Thermoresponsive properties of poly(acrylamide-co-acrylonitrile)-based diblock copolymers synthesized (by PISA) in water

Abstract

In this present work, we report the synthesis of UCST-thermoresponsive diblock copolymers using reversible addition fragmentation chain transfer (RAFT) polymerization in aqueous media. A water-soluble poly(N,N-dimethylacrylamide) macromolecular chain transfer agent (PDMAc macroRAFT) is used to promote and control the copolymerization of acrylamide and acrylonitrile in water and obtain PDMAc-b-P(AAm-co-AN) diblock copolymers. The f_AN,0 and the length of the thermosensitive block (DP_n) are systematically varied, in order to study their influence on the thermoresponsiveness of the block copolymers. A good blocking efficiency is generally evidenced by size exclusion chromatography. Remarkably, amphiphilic copolymer nanoparticles are formed in situ for the highest f_AN,0. This is indeed the first time that such particles are produced by a polymerization-induced self-assembly (PISA) process. The morphology of the in situ formed nanoparticles and their behavior with temperature are studied by means of dynamic light scattering (DLS), (cryogenic) transmission electron microscopy ((cryo-)TEM) and turbidimetry. Spherical and worm-like nanoparticles are formed which exhibit unexpected properties, such as an unprecedented heating-induced worm-to-sphere morphological transition in water.