Investigation of the structure and properties of polyisobutylene-based telechelic ionomers of narrow molecular weight distribution. I.

Abstract

The solid state morphology of recently developed sulfonated polyisobutylene (PIB) telechelic ionomers with narrow molecular weight distribution (MWD) (M¯w/M¯n ≈ 1.15) was investigated. A small angle X-ray scattering (SAXS) peak often associated with the aggregation of the ionic species in the bulk, as well as a secondary peak, have been observed in the narrow distribution sulfonated PIB telechelic ionomers for the first time. Ionomers of difunctional and tri-arm architecture at several number average molecular weights (M¯n) with one of several counterions were investigated and the preparation method was also considered in terms of observed SAXS behavior. Compression-molded films made from these narrow MWD telechelics were examined in detail using SAXS. Primary and secondary peaks were observed in the slit-smeared SAXS profiles up to an M¯n of 27 kg/mol. The ratio of the interdomain spacings derived from these peaks (ca. 2 : 1) suggests cylindrical or lamellar ordering in the morphology in both difunctional and tri-arm ionomers. Pinhole SAXS images showed no azimuthal dependence in the scattering pattern and thus, this ordering is on a local scale. It was found that the counterion has an inconsistent effect on the smeared interdomain spacing associated with the SAXS peak. The smeared interdomain spacings were systematic with respect to architecture and M¯n for solution cast Cs+ ionomers. The difunctional telechelics exhibited higher smeared interdomain spacings than tri-arms of comparable M¯n and unlike the compression-molded films, the smeared interdomain spacings of the solution cast Cs+ telechelic ionomers increased systematically with increasing M¯n. Even a broad MWD (M¯n/M¯n ≈ 1.8) tri-arm telechelic ionomer M¯n of 20.6 kg/mol exhibited a diffuse primary peak in SAXS when solution-cast. However, it exhibited no peak when compression-molded. © 1997 John Wiley & Sons, Inc.