Release of model compounds from modified lactone copolymers

The applicability of three different P(ϵ‐caprolactone‐co‐DL‐lactide) copolymers for injection‐molded controlled release devices was evaluated. The copolymers of ϵ‐caprolactone and DL‐lactide were polymerized in bulk using Sn(II) octoate as the catalyst. Glycerol, polyethylene glycol 1000, and polyethylene glycol 4000 were used as initiators. Copolymers were characterized by size exclusion chromatography, differential scanning calorimetry, and nuclear magnetic resonance spectroscopy measurements. The release of two model compounds, theophylline and propranolol hydrochloride, at different loadings (2–30 wt %) was studied. The solubility of the model compounds into the matrices was confirmed to be low by DSC measurements. Increasing the hydrophilicity of the copolymer matrix increased the release rates of both model compounds. The results clearly demonstrate that the desired release rates of these model compounds can be tailored by varying the compound loading or modifying the hydrophilicity of the matrix copolymer. The copolymers were found to be relatively stable during the 4‐month hydrolysis. Addition of hydrophilic polyethylene glycol blocks into the backbone of the copolymer chain increased water absorption and thus the degradation was faster. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2118–2126, 2001