STEREOREGULARITY OF POLY(VINYL ETHER)S WITH A NARROW MOLECULAR-WEIGHTDISTRIBUTION OBTAINED BY THE LIVING CATIONIC POLYMERIZATION

The stereoregularity of poly(isobutyl vinyl ether) with a narrow molec ular weight distribution obtained by the living cationic polymerizatio n in toluene at +40 approximately -78-degrees-C was studied. As an ini tiating system, 1-(isobutoxy)ethyl acetate/EtAlCl2 was used in the pre sence of methyl acetate or methyl pivalate as an added base, which can stabilize the propagating carbocation by the nucleophilic interaction . The stereostructure was determined as a diad fraction by C-13 NMR sp ectroscopy and compared with that of the non-living polymer obtained i n the absence of added bases. The diad fraction and the temperature co efficient of ln(P(m)/P(r)) for the living polymerization were equal to those for the non-living polymerization. The DELTAH(m)not-equal - DEL TAH(r)not-equal was determined to be -900 cal mol-1, indicating that m eso-rich poly(isobutyl vinyl ether) was synthesized favorably at low t emperature polymerization. A counteranion and an added base in the liv ing cationic polymerization of IBVE did not affect obviously the stere ostructure of polymers obtained. The stereoregularity of seven living poly(vinyl ethers) having various side groups was investigated. Benzyl vinyl ether (meso: 89%) and 2-benzoyloxyethyl vinyl ether (meso: 75%) gave meso-rich living polymers in the presence of ethyl acetate as an added base at 0-degrees-C. On the other hand, the stereostructure of living poly(2-benzoyloxyethyl vinyl ether) obtained in the absence of added bases (meso: 58%) was quite different from that for the living p olymerization in the presence of ethyl acetate. The ln(P(m)/P(r)) vs. 1/T curve had a maximum at about +20-degrees-C, and it decreased with decreasing the polymerization temperature and became constant at the l ower temperature below 0-degrees-C. The facts and the profile about po lymerization rates suggested a stabilization of the propagating carboc ation by the side ester group of the terminal unit through an intramol ecular interaction.