HYDROGEN-BONDING AND SEQUENCE DISTRIBUTION IN POLY(VINYL ACETATE-CO-VINYL ALCOHOL) COPOLYMERS

The correlation between hydrogen-bonding self-association and sequence distribution in different poly(vinyl acetate-co-vinyl alcohol) copoly mers (ACA) of different degrees of hydrolysis and sequence distributio ns has been studied by infrared and NMR spectroscopy. For ACA copolyme rs, quasi-random distributions are obtained by acid alcoholysis, block ier distributions by saponification, and intermediate distributions by a combined method, as shown by C-13 NMR. FTIR spectroscopy has pointe d out that hydrogen-bonding distribution in ACA copolymers strongly de pends on sequence distribution. For block copolymers, hydroxyl-hydroxy l self-association is preferred, However, in random copolymers, a stro ng competition between hydroxyl-hydroxyl and hydroxyl-carbonyl associa tion is observed. Hydroxyl-carbonyl association seems to occur between adjacent repeat units, leading to cyclic structures with a high therm al stability.