Stereoregularity of poly(vinyl ether)s with a narrow molecular weight distribution obtained by the living cationic polymerization

Abstract

The stereoregularity of poly(isobutyl vinyl ether) with a narrow molecular weight distribution obtained by the living cationic polymerization in toluene at +40∼−78°C was studied. As an initiating system, 1-(isobutoxy)ethyl acetate/EtAlCl2 was used in the presence 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 13C NMR spectroscopy and compared with that of the non-living polymer obtained in the absence of added bases. The diad fraction and the temperature coefficient of ln(Pm/Pr) for the living polymerization were equal to those for the non-living polymerization. The ΔHm≠−ΔHr≠ was determined to be −900 cal mol−1, indicating that meso-rich poly(isobutyl vinyl ether) was synthesized favorably at low temperature polymerization. A counteranion and an added base in the living cationic polymerization of IBVE did not affect obviously the stereostructure 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°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 polymerization in the presence of ethyl acetate. The ln(Pm/Pr) vs. 1/T curve had a maximum at about +20°C, and it decreased with decreasing the polymerization temperature and became constant at the lower temperature below 0°C. The facts and the profile about polymerization rates suggested a stabilization of the propagating carbocation by the side ester group of the terminal unit through an intramolecular interaction. © 1993, The Society of Polymer Science, Japan. All rights reserved.