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 [eta] 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 (T-g) transitions and two melt transitions (T-m) exclusively associated to PGA block and PLLA block. Results were further confirmed by homosequenses of -LLLL- and -GGGG- from C-13-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.