NOVEL Filler-Interactive Butyl-Type Thermoplastic Elastomers: Potential Replacement of Halobutyl Rubber

The first polyisobutylene (PIB)-based thermoplastic elastomers (TPE) with good mechanical properties (SIBS triblock, M_n = 62,000 g/mol, M_w/M_n = 1.24, 30 wt% polystyrene, 18 MPa ultimate tensile strength at 380 % elongation) were produced using a bifunctional initiator, TiCl₄ coinitiator, a proton trap and an Electron Pair Donor, and sequential addition of styrene after the consumption of IB. SIBS is now produced commercially (Kaneka’s SIBSTAR) and is also used as the coating of the Taxus coronary stent, considered to be the most successful medical device of all times. However, linear triblocks have M_n < 200,000 g/mol, because the high viscosity of the reaction solution prohibits achieving higher molecular weights. Later star-blocks were also produced. Inimers yielded branched polymers and reached M_n up to 1 million g/mol. However, all systems were restricted to rather expensive initiators and TiCl₄ as coinitiator, used in large excess over the initiator. Recently we reported a new two-phase living carbocationic polymerization. Specifically, the copolymerization of IB and Alloocimene, a terpene derived from renewable resources, showed living character up to ~6 minutes or 40 % conversion under the rather inexpensive traditional butyl rubber polymerization conditions (H₂O/AlCl₃ in MeCl at -95 °C) and yielded diblock, triblock and multiblock copolymers exhibiting TPE properties. This is the first example of a diblock exhibiting TPE properties. The new TPEs were reinforced with silica and carbon black fillers. Reinforced diblocks showed as much as 1000% increase in the ultimate tensile strength, while triblocks and multiblocks displayed 50-100 % increase. These new TPEs are promising new biomaterials.