Thermoresponsive Alternating Copolymers with Tunable UCST Behavior in Aqueous Medium

Abstract

Achieving polymers with upper critical solution temperature (UCST) behavior in aqueous medium under physiological conditions remains a significant challenge, yet it is critically important for designing systems relevant to biomedical applications. Herein, we report the emergence of pH-responsive UCST behavior in water of an alternating copolymer (ACPx) synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization, using a maleimide-appended amine-functionalized monomer (M1) and styrene sulfonate (M2). Temperature-dependent UV-vis spectroscopy was used to understand the dependence of concentration, molecular weight, pH, and salt on cloud point temperature (TCP) of ACPx, while dynamic light scattering (DLS) and transmission electron spectroscopy (TEM) were used to observe the morphological changes with variation of temperature. To verify the role of electrostatic interaction, another styrene-maleimide-based alternating control polymer (CACP) was also prepared, which exhibited UCST behavior only at acidic pH. This study demonstrates that constructing alternating polymers with precise monomer placement enables control over UCST behavior, offering a strategic approach for the development of advanced stimuli-responsive materials.