Outstanding controlled release materials were developed using statistically random copolymers of l-lactide (l-LA) with epsilon-caprolactone (CL) using Sn(oct)(2) as a catalyst at 150 A degrees C for 24 h without solvent. Preparation of novel controlled release materials was carried out using useful organic compounds with low boiling points and synthetic random copolymers composed of l-LA and CL as base materials under supercritical carbon dioxide (scCO(2)). Low-boiling-point compounds such as d-limonene, hinokitiol, and trans-2-hexenal were used. In impregnation experiments using scCO(2), the amounts of low-boiling-point compounds increased with an increase in l-LA content. When enzymatic degradation of poly(l-LA-ran-CL) was performed using lipase PS, copolymers with higher CL contents degraded more rapidly than did copolymers with higher l-LA content. In contrast, enzymatic degradation of copolymers occurred to a higher degree with increased l-LA content in enzymatic degradation by proteinase K. In a controlled release experiment with poly(l-LA-ran-CL) (=73/27), after 400 h of degradation by proteinase K, the remaining weight of the copolymer pellet was 6% and the amount of d-limonene remaining in the pellet was 15%.