Solvent-free, photoinduced block copolymer synthesis from polymerizable eutectics by simultaneous PET-RAFT and ring-opening polymerization in air

Abstract

We report the preparation of poly(N-isopropylacrylamide)-block-poly(ε-caprolactone) (pNIPAM-b-pCL) block copolymers via the simultaneous RAFT polymerization and anionic ring-opening polymerization (ROP) of NIPAM and CL respectively, in the absence of traditional solvents. This was achieved through the formation of a deep eutectic solvent system based on mixtures of NIPAM and CL in various mole ratios, which resulted in a viscous liquid at room temperature. 1D and 2D NMR spectroscopy supported the strong association between NIPAM and CL within the eutectic structure and low-self diffusion coefficients of the monomers within the medium. Through the use of a modified RAFT agent with a terminal hydroxyl group on the R group to facilitate ROP, block copolymers were synthesized via simultaneous photoinduced-electron/energy transfer RAFT (PET-RAFT) and ROP in air using a ruthenium photocatalyst and tin(II) 2-ethylhexanoate as initiator for the respective polymerizations. Low dispersity copolymers were prepared that exhibited living behaviour; the block copolymers displayed thermoresponsive self-assembly behaviour in water due to the presence of the NIPAM block. The use of the polymerizable eutectic gave much higher reaction rates in comparison to the equivalent reactions conducted in typical organic solvents, highlighting the benefit of this synthetic approach.