Process for polymerizing poly(lactic acid)

A controlled release matrix dosage form comprising 1% to 75% by weight of a pharmaceutically active ingredient;

• 5% to 50% of a polymer of lactic acid;
• and 1% to 90% of an excipient selected from the group consisting of lactose, dicalcium phosphate, calcium sulfate, sugars, microcrystalline cellulose, gums, methylcellulose, starch, polyvinylpyrrolidone and clay;
• the polymer of lactic acid having a weight average molecular weight of about 2500 to about 4500 and containing less than about 4% lactide;
• and made by the steps of:
• (a) heating lactic acid in a inert atmosphere to about 110.degree. C. at approximately 101 kPa,
• (b) advancing the temperature to about 120.degree. C.,
• (c) maintaining the temperature between about 120.degree. and 140.degree. at a pressure of about 80 kPa a sufficient time to remove about 52% of the theoretical amount of water, and subsequently advancing the temperature to 180.degree. C. to 190.degree. C. while reducing the pressure to about 10 kPa,
• (d) maintaining the temperature and pressure at about 190.degree. C. and 10 kPa for a time sufficient to remove about 92% of the residual water, and
• (e) reducing the pressure to about 400 Pa while maintaining the temperature at least about 180.degree. C. for a time sufficient to remove about 98% of the theoretical water and about 0.5% of the lactic acid as lactide to provide the poly(lactic acid) containing less than about 4% lactide.