Synthesis and characterization of ABA type tri-block copolymers derived from p-dioxanone, L-lactide and poly(ethylene glycol)

A series of triblock co-polymers, consisting of a poly(ethylene glycol) (PEG) central block joined to two blocks of random p-dioxanone-co-L-lactide copolymers were synthesized by ring-opening polymerization of p-dioxanone (PDO) and L-lactide (LLA) initiated by PEG in the presence of stannous 2-ethylhexanoate catalyst. The resulting copolymers were characterized by various techniques including ¹H and ¹³C NMR and FTIR spectroscopies, gel permeation chromatography, inherent viscosity, wide-angle X-ray diffractometry (WAXD) and differential scanning calorimetry (DSC). The conversion of PDO and L-lactide into the polymer was studied various mole ratios and at different polymerization temperature from ¹H NMR spectra. Results of WAXD and DSC showed that the crystallinity of PEG macroinitiator was greatly influenced by the composition of PDO and L-lactide in the copolymer. The triblock copolymers with low molecular weight were soluble in water at below room temperature.