Polycarbonates and the use thereof for the preparation of bioerosible matrices

The method of preparation of a polycarbonate of formula (I) ##STR9## wherein a is an integer from 2 to 300;

• R.sup.1 and R.sup.2 are the same or different, and are independently a polyester residue of formula (III) ##STR10## wherein x and y are integers from 0 to 50, R.sup.4 and R.sup.5, which are the same or different and are aliphatic straight or branched hydrocarbon chains having from 1 to 4 carbon atoms, R.sup.6 is an aliphatic or alicyclic straight or branched chain having from 2 to 18 carbon atoms, or a polyoxyalkylene residue of formula (II) ##STR11## to which R.sup.3 is hydrogen or methyl, n is an integer from 1 to 3 and m is an integer from 1 to 200, and said two groups --R.sup.4 --COO and --R.sup.5 --COO are randomly distributed in the polyester residue, x and y being in any ratio from 0 to 100, which consists of the steps of
• 1) reacting 2 moles of 1,1.sup.1 -carbonyldiimidazole with a diol of formula (IV) or (V)
• HO--R.sup.1 --OH (IV)
• HO--R.sup.2 --OH (V)
• wherein R.sup.1 and R.sup.2 are as defined hereinabove, in an organic aprotic solvent which is a member selected from the group consisting of chloroform, acetonitrile, dimethylsulfoxide, and dimethylformamide, at a temperature from room temperature to the boiling temperature of the reaction mixture, whereby a diimidazole formate of formula VI or VII is obtained, ##STR12## wherein R.sup.1 and R.sup.2 are the same as hereinabove;
• and 2) then reacting said compound of formula VI or VII with a diol of formula (IV) or (V)
• HO--R.sup.1 --OH (IV)
• or
• HO--R.sup.2 --OH (V)
• wherein R.sup.1 and R.sup.2 are the same as hereinabove, with imidazole in an organic aprotic solvent followed by extraction with water, drying said solvent and recovering said polycarbonate of formula (I) by evaporation of said organic aprotic solvent.