Thermoplastic interpenetrating polymer networks of a triblock copolymer elastomer and an ionomeric plastic. I. Rheology and morphology

Abstract

The thermoplastic interpenetrating polymer networks (IPNs) are combinations of two physically crosslinked polymers. Thermoplastic IPNs were prepared by combining polymer I, an SEBS triblock elastomer with polymer II, an ionomer prepared from a random copolymer of styrene, methacrylic acid, and isoprene (90/10/1 by volume). Neutralization of the acid groups to form the ionomer was carried out on a Brabender Plasticorder. Two subclasses of the thermoplastic IPNs were identified. Chemically blended systems, prepared by a sequential polymerization method, were compared with compositionally equivalent mechanically blended systems prepared by melt blending the separately synthesized polymers. The chemically blended thermoplastic IPNs (CBT IPNs) exhibited lower melt viscosities than compositionally equivalent mechanically blended thermoplastic IPNs (MBT IPNs). Moreover, the melt viscosities of many of the CBT IPNs were even lower than that of either homopolymer component, leading to an explanation in terms of an unusually low value of the rubbery modulus front factor. Although both types of thermoplastic IPNs underwent a phase inversion during neutralization of polymer II, the phase inversions were often incomplete. Morphological studies revealed that more equal dual phase continuity existed in the MBT IPNs than in the CBT IPNs after ionomer formation.