Studies on the synthesis of poly(1,4-butyleneterephthalate) by the direct polycon densation and its properties. (Part 3) Polycondensation of poly(1,4-butyleneterephthalate) prepolymer.

Polycondensation reaction conditions of poly (1, 4-butyleneterephthalate) (PBT) prepolymer obtained by direct esterification of terephthalic acid (TA) with butanediol-1, 4 were investigated. It was found that1) the amount of tetrahydrofurane formed as a by-product decreases with lowering the conversion of TA at the esterification stage, while the ultimate molecular weight of PBT obtained decreases with lowering the conversion.2) the optimum reaction temperature is lower than that in the synthesis of other poly (alkylene terephthalates).3) the catalyst is favorably added at stages of both initial esterification and subsequent polycondensation, although its total concentration does not affect an ultimate molecular weight of the resulting PBT.To obtain the Mark-Houwink-Sakurada viscosity equation of PBT in o-chlorophenol at 25°C, the samples having the molecular weight in the range from 8, 400 to 67, 000 were prepared and the following viscosity equation was obtained: