Synthesis and Properties of Amphipathic Poly(D,L-lactide-co-glycolide)-polyethylene glycol-poly(D,L-lactide-co-glycolide) Triblock Copolymers

In this paper, amphipathic poly(d,l-lactide-co-glycolide)-polyethylene glycol-poly(d,l-lactide-co-glycolide) (PLGA-PEG-PLGA) triblock copolymers were synthesized via bulk ring-opening polymerization with d,l-lactide (d,l-LA), glycolide (GA), and polyethylene glycol (PEG) as raw materials and tin(ii) bis(2-ethylhexanoate) (Sn(Oct)2) as catalyst. The synthesis and purification processes were free from organic solvent. The chemical structure of PLGA-PEG-PLGA was characterized by Fourier transform infrared spectroscopy, 1H NMR, gel permeation chromatography, differential scanning calorimetry, and thermo gravimetric analysis. The thermo-sensitivity of PLGA-PEG-PLGA aqueous solution was examined, and the results showed that the copolymers concentration, mass ratio of d,l-LA/GA, and molecular weight of PEG played important parts in controlling the sol–gel transition temperature. The sol–gel transition occurred at lower temperatures with higher copolymer concentrations and mass ratios of d,l-LA/GA. In contrast, the sol–gel transition temperature increased with higher molecular weights of PEG. In vitro drug release studies were carried out using ceftibuten as a model drug. The results indicated that PLGA-PEG-PLGA prepared with 30 wt-% PEG1500 and 70 wt-% PLGA (mass ratio of d,l-LA/GA = 2 : 1) was an effective system for achieving long-sustained controlled release. The drug release from the hydrogel showed a higher initial release followed by a slower pattern up to 120 h, and the mean retention time was ~50 h.