BigPatents India

A process for producing a ply(trimethylene terephthalate) pre;polymer or polyester, comprising contacting, in the presence of a catalyst, terephthalic acid with 1,3-propanediol wherein said catalyst comprises tin and titanium; wherein the tin catalyst is selected from the group consisting of n-butylstannoic acid, octylstannoic acide, dimethyltin oxide, dibutyltin oxide, dioctyltin oxide, diphenyltin oxide, tri-n-butyltin acetate, tri-n-butyltin chloride, tri-n-butyltin fluoride, triethyltin chloride, triethyltin bromide, triethyltin acetate, trimethyltin hydroxide, triphenyltin chloride, triphenyltin bromide, triphenyltin acetate, or combinations of two or more thereof; the titanium catalyst comprises a tetraalky1 titanate; characterized in that the mole ratio of 1,3-propanediol to said acid is in the range of from 1.1:1 to 2.2:1, the tin is present in the amount between 10 to 100 ppm based on the weight of said acid and the titanium is present in the amount of 10 to 200 ppm based on the weight of said acid.