Small-angle X-ray scattering studies of zinc stearate-filled sulfonated poly(ethylene-co-propylene-co-ethylidene norbornene) ionomers

The crystallization, melting, and dissolution behavior of zinc stearate (Zn St) in ZnSt-filled sulfonated poly(ethylene-co-propylene-co-ethylidene norb ornene) (SEPDM) ionomers was studied by synchrotron small-angle X-ray scatt ering (SAXS). The melting temperature of ZnSt in the ionomer was considerab ly lower than in the pure state, which was consistent with the existence of very small ZnSt crystalline domains and a specific interaction between the metal sulfonate groups of the SEPDM and the metal carboxylate groups of Zn St. Temperature-resolved SAXS showed that, on melting, some or all of the Z nSt rapidly dissolved into the ionomer. Ionic aggregates in the neat ionome r persisted up to 300 degrees C. Microphase separation was also observed at elevated temperatures for the ZnSt-filled ionomers, but the composition of the microdomains was believed to be quite different than that of the micro domains in the neat SEPDM. The time and temperature dependence of the ZnSt crystallization in the filled ionomers was characterized by time-resolved S AXS experiments following a temperature quench from the melt. (C) 1999 John Wiley & Sons, Inc.