A wide range of poly(glycolic acid)-based di- and tri-block polyesters by a single organocatalyst: Synthesis and characterization

The ring-opening polymerization (ROP) of glycolide (GA), the copolymerization of GA with ε-caprolactone (ε-CL), and the terpolymerization of GA with ε-CL and lactide (LA) were studied over the cheap non-toxic metal-free organocatalyst tetrabutylammonium 2-(carbamyl)benzoate (TBACB). The catalyst with comparable catalytic activity to the comonomers afforded a series of well-defined PGA-based block polymers with ε-CL, LA monomers at high yields by varying feeding methods under bulk and solution conditions. The poly(ɛ-caprolactone-b-glycolic acid)s (PCGAs) and poly(ε-caprolactone-b-lactide-b-glycolide) (PCLGAs) with controllable chain segment composition were obtained by “one-pot” solution copolymerization in mixtures, or semi-batch copolymerization. Due to the high thermal stability of TBACB, the PCGA and PCLGA with high molecular weight (M_n = 6.9 and 10.0 kg mol⁻¹) could also be obtained by bulk polymerization at 120 °C by sequential addition of ε-CL, (LA), and GA in a short time (<2.5 h). Compared to the polymers with similar compositions by different methods, the bulk polymerization showed more effective and higher molecular weight. The microstructure characterized by NMR showed highly ordered block polymers with defined chain segments. Two melting transitions (T_m) of PCGA suggested exclusively associated with PCL and PGA segmental chain in the product.