Polymerization and copolymerization of 5-oxazolones

A series of 5-oxazolones were investigated in an attempt to establish a chain-growth ring-opening polymerization of the heterocycle. The two types of 5-oxazolones studied were 2,4-disubstituted-5-oxazolones and 2-unsubstituted-5-oxazolones. Product analyses enabled discrimination between the two types of 5-oxazolones regarding their relative polymerizabilities.

2,4-Disubstituted-5-oxazolones were found to selectively dimerize tinder base catalysis. Cationic initiation of 2,4-disubstituted-5-oxazolones yielded neither dimeric nor polymeric materials. However, cationic initiation of solutions of 2-unsubstituted-5-oxazolones yielded poly (N-formyl-α-amino acids) of moderate molecular weight. This represents the first example of chain-growth polymerization of 5-oxazolones and the first one-step synthesis of this type of polymer.

The nucleophilic character of the 5-oxazolone ring was evidenced by its cationic polymerization and was utilized in a novel alternating copolymerization with two electrophilic monomers, acrylamide and 2-hydroxyethyl acrylate. Thus, four new 1:1 alternating copolymers were synthesized in moderate yields. Product analyses of these copolymers are presented and their mechanisms are discussed.