Thermogelling poly(,epsilon-caprolactone-co-D,L-lactide)-poly(ethylene glycol)poly(epsilon-caprolactone-co-D,L-lactide) and poly(E-caprolactone-CO-L-lactide)-poly(ethylene glycol)-poly(P.-caprolactone-CO-L-lactide) triblock copolymers were synthesized through the ring-opening polymerization of e-caprolactone and D,L-lactide or L-lactide in the presence of poly(ethylene glycol). The polymerization reaction was carried out in 1,3,5-trimethylbenzene with Sn(Oct)(2) as the catalyst at various temperatures, and the yields were about 96%. The molecular weights and polydispersities (M-w/M-n) by gel permeation chromatography were in the ranges of 5140-6750 and 1.35-1.45, respectively. The differential scanning calorimetry results showed that the melting temperatures of the poly(g-caprolactone) components were between 30 and 40 degrees C. By the subtle tuning of the chemical compositions and microstructures of these triblock copolymers, the aqueous solutions underwent sol-gel transitions as the temperature increased, with the suitable lower critical solution temperature in the range of 1728 degrees C at different concentrations. Transesterification in the polymerization process generated the redistribution of sequences, which remarkably affected the sol-gel transition temperature. The amphiphilic copolymers formed micelles in aqueous solutions with a diameter of 62 nm and a critical micelle concentration of about 0.032 wt % at 20 degrees C. Micelles aggregated as the temperature increased, leading to gel formation. The sol-gel transition was studied, with a focus on the structure-property relationship. It is expected to have potential applications in drug delivery and tissue engineering.