| abstract |
A high molecular weight polyester is disclosed, having a low carboxyl content, and utilizing a low catalyst level, produced by a two-stage process; a melt process until the intrinsic viscosity of the prepolymer reaches about between 0.15 and 0.45 dl/g, and a solid state polymerization in a fluidized bed until the intrinsic viscosity of the polycondensed polymer reaches at least 0.60 dl/g. The melt process employs addition of excess initial glycol, delayed addition of excess glycol, and delayed addition of catalyst, in any combination, to achieve a low carboxyl content polyester prepolymer capable of use in the fluidized bed solid state polymerization. This prepolymer with a minimal carboxyl content achieves a maximum solid state polymerization rate in a fluidized bed. This prepolymer also permits the use of a very low catalyst level to achieve high product purity and still maintains economically satisfactory polymerization rate. Stability and color clarity of the polycondensed product is obtained by this method. |