Branched polycarbonates containing tetracarboxyfunctional heterocyclic compounds and process for their preparation

Process for the preparation of thermoplastic, blow moldable, branched polycarbonate derived from at least one aromatic dihydroxy compound, phosgene, and aliphatic polyfunctional acid branching agent compound having the formula:

• ##STR4## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are the same or different from each other, and represent --COOH or COCL;
• X is O or S or the corresponding saturated compounds, comprising the following steps carried out successively:
• (a) preparing a chloroformyl-capped oligomer, by reacting phosgene and a dihydroxyaromatic compound, corresponding to the formula:
• ##STR5## wherein:
• R represents substituted or unsubstituted alkylene radical, containing from 0 to 5 carbon atoms, --O-- or --S-- atoms, --SO.sub.2 -- or --CO-- groups;
• x, y are the same or different from each other, and represent H, CH.sub.3, halogens;
• m and n are integers, the same or different from each other, within the range of from 1 to 4;
• (b) condensing the so-obtained oligomer with said aliphatic polyfunctional acid branching agent compound of formula (I), wherein R.sub.1, R.sub.2, R.sub.3, and R.sub.4, X have the above meaning;
• (c) adding a dihydroxyaromatic compound (II) to the mixture resulting from (b) and polycondensing said mixture;
• and
• (d) recovering the branched polycarbonate from the reaction mixture.