The effect of residual acetate groups on the structure and properties of vinyl alcohol-ethylene copolymers

Vinyl alcohol-ethylene (VAE) copolymers, commercially manufactured by hydro lysis of the corresponding vinyl acetate-ethylene copolymers, can contain s mall amounts of unhydrolyzed vinyl acetate. This article shows the influenc e of these residual groups on the structure of the resulting copolymers, st udied by nuclear magnetic resonance and wide-angle X-ray scattering. Therma l and mechanical properties of these materials were investigated by differe ntial scanning calorimetry, thermogravimetry, drawing behavior, birefringen ce measurements, and dynamic mechanical analysis. The structure of the copo lymers is considerably affected by the volume of the residual acetate group s, bigger than that of the hydroxyl ones, which hinders the crystallization process. In relation to the thermal and mechanical properties, the tempera ture and enthalpy of melting as well as the Young's modulus and yield stres s, decrease as vinyl acetate molar fraction increases. Moreover, the alpha and beta relaxations are shifted to lower temperatures as residual content in the copolymer is raised. (C) 2000 John Wiley & Sons, Inc.