Well-defined high molecular weight polyglycolide-b-poly(L-)lactide-b-polyglycolide triblock copolymers: synthesis, characterization and microstructural analysis

Block copolymerization is already a proven technique to manipulate the properties of polymeric materials. Herein, our work presents a facile synthesis of high molecular weight polyglycolide-b-poly(L-)lactide-b-polyglycolide (b-PLLGA) triblock copolymers by ring-opening polymerization (ROP) in bulk at considerably low temperature. A series of ABA-type triblock copolymers was successfully prepared and microstructural properties were thoroughly investigated against random copolymers of poly(L-lactide-co-glycolide) (r-PLLGA). This synthesis method led to the preparation of high molecular weight b-PLLGAs with highly defined chain microstructure and an intrinsic viscosity [η] was obtained as high as 1.62 dl/g when [M]:[I] was [1]:[1000]. The investigations revealed that the prepared copolymers are in block type chain microstructure, having exclusive thermal transitions and sequence/segment properties. DSC analysis revealed that two glass (Tg) transitions and two melt transitions (Tm) exclusively associated to PGA block and PLLA block. Results were further confirmed by homosequenses of –LLLL- and -GGGG- from 13C-NMR spectroscopy. Tensile results revealed that b-PLLGA have higher tensile strength and Young’s modulus as compared to r-PLLGA. Moreover, b-PLLGAs are more thermally stable and have a wider thermal processing window.