RAFT/MADIX emulsion copolymerization of vinyl acetate and N-vinylcaprolactam: towards waterborne physically crosslinked thermoresponsive particles

Abstract : Well-defined poly(N-vinylcaprolactam-co-vinyl acetate) thermoresponsive particles phys. crosslinked by means of hydrophobic interactions were synthesized by polymn.-induced self-assembly. It was highlighted that a xanthate-terminated poly(ethylene glycol) (PEG-X) efficiently acted as both a stabilizer and a macromol. chain transfer agent for the RAFT/MADIX batch emulsion copolymn. of N-vinylcaprolactam (VCL) and vinyl acetate (VAc), enabling the direct synthesis in aq. dispersed media of PEG-b-P(VAc-co-VCL) block copolymers. It was emphasized that a fraction of 47 mol% of hydrophobic VAc in the second block of the copolymer was suitable for maintaining the integrity of the self-assembled PEG-b-P(VAc-co-VCL) block copolymer particles at low temp. while exhibiting a temp.-induced phase transition. The well-defined phys. crosslinked particles interestingly behaved as thermoresponsive colloids analogous to chem. crosslinked microgels. The PEG-b-P(VAc0.47-co-VCL0.53) particles were able to undergo a reversible swollen-to-collapse transition with increasing temp. in the absence of hysteresis. The PEG-b-P(VAc0.17-co-VCL0.83) block copolymer with a lower fraction of VAc in the copolymer (17 mol%) behaved oppositely as very small objects were present in the aq. phase at low temp. (T \textless 20 °C) and self-assembled into large aggregates by increasing the temp. Finally, the statistical copolymers based on VAc and VCL were successfully hydrolyzed into promising thermoresponsive biocompatible statistical copolymers based on vinyl alc. and N-vinylcaprolactam co-monomer units.