Nanocrystallization-locked Network of Poly(styrene-b-isobutylene-b-styrene)-g-Polytetrahydrofuran Block Graft Copolymer

Abstract

Poly(styrene-b-isobutylene-b-styrene) triblock copolymer (SIBS), a kind of thermoplastic elastomer with biocompatibility and biostability containing fully saturated soft segments, could be synthesized via living cationic copolymerization. A novel poly[(styrene-co-methylstyrene)-b-isobutylene-b-(styrene-co-methylstyrene)]-g-polytetrahydrofuran (M-SIBS-g-PTHF) block graft copolymer was prepared to increase the polarity and service temperature of SIBS by grafting polar PTHF segments onto SIBS. A series of the above block graft copolymers with average grafting numbers from 2 to 6 and molecular weights of PTHF branches ranging from 200 g·mol−1 to 4200 g·mol−1 were successfully synthesized via living cationic ring-opening polymerization of tetrahydrofuran (THF) coinitiated by AgClO4. The introduction of PTHF branches led to an obvious microphase separation due to thermodynamic incompatibility among the three kinds of segments of polyisobutylene (PIB), polystyrene (PS) and PTHF. Moreover, the microphase separation promotes the rearrangement of PTHF branches to form the nanocrystallization-locked physically cross-linked network after storage at room temperature for 2 months, leading to insolubility of the copolymers even in good solvents. The melting temperature and enthalpy of PTHF nanocrystallization locked in hard domains of M-SIBS-g5-PTHF-1.1k block graft copolymer increased remarkably up to 153 °C and 117.0 J·g−1 by 23 °C and 11.6 J·g−1 respectively after storage for long time. Storage modulus (G′) is higher than loss modulus (G″) of M-SIBS-g-PTHF block graft copolymer at temperatures ranging from 100 °C to 180 °C, which is much higher than those of the SIBS triblock copolymer. To the best of our knowledge, this is the first example of high performance M-SIBS-g-PTHF block graft copolymers containing segments of PIB, PS and PTHF with nanocrystallization-locked architecture.