Synthesis of butadiene/isoprene–styrene di-block copolymer with high cis-1,4 unit content based on a neodymium phosphate ester

Abstract

A novel two-step synthesis strategy based on a liquid neodymium phosphate ester (Nd(P₅₀₇)₃) catalyst was used to synthesize diene-styrene di-block copolymers with high cis-1,4 unit content, such as butadiene–styrene (PB-b-PS), isoprene–styrene (PI-b-PS), and so on. The strategy not only makes full use of the high cis-1,4 stereo-selectivity of the rare earth catalyst to conjugated dienes, but also adjusts the electron cloud density of the catalytic active center by introducing triphenyl phosphine (PPh₃). Thus, the catalytic activity of the neodymium-based catalyst center toward styrene has been largely improved, and a series of PB/PI-b-PSs with high cis-1,4 unit content (98.3 and 98.1% respectively), narrow molecular weight distribution and controllable block ratio were successfully synthesized. Herein, molecular weight (M_n), molecular weight distribution (M_w/M_n) and microstructure of the block polymers were characterized using SEC-MALLS, FT-IR, ¹H NMR, ¹³C NMR and DSC. The DSC curve of a PB-b-PS with 98.3% cis-1,4 unit and 18.6% polystyrene content shows a T_g of −103.1 °C, which means it has relatively excellent mechanical properties at lower temperature. The results show that these PB/PI-b-PS materials have good application prospects in harsh low temperature environments.