The invention provides methods for the formation of thermo-reversible hydrogels from triblock copolymers of poly(ethylene glycol) and poly(α-benzyl carboxylate-ε-caprolactone) (PBCL-PEG-PBCL) prepared by bulk and solution polymerization. PBCL-PEG-PBCLs prepared at fixed PBCL to PEG ratios but different polymerization times were characterized for their average molecular weights, molar-mass disparity and intrinsic viscosity using .sup.1H NMR and gel permeation chromatography (GPC). The results indicated a copolymer of high molecular weight population with elevated intrinsic viscosity. The size and proportion of this population grew as a function of polymerization time. The formation of this high molecular weight PBCL-PEG-PBCL population can be attributed to non-linear architecture caused by partial cross-linking of the PBCL segment during the polymerization reaction. At least about 40% mole concentration of the high molecular weight PBCL-PEG-PBCL was required for thermo-reversible micellar aggregation in aqueous media and hydrogel formation.