Study On The Doto Catalysis In The Preparations Of PBT By Direct Esterification Method

Polybutylene terephthalate is a kind of thermoplastic resin with excellent performance, it is also the fifth big engineering plastics after the PA, PC, POM and MPPO. PBT not only has the advantages such as low glass transition temperature, fast crystallization rate and good molding performance, but also possesses high heat resistance, high mechanical strength, high electrical insulation, chemical corrosion resistance, aging resistance and low friction properties. At present, PBT has been used in the manufacture of electronic appliances, auto parts, machinery equipment and precision parts, to replace metal materials, thermosetting plastics and some thermoplastics. Although the demand for PBT is growing increasingly throughout domestic market, the manufacture of the PBT can not meet the consumption. So far, there are mainly two methods for the preparation of PBT, ester exchange method and direct esterification method, ie. the reaction of dimethyl terephthalate (relative to DMT method) or terephthalic acid (relative to PTA method) with butanediol in the presence of catalyst. In China, the manufactures of PBT is mainly by imported technology such as Zimmer’s as well as Hitachi’s process. The catalyst are Titanium compounds. But there’s a problem that Titanium catalyst is easy to hydrolyze to form solid oxide in PBT production, especially in the process using direct esterificaton method. It has a important theoretical significance and practical application significance to expand PBT catalysts, improve the stability of the production process, improve the quality of products and increase the competitiveness in market.The preparations of polybutylene terephthalate (PBT) by direct esterification with catalysts by Ti or Sn compound were studied. It is found for the the first time that Dioctyltin oxide (DOTO) could be successfully applied in the preparations of PBT. The effects of different reaction parameters on the raction process have been investigated with DOTO as the catalyst, and at the same time, properties of the product were characterized. The result showed that, under the optimal reaction conditions:catalyst amount:DOTO10-3J(DOTO/PTA, mass ratio), molar ratio of acid to alcohol:1:1.7, esterification temperature:230℃, esterification time:3h, condensation temperature:245℃, condensation time:5h, PBT can be prepared successfully. The PBT product has a melting point range between228-230℃and intrinsic viscosity of0.789dL/g. number average molecular30000. It meets the requirement of PBT engineering plastics.