Thermoplastic Elastomers with High Service Temperature and Thermal Stability through Hydrogenation of Polybenzofulvene-Based Triblock Copolymers Synthesized by Living Anionic Polymerization

Thermoplastic elastomers (TPEs) have drawn considerable attention in both academic and technological realms over the past century owing to their high elasticity and easy processing. However, conventional TPEs, e.g., polystyrene-b-polyisoprene-b-polystyrene (SIS) or polystyrene-b-polybutadiene-b-polystyrene (SBS), exhibit low upper service temperature (UST) and low thermal degradation temperature (Td), limiting their applications in extreme conditions, as for example, firefighting and aerospace work in high temperature. Herein, we designed polybenzofulvene (PBF)-based triblock copolymer (PBF-b-PI-b-PBF, FIF) TPEs by living anionic polymerization, where PBF as the hard block, dominating the service temperature range, showed an elevated UST due to reduction of torsional degrees of freedom for the polystyrene structure with the introduction of the conjugated cyclopentadiene pentagon. To further check the chemical structure of the hard phase (PBF) on the UST and Td, hydrogenation of the unsaturated bonds in PBF was conducted, that may also improve the chemical resistance. Our results demonstrated that one optimized TPEs (FIF-14, 14 volume percentage of PBF in the triblock copolymer) showed an effective increase of Tg of hard block to 140 °C (from 95 °C of SIS). With the complete hydrogenation, Tg of the hard block in FIF-14 was kept at 130 °C, while the Td increased to 350 °C. Furthermore, this hydrogenated FIF-14 showed robust mechanical properties (Young's modulus of 36.9 MPa and ultimate stress exceeding 16.8 MPa) due to the suitable domain-size microphase separation, showing a great potential service in high temperature.