A facile method to prepare high molecular weight bio-renewable poly(γ-butyrolactone) using a strong base/urea binary synergistic catalytic system

The chemosynthesis of bio-renewable poly(γ-butyrolactone) (PγBL) with a high molecular weight via ring opening polymerization (ROP) of non-strained γ-butyrolactone (γBL) remains a big challenge although several catalysts have been developed in the past two years. In this contribution, we reported the efficient ROP of γBL using a strong base/urea binary synergistic catalytic system. Either an alkaline alkoxide or organophosphazene superbase was used as a strong base in this study. The base/urea binary catalyst showed high catalytic activity and high selectivity for ring opening relative to transesterification toward the ROP of γBL, and the organophosphazene superbase in combination with urea showed better catalytic activity compared to an alkaline alkoxide/urea system. The effects of bases, ureas, and reaction conditions on monomer conversions and resultant molecular weights of PγBL were systematically investigated. A PγBL homopolymer with a high molecular weight up to 35.0 kDa was synthesized using a combination of a cyclic trimeric phosphazene superbase (CTPB) and suitable ureas with electron-donating substituents. The thermal stabilities of PγBL improved dramatically with an increase in its molecular weight. The obtained PγBL exhibited unprecedented superior mechanical properties with an elongation at break of 858 ± 79%, which paves the way for its practical applications.