Synthesis of a Thermally Self-Curable Poly(styrene-<i>b</i>-isobutylene-<i>b</i>-styrene) Triblock Copolymers Using a Highly Chemoselective Divinyl Cross-Linker

A divinyl cross-linker, 1-((1,2,2-trifluorovinyl)oxy)-4-vinylbenzene (TFVS), was synthesized and incorporated into a triblock copolymer of styrene and isobutylene (SIBS). The block copolymer was prepared through living cationic polymerization initiated with bifunctional cumyl ether in the presence of TiCl4, a strategy developed by Kennedy and co-workers. Sequential feeding of monomers was applied in which isobutylene was polymerized in the first step, followed by the copolymerization of styrene and TFVS. The two vinyl groups in TFVS exhibited remarkable selectivity during cationic polymerization: the styrenic moiety readily copolymerized with styrene, while the trifluorovinyl moiety remained unreacted. The resulting triblock copolymer, poly(styrene-co-TFVS)-b-polyisobutylene-b-poly(styrene-co-TFVS), hereafter referred to as SFIBSF, was subject to a cross-linking reaction during molding at high temperatures (180–200 °C) through [2π + 2π] thermal cycloaddition between trifluorovinyl ether moieties in polystyrene segments. The molded sample, Fx-SFIBSF, demonstrated superior mechanical properties due to the synergistic interplay of physical and chemical cross-linking. It achieved a tensile strength of up to 30 MPa, an elastic recovery of 73.9%, and excellent creep resistance, with a maximum reduction of creep strain of 80%. These findings pave the way for the development of a new generation of polyisobutylene-based elastomers with enhanced performance and expanded application potential.