Initiation of RAFT Polymerization: Electrochemically Initiated RAFT Polymerization in Emulsion (Emulsion eRAFT), and Direct PhotoRAFT Polymerization of Liquid Crystalline Monomers

Abstract

We report on two important advances in radical polymerization with reversible addition–fragmentation chain transfer (RAFT polymerization). (1) Electrochemically initiated emulsion RAFT (eRAFT) polymerization provides rapid polymerization of styrene at ambient temperature. The electrolytes and mediators required for eRAFT are located in the aqueous continuous phase separate from the low-molar-mass-dispersity macroRAFT agent mediator and product in the dispersed phase. Use of a poly(N,N-dimethylacrylamide)-block-poly(butyl acrylate) amphiphilic macroRAFT agent composition means that no added surfactant is required for colloidal stability. (2) Direct photoinitiated (visible light) RAFT polymerization provides an effective route to high-purity, low-molar-mass-dispersity, side chain liquid-crystalline polymers (specifically, poly(4-biphenyl acrylate)) at high monomer conversion. Photoinitiation gives a product free from low-molar-mass initiator-derived by-products and with minimal termination. The process is compared with thermal dialkyldiazene initiation in various solvents. Numerical simulation was found to be an important tool in discriminating between the processes and in selecting optimal polymerization conditions.

Multiblock Copolymer Synthesis via Reversible Addition–Fragmentation Chain Transfer Emulsion Polymerization: Effects of Chain Mobility within Particles on Control over Molecular Weight Distribution

“…Multiblock copolymer synthesis via RDRP has become a prominent research topic since it was realized in 2011 for Cu(0)-mediated radical polymerization, and shortly thereafter for reversible addition–fragmentation chain transfer (RAFT) polymerization, that multiple consecutive polymer blocks can be grown for high conversion without intermittent purification under carefully considered conditions that guarantee high livingness (chain-end fidelity). In recent years, RDRP has been exploited for the synthesis of multiblock copolymers of increasing intricacy. ,,,− RAFT polymerization, in particular, has proven itself highly viable for multiblock copolymer synthesis because of its good monomer compatibility, robustness to various polymerization techniques and conditions, superior performance in dispersed systems, and the large assemblage of accumulated interest and literature availablity. − The synthesis of multiblock copolymers is characterized by the controlled polymerization of constituent monomers, with final material properties tailored via the block composition, length and sequence; such methodologies, however, lend themselves to certain complications. The issues with reduced chain-end fidelity, monomer compatibility, and long reaction times, while maintaining acceptable molecular weight distributions (MWDs), are obstacles that become even more pertinent as the block length and the number of involved monomer species increase.…”

The difference between photo-iniferter and conventional RAFT polymerization: high livingness enables the straightforward synthesis of multiblock copolymers

“…One defining trait of PI–RAFT is the reversible deactivation and the resulting increased chain end fidelity of the method when compared to conventional RAFT polymerization. While it was demonstrated that irreversible termination is still present, 37 in a typical PI–RAFT process reversible deactivation is deemed to be the main fate of growing radical. Indeed, it is even hypothesized that this mechanism is able to control a polymerization.…”

Random and Diblock Thermoresponsive Oligo(ethylene glycol)-Based Copolymers Synthesized via Photo-Induced RAFT Polymerization

“…Most studies are focused on the typical monomers involved in radical polymerization: methyl methacrylate, methyl acrylate, dimethylacrylamide, styrene, etc. [ 12 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. Far less research has been conducted on the preparation of bottlebrush polymers through visible light-mediated polymerization.…”