Developing high temperature thermoplastic elastomers based on benzofulvene by living anionic polymerization in hydrocarbon solvent at room temperature

Thermoplastic elastomers (TPEs) are of great importance both academically and technologically. Currently TPEs are predominating styrenic-diene copolymers. However, these styrenic TPEs have serious limitations in applications, especially at higher temperature, because of their low upper service temperature (UST). Here we present a new class of TPEs with higher UST based on benzofulvene, an anionicly polymerizable monomer in hydrocarbon solvent at room temperature. Polybenzofulvene-b-polyisoprene-b-polybenzofulvene (FIF) triblock copolymers of four different compositions were synthesized through a difunctional lithium-based initiator (DLI) in benzene. These synthesized triblock copolymers retained their storage modulus up to 150°C before dropping off proved by dynamic mechanical analysis (DMA). Tensile test revealed FIF with 14 vol% of polybenzofulvene has maximum 1400% strain with a tensile strength of 17 MPa. Small angle X-ray scattering showed microphase separation between polybenzofulvene and polyisoprene but without long range order. Partial and complete hydrogenation of FIF triblock were performed and resulting polymers showed different mechanical properties but improved thermal stability. Study of 1,2- and 1,4- microstructure of polybenzofulvene homopolymers was carried out in benzene with different polar additives such as sec-Butoxide (sec-BuOLi), 1,2-dipiperidinoethane (DiPIP), 1,2-dimethoxyethane (DME). The glass transition temperature analyzed from differential scanning calorimetry (DSC), respectively, were 153°C, 161°C and 191°C at molecular weight of 20kg/mol. Thus, synthesizing high temperature thermoplastic elastomers with potential of tunable service temperature by incorporating polybenzofulvene as a new building blocks is possible.