IONIC AND CHAIN INTERDIFFUSION AND INTERFACIAL STRENGTH DEVELOPMENT IN IONOMERS OF POLY(ETHYLENE-CO-METHACRYLIC ACID)

Diffusion coefficients of sodium and zinc ions have been measured in b ilayers of commercial, partially neutralized poly(ethylene-co-methacry lic acid). The diffusion behavior shows a break at the melting tempera ture of the resin, suggesting that chain backbone motion is intimately related to ionic transport. The ionic diffusion coefficients are orde rs of magnitude greater than those of the chain backbone, which sugges ts that metal ion pairs are transported along the contour of the polym er network via exchange with protons of neighboring acid groups. Inter facial strength development in welded films of ionomers is primarily d etermined by the melting behavior of the bulk resin. Ionic diffusion r ates do not correlate with the strength development behavior. This obs ervation, along with melting and chain center of mass diffusion inform ation, suggests that strength development is dependent on chain interd iffusion like that of many other thermoplastics.