Abstract: A process for continuous production of high molecular polybutyleneterephthalate by direct esterification of terephthalic acid and 1,4 butanediol in the presence of tin- or titanium-containing catalysts at preferred temperatures of 235.degree. to 250.degree. C., and preferred pressures of 0.3 to 0.6 bar during the first stage--with minimal formation of tetrahydrofurane--followed by precondensation and polycondensation at reduced pressure.

Abstract: Continuous multistep, economical, energy-saving process for making polybutylene terephthalate in which the butanediol-1,4 used to transesterify dimethyl terephthalate is supplied from the condensed vapors volatilized during the precondensation and polycondensation steps of the process. These vapors, which contain low-soluble esters of terephthalic acid as well as butanediol, are condensed by contact with fresh butanediol, and volatilized butanediol containing the esters is recycled to the initial transesterification stage for reaction with dimethyl terephthalate. No additional butanediol is required for the reaction.

Abstract: Polyethylene terephthalate having an acetaldehyde content of less than 2.5 ppm and suitable for packing of food and beverages intended for human consumption is produced by heating polyethylene terephthalate having an intrinsic viscosity of about 0.5--0.85 at a temperature of 180.degree.-230.degree. C., preferably 200.degree.-220.degree. C., for about 4 to 12 hours. The polyethylene terephthalate must not include more than 25 ppm of ester interchange catalyst or 20 ppm of phosphorous during this heating.

Abstract: A batch process for esterifying ethylene glycol and terephthalic acid at elevated temperature and pressure in which a part of the ethylene glycol required for the complete esterification reaction is placed in an autoclave and heated under pressure, and the remainder of the glycol is added to said heated glycol in the form of a paste with terephthalic acid. Preferably the glycol initially present in the autoclave amounts to 0.3 to 0.8 moles per mole of terephthalic acid while the glycol added as a paste amounts to 1.4 to 0.9 moles per mole of terephthalic acid. The glycol initially in the autoclave may be glycol reclaimed from the mixture volatilized during the reaction and may contain up to 20% water, preferably 2-6% water.

Abstract: A separating or anticaking agent consisting of spherical glass particles having a diameter of 3 to 30.mu. is added to polyester resin granulates to prevent agglomeration during solid state polycondensation in a plug-flow reactor. Thin-walled articles formed from the end product are characterized by high strength, high transparency, crystal clear color, good gas impermeability and a smooth surface.

Abstract: This invention relates to a process for the continuous production of high molecular weight polyethylene terephthalate by polycondensation in the solid phase wherein granulated, dried polyethylene terephthalate, having an intrinsic viscosity of at least 0.15, is first crystallized and is thereafter subjected to solid state polycondensation.