New Thermoplastic Elastomers with Enhanced Elongation at Break, Elastic Recovery, and Upper Use Temperature

There has been intense interest in block copolymers as thermoplastic elastomers (TPEs) since the 1960s. To date, the single largest application for block copolymers has been as TPEs. TPEs combine the ease of processing and recyclability of thermoplastics with the mechanical properties of crosslinked elastomers. The most important TPEs commercially are ABA triblock copolymers, made anionically and having glassy A blocks of polystyrene (PS) and rubbery B blocks composed of polydienes (PI or PBD).

Work in our laboratory over the past 25+ years has focused on how changing the macromolecular topology from a linear triblock to a branched multigraft copolymer structure can be used to tune and enhance mechanical properties. This change keeps the chemical composition the same so all mechanical property improvements observed must be attributed to beneficial tuning of macromolecular architecture. Therefore, any property improvements should be possible to achieve in all classes of TPEs. We have systematically demonstrated that employing a multigraft copolymer architecture, as compared tom an ABA triblock copolymer architecture, will lead to very large enhancements in elongation at break with greatly enhanced elastic recovery. The modulus of the copolymer may also be tuned widely by adjusting architecture.

In addition, we have explored benzofulvene as a promising “new monomer” for synthesis of TPEs capable of being used at higher temperatures. This monomer undergoes living anionic polymerization and polybenzofulvene (PBF) has a Tg around 150 °C that can be tuned by adjusting the microstructure of the PBF. For the development of TPEs having higher upper use temperature, well-defined homopolymers and block copolymers containing PBF blocks were synthesized by sequential living anionic polymerization. Promising elastomeric materials were obtained.