RING-OPENING ISOMERIZATION POLYMERIZATION OF CYCLIC IMINOCARBONATES

Five- (1) and six-membered cyclic iminocarbonates (2) having primary or secondary alkoxy substituents were newly prepared and the cationic ring-opening polymerization of them was examined. The polymerization of 2-ethoxy-2-oxazoline (1a) with methyl trifluoromethanesulfonate proceeded smoothly at 20-degrees-C and yielded poly[[N-(ethoxycarbonyl)imino]ethylene] (4a) in a high yield, although the degree of polymerization was around 10 due to the chain transfer involving the 2-ethoxy substituent of the propagating species. The chain transfer was suppressed in the polymerization of 1 having a bulky alkoxy group, e.g., 2-(neopentyloxy)-2-oxazoline (1e). The reaction of 1a with a catalytic amount of alkyl halide, on the other hand, yielded no polymeric product but an isomerized product, 3-ethyl-2-oxazolidone, instead. The mechanism for polymerization, chain transfer, and isomerization were discussed and the ring-opening polymerizabilities of 2-isopropoxy-2-oxazoline (1b) and 2-isopropoxy-5,6-dihydro-4H-1,3-oxazine (2b) were compared with those of their 2-methyl homologues on the basis of kinetic results.