA, resulting in block copolymers that consisted of stereoregular PMMA and polystyrene segments or stereoblock PMMAs.