Process for the preparation of a block oligocarbonate

A process for preparing a block oligocarbonate selected from the group consisting of ##STR24## where R denotes ##STR25## and where A denotes an aromatic carbonate structure conforming to ##STR26## where n is 2-6, B is the residue of an aliphatic polyol, with the proviso that said B is bonded to said A through the terminal carboxyl in said A, and where Ar denotes an aromatic radical derived from the group consisting of ##STR27## where A' denotes an C.sub.1-8 alkylene group, C.sub.2-8 alkylidene group, C.sub.5-15 cycloalkylene group, C.sub.5-15 cycloalkylidene group, carbonyl group, an oxygen atom, a sulfur atom, -SO-, -SO.sub.2 - or a radical conforming to ##STR28## e and g denote 0 or 1, Z independently denotes F, Cl, Br or C.sub.1-4 -alkyl, d is an integer of 0 to 4 and f is an integer of 0 to 3, comprising

• a) reacting an aromatic polycarbonate with an aliphatic polyol and
• b) reacting the product of said a) with diphenyl carbonate,
• characterized in that said a) is carried out in the melt at a temperature of 180.degree.-230.degree. C. in the presence of a transesterification catalyst and said polycarbonate having a weight average molecular weight of about 10,000 to 20,000, and where said aliphatic polyol has a molecular weight of up to about 30,000 and a functionality of 1 to 6.