Patent ID: 8198392

Claim:
A polymer producing method comprising stirring polyhydroxycarboxylic acid in a molten state obtained by subjecting a cyclic dimer of hydroxycarboxylic acid to a ring opening polymerization reaction and removing by degassing an unreacted cyclic dimer residue at a pressure lower than that for the ring opening polymerization reaction, wherein the ring opening polymerization reaction is continuously carried out using a plurality of polymerization tanks connected in series, provided that a horizontal polymerization tank, which comprises a horizontal reaction tank accommodating a stirring body having a stirring shaft located horizontally with respect to the ground, a supply port that is formed at one end side of the horizontal reaction tank for supplying a reactant, a discharge port that is formed at the other end side of the horizontal reaction tank for discharging the reactant, and at least one weir placed in the horizontal reaction tank, is placed in the first stage, and that a vertical polymerization tank, which comprises a vertical reaction tank accommodating a stirring shaft located vertically with respect to the ground, a supply port that is formed at the upper end side of the vertical reaction tank for supplying a reactant, and a discharge port that is formed at the lower end side of the vertical reaction tank for discharging the reactant, is placed in the final stage; and wherein the removal by degassing is continuously carried out by supplying a treated substance obtained by the ring opening polymerization reaction via the supply port located at the one end side of the horizontal tank, allowing the stirring body, which comprises a plurality of rectangular stick frames coupled to oriente longitudinally with respect to the tank and does not have a stirring shaft inserted through the virtual rotation center, to rotate circumferentially within the tank, discharging the treated substance from the discharge port located at the other end side, and discharging a degassed gas via a degassing port located above the molten liquid level of the treated substance.