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

摘要

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 H-1 NMR, C-13 NMR, DEPT135, Li-7 NMR, and GC MS analysis. According to the results of H-1 NMR, C-13 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 M-n 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 (T-g) on the DSC curve indicated microphase separation of the PI and PS domains. The low T-g 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 T-g values of the PI block were -64 degrees C and 12 degrees C, and -62 degrees C and 17 degrees C, respectively.