Aliphatic polyester and process for producing the same

Abstract

An object of the present invention is to provide an aliphatic polyester which is produced as a high-molecular-weight one without using a chain extender such as an isocyanate compound or a carbonate compound and is excellent in moldability in injection molding, blow molding, or extrusion molding, thermal stability, and mechanical properties such as tensile properties. The invention relates to an aliphatic polyester comprising an aliphatic diol unit, an aliphatic dicarboxylic acid unit, and a unit of an organic acid having a pKa value of 3.7 or below at 25° C., wherein a content of a carbonate bond contained in the polyester is less than 1 mol %, a content of a urethane bond is less than 0.06 mol %, a content of an aliphatic monooxymonocarboxylic acid unit is less than 0.02 mol %, a content of the phosphorus atom derived from a phosphorus compound selected from among organic phosphinic acids, organic phosphonic acids, and hydrogen phosphate salts is less than 10 −9 mol %, based on the whole monomer units constituting the polyester, and a reduced viscosity (ηsp/C) is 1.6 or more.

1 . An aliphatic polyester having a retention rate of the reduced viscosity of 80% or more when the aliphatic polyester is transformed into a film-shape test piece having 150±25 μm and the test piece is kept under conditions of a temperature of 50° C. and a relative humidity of 90% R.H. for 28 days.  
     
     
         2 . The aliphatic polyester according to  claim 1 , which comprises an aliphatic diol unit, an aliphatic dicarboxylic acid unit and a unit of an organic acid having a pKa value of 3.7 or below at 25° C., the polyester having a carbonate bond content of less than 1 mol %, an aliphatic monooxymonocarboxylic acid unit content of less than 0.02 mol %, phosphorus atom content of less than 10 −9  mol %, as derived from a phosphorus compound selected from the group consisting of an organic phosphinic acid, an organic phosphonic acid, and a hydrogen phosphate salt, based on all the monomer units which constitute the polyester, and the polyester having a reduced viscosity (ηsp/C) of 1.6 or more.  
     
     
         3 . The aliphatic polyester according to  claim 1 , wherein the unit content of the organic acid having a pKa value of 3.7 or below at 25° C. ranges from 0.0001 to 0.4 mol %, based on the aliphatic dicarboxylic acid unit.  
     
     
         4 . The aliphatic polyester according to  claim 1 , wherein the aliphatic diol unit is an ethylene glycol unit and/or a 1,4-butanediol unit.  
     
     
         5 . The aliphatic polyester according to  claim 1 , wherein the aliphatic dicarboxylic acid unit is adipic acid and/or succinic acid.  
     
     
         6 . The aliphatic polyester according to  claim 1 , wherein the unit of the organic acid having a pKa value of 3.7 or below at 25° C. is at least one selected from the group consisting of malic acid, tartaric acid, maleic acid, and fumaric acid.  
     
     
         7 . The aliphatic polyester according to  claim 1 , wherein the number of terminal COOH groups in the aliphatic polyester is 50 eg/ton or less.