Thermoresponsive behavior of graft copolymers based on poly(N,N-dimethylacrylamide-co-diacetoneacrylamide) side chains

A thermoresponsive graft copolymer was synthesized through free radical copolymerization and a "graft onto" method in aqueous solution. The primary structure of the graft copolymer is constituted of a partially hydrolyzed polyacrylamide (HPAM) backbone and thermosensitive side chains [amino-terminated poly(N,N-dimethylacrylamide-co-diacetone acrylamide) or P(DMA-co-DAAM)] with molecular weight around 10(5) g/mol. The H-1-NMR spectra at various temperatures showed the temperature of thermoassociation (T-ass) in the copolymer. At the same time, the pyrene fluorescence measurements demonstrated the formation of hydrophobic microdomains of P(DMA-co-DAAM) above T-ass. The thermothickening behavior of the graft copolymers was studied by viscosity measurements, and the results suggested that in semidilute solutions, the T-ass and the magnitude of thermothickening could be regulated by varying the hydrolysis degree of the backbone, the composition of side chains, and the addition of NaCl. The oscillatory shear experiments demonstrated that the copolymer can present a remarkable elasticity increase as the temerature increased to T-ass. These thermoassociating copolymers with temperature-tunable properties can have potential applications as smart materials in enhanced oil recovery. (c) 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 135, 47051.