| 摘要 |
PROBLEM TO BE SOLVED: To obtain polybutylene terephthalate excellent in wet heat resistance and hue selecting polybutylene terephthalate which does not contain an alkali or alkaline earth metal, satisfies a specific relation, and has a low terminal carboxyl group content. SOLUTION: This polybutylene terephthalate is produced by melt polymn., has an intrinsic viscosity higher than 0.55, does not contain an alkali or alkaline earth metal, satisfies the relation: [COOH]<=16.5×[η]<0.8> (wherein [COOH] is the terminal carboxyl group content of polybutylene terephthalate; and [η]is the intrinsic viscosity of polybutylene terephthalate), and is obtd. by subjecting an acid ester and a diol in a molar ratio of 1.1-1.6 to transesterification in the presence of a titanium catalyst to a conversion of 75-95%, advancing the condensation at 200-250 deg.C under a vacuum of 300-0.1Torr to a polymn. degree of 15 or higher, and advancing the polycondensation at 230-255 deg.C under a vacuum of 3Torr or lower with a thin-film evaporation means equipped with a rotating disk.
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