| 摘要 |
PROBLEM TO BE SOLVED: To obtain a process for producing polybutylene terephthalate having a low terminal carboxyl group content, an excellent hydrolysis resistance, and a good hue by maintaining the free specific surface area of a polycondensation reactor in a specified range. SOLUTION: In producing polybutylene terephthalate having an intrinsic vicosity of 0.5 or higher by melt polymn., a batch or continuous polycondensation reactor of which the free specific surface area Sv (cm<2> /cm<3> ) represented by formula I [wherein S is the total specific surface area (cm<2> ) of reactants in the reactor; and V is the total vol.(cm<3> ) of the reactants in the reactor] satisfies the relation represented by formula II wherein [η] is the intrinsic viscosity (dl/g, regarded as dimensionless) of a polymer at the outlet of the reactor; and [COOH] is the terminal carboxyl group content (eq/10<6> g, regarded as dimensionless) of the polymer at the outlet of the reactor} is used to produce polybutylene terephthalate having a carboxyl group content of 30eq/10<6> g or lower.
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