Synthesis of polymers in aqueous solutions. Selective addition reaction of poly(2-isopropenyl-2-oxazoline) with thiols and carboxylic acids in aqueous solutions

Abstract

Convenient addition reactions of 2-methyl-2-oxazoline (1a) and poly(2-isopropenyl-2-oxazoline) (5) with benzenethiol (2a) in the aqueous solution were examined. The reaction of 1a with 2a, which is a model reaction for polymer synthesis, in mixed solvents of N-methyl-2-pyrrolidone (NMP) and water at 60°C for 1 h gave only an adduct N-(2-phenylthioethyl)acetamide (3a) in 72-77% yields. However, adduct 3a and a hydrolysis product N-(2-hydroxyethyl)-acetamide (4) were obtained in 67 and 23% yields, respectively, when the reaction of 1a with equivalent 2a was carried out in water alone at 60°C for 3 h. The addition reactions of pendant oxazoline groups in polymer 5 with thiols such as 2a, 5-thioacetic acid (2c), S-thiobenzoic acid (2d) proceeded quantitatively to give the corresponding polymers (6a, 6c, and 6d) without hydrolysis of the pendant oxazoline groups in the mixed solvents of NMP with water. It was also found that the addition reactions of the pendant oxazoline groups in polymer 5 with 2a proceeded with high conversion and selectively without hydrolysis of the oxazoline groups even when water was used as the reaction medium.