Abstract: A method for producing a high molecular weight aliphatic polyester, wherein:(A) 100 parts by weight of polyester (a) with a number average molecular weight of at least 10,000, and a weight average molecular weight of at least 30,000, and with end-groups that are substantially hydroxyl groups, and with a melting point of at least 60.degree. C., the polyester (a) having been obtained by reacting the following three ingredients: (i) a glycol ingredient; (ii) an aliphatic dicarboxylic acid ingredient; and (iii) a trifunctional or tetrafunctional ingredient reacts with(B) 0.1-3 parts by weight of a poly-isocyanate in a melted state of the polyester (a).The method provides a high molecular weight aliphatic polyester which has good properties and a melt viscosity required for molding and forming and has a wide molecular weight distribution. The high molecular weight aliphatic polyester is applicable to a variety of fields, such as films, moldings and formings, fibers, etc.

Abstract: A method for manufacturing a biodegradable high molecular weight aliphatic polyester. This method comprises the steps of: [A] synthesizing an aliphatic polyester having a number average molecular weight of at least 5,000 and/or a weight average molecular weight of at least 30,000 by reacting aliphatic or alicyclic glycol with aliphatic dicarboxylic acid or its anhydride, applying a 0.001-0.5 part by weight of organic or inorganic metallic compound as a catalyst with respect to 100 parts by weight of aliphatic polyester to be produced; [B] adding a 0.01-3 parts by weight of organic or inorganic phosphorus compound with respect to 100 parts by weight of aliphatic polyester upon completion of the reaction; and [C] reacting a 0.1-5 parts by weight of polyvalent isocyanate compound with 100 parts by weight of the aliphatic polyester so that the polyester has a number average molecular weight of at least 10,000 and/or a weight average molecular weight of at least 50,000.