Homopolymer-block-Alternating Copolymers Composed of Acrylamide Units: Design of Transformable Divinyl Monomers and Sequence-Specific Thermoresponsive Properties

In this work, we synthesized an acrylamide-based terpolymer that is a block copolymer composed of an AB alternating copolymer and a C homopolymer. The key to the unprecedented achievement is rational design of an acrylate–acrylamide divinyl monomer carrying CF3-substituted salicylic acid ester bonds (AAm-CF 3 ) to realize the efficient and selective cyclopolymerization as well as the quantitative transformation of the resultant cyclorepeating units. The selectivity in the cyclopolymerization and the pendant transformation ability were evaluated through reactivity ratios of the corresponding model monomers and quantitative aminolysis reactions of the model compound. The cyclopolymerization via the photoinduced electron transfer-reversible addition–fragmentation chain transfer (PET-RAFT) process with a macrochain-transfer agent and subsequent aminolysis reaction afforded the homopolymer-block-alternating copolymer. The sequence-controlled terpolymer exhibited a very unique thermal response behavior in water that was strikingly different from the corresponding sequence-uncontrolled terpolymers, such as homopolymer-block-statistical copolymers and all statistical terpolymers, despite the fact that the structure cannot be distinguished by 1H NMR.