The ring-opening polymerizations of 2-phenyl-5,6-dihydro-4H-1,3-oxazine (PhOZI) with methyl tosylate (MeOTs) and butyl iodide (BuI) as initiators were performed in refluxing butyronitrile. Reaction kinetics under microwave irradiation was compared with conventional oil bath heating. The polymerization rates, under microwave irradiation, showed an acceleration by a factor of 1.8 (independently from the used initiator). The investigation of the thermal properties of the obtained poly(N-benzoyl-trimethyleneimine) showed the influence of molecular weight and end-groups on the glass transition temperature.