In this article, we cover the development of L-lactide (L-LA) random copolymers into which useful compounds, such as repellents and antibacterial agents, were impregnated by high concentration. Outstanding controlled release materials were developed with statistical random copolymers of L-LA with cyclic carbonate (CC) [2,2-dimethyltrimethylene carbonate (2,2-DTMC) or tetramethylene carbonate (TEMC)] with tin 2-ethyL-hexanoate as a catalyst at 150 degrees C (2,2-DTMC) or 120 degrees C (TEMC) for 24 h without solvent. The preparation of improved controlled release materials was performed with useful organic compounds with low boiling points and synthetic L-LA random copolymers containing CCs as base materials under supercritical carbon dioxide (scCO(2)). Low-boiling-point compounds, such as d-limonene and hinokitiol, were used. In impregnation experiments with scCO(2), the amounts of low-boiling-point compounds increased with increasings L-LA content. The compound content impregnated into poly(L-lactide-ran-cyclic carbonate) [poly(L-LA-ran-CC)] was greater than that of the experiment with poly(L-lactide-ran-e-caprolactone) previously studied. When the enzymatic degradation of poly(L-LA-ran-CC) was performed with proteinase K, copolymers with a greater L-LA content degraded more rapidly than did copolymers with a greater CC content. In a controlled release experiment with poly(L-lactide-ran-2,2-dimethyltrimethylene carbonate) (76/24) or poly(L-lactide-ran-tetramethylene carbonate) (81/19), the rate of polymer degradation and the rate of impregnated compound release were almost the same. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 1431-1441, 2011