Living Cationic Polymerization of tert-Butyl Vinyl Ether by Organoaluminum Halides in the Presence of Added Bases

Abstract

Living cationic polymerization of tert-butyl vinyl ether (TBVE) was achieved by the 1-(isobutoxy)ethyl acetate (1)/Et1.5AlCl1.5 initiating system in the presence of THF in hexane at −20°C. The polymers had a very narrow molecular weight distribution (M̅w/M̅n≤1.1), and M̅n increased directly proportional to the monomer conversion. On the other hand, under conditions suitable for the living polymerization of isobutyl vinyl ether (e.g., 1/EtAlCl2 initiating system, methyl acetate as added base, temperatures higher than 0°C), non-living polymers of TBVE with a broader molecular weight distribution were obtained. For the living polymerization of such a highly reactive monomer as TBVE, combinations of added bases having stronger basicity, weaker Lewis acid activators, and low temperature turned out to be indispensable. Using this system, the high molecular weight poly(TBVE) with a narrow molecular weight distribution was also obtained (M̅n=1.1×105, M̅w/M̅n=1.11). The tert-butyl groups of the poly(TBVE) were quantitatively deprotected (99.9%) by bubbling HBr gas, to yield poly(vinyl alcohol). To elucidate the polymerization characteristics of TBVE, neo-pentyl vinyl ether and three isomers of butyl vinyl ethers (n-butyl vinyl ether, isobutyl vinyl ether, and sec-butyl vinyl ether) were polymerized, and polymerization behavior is discussed on the basis of the sterical structures of side alkyl groups.