Polyesters are used in numerous commercial applications such as fibers, films, molded plastics and coatings. The preparation of such products by conventional melt polymerization methods is limited by the high viscosity of the melt.
U.S. Pat. No. 4,613,664 describes a method to prepare high molecular weight polyesters having an intrinsic viscosity greater than 0.9 dL/g wherein monomers from dicarboxylic acids, or esters thereof, and ethylene glycol are polycondensed in specific heating media which may swell the polymers produced. Solvents are specifically excluded in the description of the invention. The patent fails to mention the boiling of the heating medium to remove the low boiling by-product of the polycondensation reaction.
U.S. Pat. No. 3,329,653 describes a process for condensation polymers including polyesters, in which the oligomeric condensation product is heated at reflux temperatures in a liquid non-solvent containing a swelling agent for the polymer. These temperatures, however, are below the melting point of the polymers. The polyester products are unique in that their melting points are significantly higher than corresponding conventional polymers.
USPTO Backgrounds
USPTO Backgrounds