Key Words:Polycarbonate; Phosphonium borane Lewis pair; CO2 utilizationOrganocatalysisRing-opening polymerization
Abstract:Well-defined polycarbonate diol was successfully synthesized through a strategy using a combination of organocatalyst and water.Such strategy was less developed in organocatalyzed polymerization and frequently regarded as side reactions. Herein, one-component phosphonium borane Lewis pairs PB1-PB8 were successfully applied in the copolymerization of CO_2 and cyclohexene oxide(CHO) to generate poly(CHO-alt-CO_2) carbonate(PCHC). Parameters of linker length and counter anion effects on the catalyst activity were investigated. It was found that Lewis pair PB3 served as a dual initiator and catalyst in the copolymerization of CHO and CO_2 with or without the presence of water. In contrast, Lewis pair PB8 can serve as a true catalyst for the preparation of well-defined α,ω-hydroxyl PCHC diols. This was achieved by introducing a labile CF_3COO group as counter anion through anion exchange reaction while water molecules acted as chain transfer agents. The function of trifluoroacetate group in the polymerization process was investigated in detail and possible mechanism was proposed. Upon changing the amount of water and catalyst loading, PCHC diols with ied molecular weight(1.5 kg/mol to 7.5 kg/mol), low dispersities(D<1.2) and carbonate content(>99%) could be easily obtained. The low molecular weight PCHC diol was used as a bifunctional macroinitiator for the ring-opening polymerization of L-lactide(LLA) to afford ABA triblock copolymer in one-pot synthesis.
Volume:v.41
Issue:05
Translation or Not:no