Double isomerization polymerization of optically active cyclic pseudoureas

Five optically active cyclic pseudoureas 2, i.e., (R)-4-ethyl-2-(1-pyrrolidinyl)-2-oxazoline (2a), (R)-4-ethyl-2-morpholino-2-oxazoline (2b), (R)-4-ethyl-2-(2-isoindolinyl)-2-oxazoline (2c), (S)-4-isopropyl-2-(1-pyrrolidinyl)-2-oxazoline (2d), and (S)-4-benzyl-2-(1-pyrrolidinyl)-2-oxazoline (2e), were prepared and their cationic ring-opening polymerization was examined. The polymerization of these monomers with alkyl halides yielded poly[(1,3-diazolidin-2-one-1,3-diyl)oligomethylene]s (main-chain-type polyureas, 3) via the double isomerization polymerization pathway, while that with methyl trifluoromethanesulfonate produced polymers consisting of (N-carbamoylimino)ethylene (pendant-type unit) and (1,3-diazolidin-2-one-1,3-diyl)oligomethylene units due to concurrence of simple ring-opening polymerization of the 2-oxazoline moiety of 2 with double isomerization polymerization.