Abstract: A process for forming polyesters that comprises the steps of esterifying a terephthalic acid and an ethylene glycol to produce an esterification product containing a bis (betahydroxyethyl) terephthalate, and continuously polycondensing the obtained esterification product to form a polyester. In both the esterifying step and the polycondensing step, a reaction catalyst consisting of a compound of antimony and a compound of titanium is used. The weight ratio of the compound of antimony to the compound of titanium is 0.01 to 100. The process of the present invention can considerably reduce both the esterification time and the polycondensation time and provides good color, reduced diethylene glycol content and reduced condensation of terminal carboxyl groups in the resulting polyesters.

Abstract: A method for forming polyesters (polyethylene terephthalate, PET) having a high degree of polymerization with improved color and lower diethylene glycol (DEG) content in a shorter period of time than in known methods. The method according to the invention comprises forming oligomers from ethylene glycol and terephthalic acid by esterification, forming prepolymers having a degree of polymerization ranging from 10 to 50 by polycondensing the resulting oligomers for an optimum time, forming polyesters by polycondensing the oligomers and the prepolymers in a weight ratio ranging from 1:0.1 to 1:90, thereby providing polyesters of improved color and low DEG content in a short time.

Abstract: This invention relates to processes for the preparation of polybutylene terephthalate based polymer, which processes produce polymer having excellent color, a small amount of side-product and a high degree of polymerization within a short time. Complex catalyst which is employed comprises antimony compounds and titanium compounds, optionally together with phosphorous based compounds and hindered phenolic, and the catalyst decreases the phenomena that conventional catalysts of tin and titanium based compounds have of making the polymer colored by declining hydrolyzation and heat-stability. The catalyst also decreases the amount of side-product, THF sharply. As a result, improved polybutyleneterephthalate can be prepared.