Kinetics and mechanism of cationic polymerization of 5-methyl-2-oxazoline. Concurrent propagation through ionic and covalent species with methyl iodide initiator

Abstract

Kinetic analysis of the cationic polymerization of 5-methyl-2-oxazoline (5-MeOZO) was performed with methyl tosylate(MeOTs) and methyl iodide(MeI) initiators by using 1H NMR spectroscopy. With MeOTs the polymerization of 5-MeOZO proceeded through oxazolinium tosylate species 3 and 4 and the rate constant of propagation (kp) was determined. With MeI, on the other hand, the propagating ends are present in equilibrium between alkyl iodide (covalent) species 7, 9 and 11 and oxazolinium(ionic) species 6, 8 and 10. Two model reactions enabled to determine the equilibrium constant (K) of 6/7 and to evaluate the reactivity of covalent species 9 (reflected by kp(c)) and of ionic species 8 (reflected by kp(i)). Both species 8 and 9 propagate concurrently and contribute to the whole propagation at comparative extents.