Catalytic compositions for the preparation of poly(butylene terephthalate)

A process for the preparation of poly(butylene terephthalate) from dimethyl terephthalate and butylene glycol comprising the steps of:

• (a) preparing a catalyst composition containing:
• (a) a titanium compound primary catalyst, from about 0.01 PHR to about 1 PHR wherein said titanium compound primary catalyst is tetrabutyl titanate or tetra(isopropyl) titanate;
• and
• (b) an alkali metal phosphate or alkali metal phosphite co-catalyst, from about 0.001 PHR to about 1 PHR;
• wherein PHR represents parts of said primary catalyst or said co-catalyst per hundred parts, by weight, of the theoretical value of said poly(butylene terephthalate) resin to be produced);
• (b) placing said catalyst composition, said dimethyl terephthalate and said butylene glycol in a reaction vessel, said butylene glycol being in excess relative to said dimethyl terephthalate;
• (c) raising reaction temperature to about 200.degree..about.280.degree. C. to start a transesterification reaction;
• (d) raising reaction temperature to about 240.degree..about.300.degree. C. and applying vacuum in said reaction vessel to start a polymerization reaction;
• and
• (e) removing unreacted butylene glycol from reaction product to obtain said poly(butylene terephthalate).