Synthesis and characterization of thermoresponsive graft copolymers of NIPAAm and 2-alkyl-2-oxazolines by the "grafting from" method

New thermoresponsive graft copolymers were synthesized by the cationic ring-opening polymerization of 2-methyl-2-oxazoline (MeOxa) or 2-ethyl-2-oxazoline (EtOxa), initiated by the random copolymers of chloromethylstyrene (CMS) and N-isopropylacrylamide (NIPAAm) using the "grafting from" method with a yield of 66-94%. The polymers were characterized by NMR, GPC, and DSC, and the conformational transition (lower critical solution temperature, LCST) of macroinitiators and graft copolymers was determined by the turbidity and DSC measurements. The transition temperature of the graft copolymers could be fine-tuned through the composition of the macroinitiator and the graft copolymer. An increasing quantity of the hydrophobic comonomer chloromethylstyrene in the macroinitiator lowered its LCST, while in the graft copolymer an increasing content of the hydrophilic segment of poly(2-methyl-2-oxazoline) or poly(2-ethyl-2-oxazoline) raised the transition temperature. For graft copolymers with a high content of long poly(2-alkyl-2-oxazoline) grafts, stabilized aggregates with a thermoresponsive core can be formed at the LCST instead of precipitation of the material.