Akzo N.v.

Ted Brink

Stephanus A De Graaf

Jacobus J Zeilstra

A copolyetherester comprising a random head-to-tail copolymer of 25-55 percent by weight of short-chain ester units; at least 75 mole percent is composed of 1,4-butylene terephthalate units, and long-chain ester units derived from ethylene oxide-capped poly(propylene oxide) glycol having an ethylene oxide content of from 15-35 percent by weight and a number average molecular weight ranging from 1500-2800. The copolyetherester displays improved physical properties, such as a higher elongation at rupture, notched tensile impact energy and tearing energy, if its relative viscosity (1 g of polymer in 100 g m-cresol at 25.degree. C.) is in the range of 2,45 to 5,0 and the melt index MFI is between ##EQU1## It may be prepared by melt condensation of a copolyetherester having a relative viscosity of 1,8 to 2,5 and subsequently subjecting it to post-condensation in the solid phase for a sufficient period to obtain a polymer corresponding to said viscosity and melt index.

Copolyetherester based on poly (propylene oxide) glycol blocked with

The flame retardancy of a polyethylene terephthalate ester molding composition is improved by mixing therewith both a salt of oxalic acid and polytetrafluoroethylene having a number average molecular weight Mn of more than 10.sup.5. The oxalic acid salt has the formula K.sub.3 [Al(C.sub.2 O.sub.4).sub.3 ], K.sub.2 [Mg(C.sub.2 O.sub.4).sub.2 ] or Rb.sub.3 [Al(C.sub.2 O.sub.4).sub.3 ]. The preferred composition contains from 5-15% by weight of the oxalic acid salt and 0.1-0.5% by weight of polytetrafluoroethylene. The composition having improved flame retardancy may be used to advantage for making shaped articles by injection molding.

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Arnhem, Netherlands

Ted Brink