Release of model compounds from modified lactone copolymers

The applicability of three different P(epsilon -caprolactone-co-DL-lactide) copolymers for injection-molded controlled release devices was evaluated. The copolymers of epsilon -caprolactone and DL-lactide were polymerized in bulk using Sn(II) octoate as the catalyst. Glycerol, polyethylene glycol 10 00, and polyethylene glycol 4000 were used as initiators. Copolymers were c haracterized by size exclusion chromatography, differential scanning calori metry, and nuclear magnetic resonance spectroscopy measurements. The releas e of two model compounds, theophylline and propranolol hydrochloride, at di fferent loadings (2-30 wt %) was studied. The solubility of the model compo unds into the matrices was confirmed to be low by DSC measurements. Increas ing the hydrophilicity of the copolymer matrix increased the release rates of both model compounds. The results clearly demonstrate that the desired r elease rates of these model compounds can be tailored by varying the compou nd loading or modifying the hydrophilicity of the matrix copolymer. The cop olymers were found to be relatively stable during the 4-month hydrolysis. A ddition of hydrophilic polyethylene glycol blocks into the backbone of the copolymer chain increased water absorption and thus the degradation was fas ter. (C) 2001 John Wiley & Sons, Inc.