Synthesis and Thermal Properties of Novel Biodegradable ABCBA Pentablock Copolymers from Poly (Ethylene glycol), L-Lactide and p-Dioxanone

In this work, new biodegradable ABCBA type pentablock copolymers with different mole ratio of L-lactide and PPDO-b-PEG-b-PPDO triblock copolymer were synthesized and characterized. In the first step, PPDO-b-PEG-b-PPDO triblock copolymer was synthesized via a ring-opening polymerization of P-DiOxanone (PDO) monomer with Poly (Ethylene Glycol) (PEG) using stannous octoate (Sn(Oct)2) as the catalyst. In the second step, L-lactide monomers (60 or 80 mole ratio) as the end blocks were added to the resulting prepolymer in presence of stannous octoate (Sn(Oct)2)  catalyst. In the first step, Poly (Ethylene Glycol) (PEG) and, in the second step, triblock copolymer acts as the macro-initiator. The obtained pentablock copolymers were identified by 1H and 13CNMR spectroscopy. Intrinsic viscosity of the resulting copolymers was measured via dilute solution viscometry in chloroform as the solvent. The thermal properties (such as melting points, melting enthalpy and crystallinity) and thermal degradation behavior were studied by Differential Scanning Calorimetry (DSC) and Thermal Gravimetric Analysis (TGA). From the obtained results, it was seen that the poly (L-lactide) end blocks show similar crystallization behavior like poly (L-lactide) homopolymer and also melting temperature of pentablock copolymers rise with an increase in L-lactide content.