Synthesis and characterization of biodegradable A-B-A triblock copolymers containing poly(ε-caprolactone) A blocks and poly(frans-4-hydroxy-L- proline) B blocks

Novel, biodegradable poly(ε-caprolactone)-block-poly(trans-4-hydroxy- N-benzyloxycarbonyl-L-proline)-block-poly(ε-caprolactone) triblock copolymers were synthesized by ring-opening polymerization from dihydrozyl-terminated macroinitdator poly(trans-4-hydroxy-N-benzyloxycarbonyl-L- proline) (PHpr) and ε-caprolactone (ε-CL) with stannous octoate as the catalyst. The molecular weights were characterized with gel permeation chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. With an increase in the contents of ε-CL incorporated into the copolymers, a decrease in the glass-transition temperature (T _g) was observed. The T_g values of copoly(4-phenyl-ε- caprolactone) and copoly(4-methyl-ε-caprolactone) were higher than T _g of copoly(ε-caprolactone). Their micellar characteristics in an aqueous phase were investigated with fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. The block copolymers formed micelles in the aqueous phase with critical micelle concentrations in the range of 1.00-1.36 mg L^-1. With higher molecular weights and Hydrophobie components in the copolymers, a higher critical micelle concentration was observed. As the feed weight ratio of antitriptyline hydrochloride (AM) to the polymer increased, the drug loading increased. The micelles exhibited a spherical shape, and the average size was less than 260 nm. The in vitro hydrolytic degradation and controlled drug release properties of the triblock copolvmers were also investigated.