Abstract: A process for the production of pol-(butylene terephthalate) of sufficiently high molecular weight for subsequent extrusion processing without the need of a solid phase post-condensation and at polycondensation pressures greater than now in general use. Polycondensation is carried out in the presence of small amounts of copolymers of an .alpha.-olefin or styrene with free or esterified maleic acid or anhydride.

Abstract: A process for the production of cyclic esters of undecanedioic acid with aliphatic diols comprising thermolyzing the corresponding linear polyesters derived from said acid and said diols under reduced pressure at temperatures of 200.degree.-300.degree. C in the presence of organotin and phosphonate catalysts, wherein the organotin catalyst is of the formula ##STR1## wherein R.sub.1 and R.sub.2 are alkyl of 1-18 carbon atoms, or aryl or aralkyl each of 6-36 carbon atoms, and the phosphonate is O,O-dialkyl-(3,5-di-tert-butyl-4-hydroxybenzyl)-phosphonate, the alkyl groups of which each contain 2-18 carbon atoms.

Abstract: Cyclic esters of dodecanedioic acid with aliphatic diols of 2-12 carbon atoms in the chain and substituted by up to two alkyl of 1-4 carbon atoms, are produced by thermolysis of corresponding linear polyesters under reduced pressure in the presence of catalysts by subjecting the linear polyesters to thermolysis at temperatures between 200.degree. and 300.degree. C., and by utilizing as catalyst a tin(II) salt of an aliphatic monocarboxylic acid of up to 18 carbon atoms, of an aromatic or araliphatic monocarboxylic acid of up to 36 carbon atoms, of an aliphatic or aromatic hydroxy-, poly-, ketocarboxylic acid or of a dicarboxylic acid of up to 18 carbon atoms; or a mixture of an organotin compound of the formula ##STR1## wherein R.sub.1 and R.sub.2 are alkyl of 1-18 carbon atoms, or aryl or aralkyl of 6-36 carbon atoms, and an O,O-dialkyl-(3,5-di-tert.-butyl-4-hydroxybenzyl)-phosphonate wherein each alkyl is of 2-18 carbon atoms.

Abstract: The production of polyester amides based on dicarboxylic acids and/or the esters thereof, primary diamines, and polyhydric alcohols and/or aminocarboxylic acids or lactams, by poly-condensing the mixture under heating in the presence of water, while distilling off the volatile components, and recondensation under reduced pressure is improved so that colorless polyester amides are produced. In a first stage a monomer mixture is preliminarily condensed in the presence of about 3 - 20 percent of water, based on the sum total of the polyamide-forming components, under a pressure of about 14 - 25 bars, at temperatures of about 200.degree. - 300.degree. C and for a time period of about 4 - 12 hours. In a second stage, the mixture is completely condensed, after removal of the water, under a reduced pressure of about 0.01 - 100 mbar at temperatures of about 230.degree. - 300.degree. C and for a period of time of about 1 - 12 hours.