New polyisobutylene-based model ionomers

Strain induced crystallization has been observed at 25°C in low molecular weight three-arm star polyisobutylene ionomers at elongations exceeding about 550%. The sulfonated form of the polymer was neutralized with calcium hydroxide. The number average molecular weight of the polymer was only 9,000 with a dispersity ratio of about 1.7. This molecular weight is at the edge of the critical molecular weight for entanglements. Strain induced crystallization has been reported in the literature for very high molecular weight linear polyisobutylene. However, no such effects have been observed for linear, low molecular weight polyisobutylene and it has been stated it could not be induced. The cause for this strain induced crystallization in our materials is due to the presence of three ionic terminal groups per molecule which results in sufficient coulombic forces for maintenance of molecular orientation with strain without significant relaxation.