Poly(styrene- b-isobutylene- b-styrene) block copolymer ionomers (BCPI), and BCPI/silicate nanocomposites. 1. Organic counterion: BCPI sol–gel reaction template

Abstract

Silicate structures were inserted along the cylindrical polystyrene (PS) domains in an ionomer form of elastomeric poly(styrene- b-isobutylene- b-styrene) tri-block copolymers, via in situ sol–gel reactions. Environmental scanning electron microscopy/energy dispersive X-ray spectroscopy studies indicated that silicate structures do in fact grow within the interior of ca. 0.8 mm thick films rather than forming undesirable silica precipitates on the surface. The combination of a domain-selective swelling solvent (DMAc) and the attachment of large organic counterions (benzyltrimethylammonium) along the styrene blocks facilitated the preferential migration of hydrolyzed Si(OEt) 4 monomers to these ionic domains where the sol–gel reactions are apparently seeded. Differential scanning calorimetry and dynamic mechanical studies indicated that T g for the polyisobutylene (PIB) phase is essentially unaffected, but the PS phase T g shifts to higher values with ionomer formation, and to even higher values with subsequent silicate phase insertion. These two methods provide indirect evidence that the silicate component is mainly incorporated in the PS rather than PIB domains. Combined with the results of earlier atomic force microscopy studies that demonstrated that the basic morphology of the unmodified block copolymer is unchanged despite the insertion of a silicate phase, the data presented here reinforce the concept of a robust sol–gel reaction template. Also, the rubbery plateau storage modulus was elevated as a result of ionomer formation and more so after the ionomer was imparted with a silicate phase, which illustrates mechanical reinforcement.