Synthesis of poly(p-dioxanone)-based block copolymers in supercritical carbon dioxide

Poly(p-dioxanone)-poly(ethylene glycol)-poly(p-dioxanone) triblock copolymers (PPDO-PEG-PPDO) were first synthesized by suspension ring-opening polymerization (ROP) of p-dioxanone (PDO) in supercritical carbon dioxide (scCO(2)) using different molecular weights (2-10 K) of poly(ethylene glycol) (PEG) as macroinitiators. White and fine flow powders were successfully obtained when the molecular weight of PEG was below 6 K and its feed content below 20 wt.%. The H-1 nuclear magnetic resonance (NMR) result indicated the formation of PPDO-PEG-PPDO block structure even in a confined polymerized environment of particles. All the powderous samples contained irregular shaped particles that were observed by scanning electron microscope (SEM). Except for the copolymer with 10 wt.% PEG10K feed content, the mean particle sizes of other powderous samples showed identical values close to 15 mu m. This fact was in agreement with the crystallinity of PPDO in the copolymers measured by differential scanning calorimetry (DSC). The water absorption of these copolymers was also measured, and as compared with PPDO homopolymer, the introduction of PEG increased the water absorption of the copolymers. The green and environmentally friendly method disclosed in this work is attractive to directly synthesize biodegradable polymeric particles with potential biomedical applications.