Sequence-Defined Phase Behavior of Poly(N-Isopropylacrylamide-co-Acrylamide) in Water

The precise arrangement of different chemical moieties in a polymer determines its thermophysical properties. How the sequence of moieties impacts the properties of a polymer is an outstanding problem in polymer science. Herein, we address this problem for the thermoresponsive property of poly(N-isopropylacrylamide-co-acrylamide) in water using all-atom molecular dynamics (MD) simulations. Eight distinct copolymers, each with a different arrangement of NIPAM(N-isopropylacrylamide) and AM (acrylamide) monomers, are considered. The lower critical solution temperature (LCST) shows a strong correlation with the mean block length of the periodic sequences of the copolymer. We further identify copolymer sequences that exhibit both the LCST and upper critical solution temperature (UCST). Moreover, there are sequences that do not show any LCST or UCST for the temperature range explored in this study. This wide variability in thermorepsonsive property is found to be closely linked to the the extent of hydrongen bond formation in the system, which appears to have a significant correlation with the monomer sequence of the copolymer. These findings offer new directions in the design of structurally diverse thermoresponsive copolymers.