Radical Cyclocopolymerization of a Transformable Divinyl Monomer with a Monovinyl Monomer and Postpolymerization Modification for the Synthesis of AAB-Type Alternating Copolymers Composed of NIPAM and Vinyl Ether

In this work, we successfully synthesized AAB sequence-controlled copolymers of acrylamide (A) and vinyl ether (VE, B) via radical cyclocopolymerization of a diacrylate monomer carrying CF3-disubstututed 2-(hydroxymethyl)phenol as the spacer (1) with an excess of VE and subsequent postpolymerization modification with aminolysis. The rational spacer design introducing two CF3–substituents allowed an efficient cyclopropagation of the divinyl monomer, alternating copolymerization with VE, and quantitative transformation. The copolymerization with 2-methoxyethyl vinyl ether (MOVE) and an aminolysis reaction with isopropylamine gave the NIPAM–NIPAM–MOVE alternating copolymer, and the aqueous solution was transparent at ambient temperature but turned cloudy upon heating. The thermal response behaviors as well as the AAB periodic sequence were evaluated through comparison with AB alternating/statistical copolymers and an N-isopropylacrylamide (NIPAM) homopolymer by temperature-variable transmittance, 1H nuclear magnetic resonance (NMR) (in D2O) measurements, and 13C/1H–13C heteronuclear single quantum coherence (HSQC) NMR spectra.