Process for the manufacture of stabilized polyester-polycarbonate copolymers

DETAILED DESCRIPTION What we claim is: 1.
An improved process for the manufacture of thermoplastic polyesters containing carbonate groups and a stabilizer containing phosphorus from linear polyester precondensates which still contain hydroxyl groups, characterized in that linear polyesters containing hydroxyl groups and having a relative viscosity of at least 1.
30, measured at 30.
degree.
C on a 1% strength solution in equal parts of phenol and tetrachloroethane, are allowed to react with 0.
01 to 45% by weight, based on the total amount, of a polycarbonate built up from diols of which the hydroxyl groups are bonded to one or different aromatic radicals and which polycarbonate has a degree of polycondensation of at least 10, in the melt phase or solid phase, at a temperature of 170.
degree.
to 320.
degree.
C and in vacuo, in a stream of inert gas, or in vacuo and a stream of inert gas wherein the improvement comprises increasing the relative viscosity of said thermoplastic polyesters by adding 1 to 15% by weight, based on the polyester precondensate, of a stabilizer containing phosphorus simultaneously with the addition of the polycarbonate.
2.
A process according to claim 1, characterised in that a polyester precondensate is employed which contains at least 80 mol % of terephthalic acid radicals and at least 80 mol % of radicals of an aliphatic diol with 2 to 10 carbon atoms or of 1,4-dihydroxymethylcyclohexane.
3.
A process according to claim 2, characterised in that the aliphatic diol contains 2 to 4 carbon atoms.
4.
A process according to claim 2, characterised in that the polyester precondensate is built up from terephthalic acid and linear alkylenediols with 2 to 4 carbon atoms.
5.
A process according to claim 1, characterised in that the polyester precondensate contains co-condensed diol radicals which possess secondary or phenolic alcohol groups.
6.
A process according to claim 1, characterised in that the polyester precondensate contains at least 50% of hydroxyl end groups, based on the total end groups present