PROBLEM TO BE SOLVED: To provide a lactic acid polymer useful as a matrix for sustained-release preparation which can fully suppress the initial excessive release of a physiologically active substance from microcapsules encapsulating a physiologically active substance and can keep a stable release rate of the physiologically active substance over a long period of time.SOLUTION: A process for producing the lactic acid polymer having a weight-average molecular weight of 15,000 to 50,000, in which the content of a polymer having a weight-average molecular weight of nearly 5,000 or less is nearly 5 wt.% or less, is characterized in that the high-molecular weight lactic acid polymer is hydrolyzed, a solution containing a hydrolyzed product thus obtained is placed under conditions where the objective lactic acid polymer contained in the solution can be precipitated, and the precipitated lactic acid polymer is separated and collected. There are also provided the lactic acid polymer having a weight-average molecular weight of 15,000 to 50,000, in which the content of a polymer having a weight-averaged molecular weight of 5,000 or less is nearly 5 wt.%, the matrix for sustained release preparation containing the lactic acid polymer, and use as the matrix for sustained release preparation of the lactic acid polymer.COPYRIGHT: (C)2012,JPO&INPIT【課題】生理活性物質を取り込んだマイクロカプセルからの生理活性物質の初期過剰放出を十分に抑制し、且つ長期に亘りその放出速度を安定に保ち得る徐放性製剤用基材として有用な乳酸重合体を提供すること。【解決手段】高分子量の乳酸重合体を加水分解し、得られた加水分解生成物を含む溶液を、そこに含有される目的とする乳酸重合体が析出し得る条件下に置き、析出物を分離、取得することを特徴とする、重量平均分子量約5000以下の重合体含有量が約5重量%以下である、重量平均分子量15000~50000の乳酸重合体の製造方法、重量平均分子量5000以下の重合体含有量が約5重量%以下である、重量平均分子量15000~50000の乳酸重合体、当該乳酸重合体を含んで成る徐放性製剤用基材、及び当該乳酸重合体の徐放性製剤用基材としての用途。【選択図】なし
