Synthesis of high-vinyl isoprene and styrene triblock copolymers via anionic polymerization with difunctional t-BuLi initiator

Abstract Triblock copolymers poly(styrene)-block-poly(isoprene)-block-poly(styrene) (PS-b-PI-b-PS, SIS) and poly(isoprene)-block-poly(styrene)-block-poly(isoprene) (PI-b-PS-b-PI, ISI) with different vinyl structure contents were successfully synthesized by anionic polymerization using a difunctional t-BuLi initiator. The difunctional t-BuLi initiator was prepared from tert-butyllithium (t-BuLi) and 1,3-diisopropenylbenzene, and characterized by 1H NMR, 13C NMR, DEPT135, 7Li NMR, and GC-MS analysis. According to the results of 1H NMR, 13C NMR, and 2D HSQC analysis, the contents of 1,2- and 3,4-addition (vinyl group) structures for PI in SIS and ISI were in the range of 3.7%–94.6%, and depended on the reaction temperature and amount of tetrahydrofuran (THF) added. The Mn and PDI of SIS and ISI obtained by GPC were in the ranges of 13,400–281,000 Da and 1.09–1.24, respectively. The presence of two glass transition temperatures (Tg) on the DSC curve indicated microphase separation of the PI and PS domains. The low Tg was attributed to the PI domain, which was correlated with the vinyl group content in the block copolymer. For vinyl group contents of 6.9% and 94.6% in the SIS triblock copolymer, and 6.6% and 94.2% in the ISI triblock copolymer, the corresponding Tg values of the PI block were −64 °C and 12 °C, and −62 °C and 17 °C, respectively.