Synthesis and characterization of novel biodegradable pentablock copolymers from L-lactide, p-dioxanone and poly (ethylene glycol)

ABCBA type pentablock copolymers, in which the A, B and C blocks are poly (p-Dioxanone) (PPDO), poly (L-Lactide) (PLLA), and polyethylene glycol (PEG), respectively, were synthesized via a two-step ring-opening polymerization in bulk using stannous octoate as the catalyst. PLA-b-PEG-b-PLA Triblock copolymer was synthesized at first and then p-Dioxanone monomers as the other blocks were added to it. In the first step, poly ethylene glycol and, in the second step, triblock copolymer acts as the macro initiator. The obtained copolymers were identified by (1)H, (13)CNMR and IR spectroscopy. The intrinsic viscosity of copolymers was measured in chloroform/phenol (3/1 v/w) solution. The thermal properties, such as melting point, melting enthalpy and crystallinity, were studied. From the results of differential scanning calorimetry and thermal gravimetric analysis, it was observed that the PPDO blocks show similar crystallization behavior like homopolymer and also melting temperature of two PPDO end blocks raise with an increase in DON content in copolymer.