Synthesis of sustainable polyesters via metal-free catalyzed ROP of cyclic esters is of great importance for their biomedical applications, and is therefore becoming the most appealing research topic in polymer synthesis. As a category of organic superbases, phosphazene exhibits high catalytic activity in ROP of cyclic esters. The catalytic performances of phosphazene catalysts highly depend on their structure and basicity. Herein, a new superbase, cyclic trimeric phosphazene base (CTPB), was prepared with high yield and purity (Scheme 1). In the presence of alcohol, the CTPB can serve as highly efficient organocatalyst for ROP of “non-strain” five-membered γ-butyrolactone to offer well-defined poly(γ-butyrolactone) with high conversions. The produced polymers have high molecular weights and low molecular distributions (1.27-1.50). NMR analysis of initiation process and the structural analysis of resulted polymers by MALDI-TOF suggest an activating initiator mechanism.<br/>On the other hand, the preparation of block copolymers containing poly(γ-butyrolactone) block remains as a synthetic challenge owing to the unfavorable thermodynamics towards the ROP of “non-strain” five-membered ring. Using CTPB superbase as catalyst, we realized the successful one-pot preparation of poly(γ-butyrolactone)-b-poly(L-lactide) by sequential ROP of γBL and L-LA for the first time. The thermal stabilities, crystallization and melting behaviors of the obtained diblock copolyesters were also investigated.

Synthesis of sustainable poly(γ-butylactone) and copolymers by cyclic trimeric phosphaze base catalyzed ROP

256th National Meeting (2018)

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