The present invention relates to polycarbonates of formula (I)

wherein a is an integer from 2 to 300j - R 1 and R2, which can be the same or different, are an aliphatic or alicyclic straight or branched chain having from 2 to 18 carbon. atoms, or R 1 and R2 are a polyoxyalkylene residue of formula

in which R is hydrogen or methyl, n is an integer from 1 to 3 and m is an integer from 1 to 200, or a polyester residue of formula (III)

where , which can be the same or different, are aliphatic straight or branched hydrocarbon chains having from 1 to 4 carbon atoms, R is an aliphatic or alicyclic straight or branched chain having from 2 to 18 carbon atoms, or a polyoxyalkylene residue of formula (II), being intended that the two groups -R 4-COO and -R5-COO are randomly distributed in the polyester residue, x and y being in any possible ratio from 0 to 100.

When R1 and/or R2 are alkylene chains, these preferably have from 2 to 12 carbon atoms.

When R 1 and/or R2 are polyoxyalkylene residues, these are preferably polyoxyethylene residues of ffoorrmmuullaa ((IIII)) wwhheerreeiinn R is H, n is 1 and is an integer from 2 to 100.

Polycarbonates in which R 1 and R2 are hexylene, decylene, dodecylene, 1,4-cyclohexylene, 2,2-dimethyl- 1,3-propylene, 2,5-dim th 1-2,5-hexylene or polyoxy- ethylene residues are preferred.

Particularly preferred are those polycarbonates in which R 1 and R2 are selected from 1,4-cyclohexylene,

2,2-dimethyl-l,3-propylene, 2,5- imeth 1-2,5-hexylene or polyoxyethylene residues. More particularly preferred are those polycarbonates in which R 1 and R2 are polyester residues.

Most particularly preferred are those polycarbona- tes in which R 1 and R2 are polyester residues, wherein R 4 and R5 are methylene or methyl-methylene. Groups R 1 and R2 are preferably different from each other so as to give alternate co-polycarbonates, i.e. having regularly alternated monomeric units.

The invention further relates to a process for the preparation of compounds I and the use thereof for the preparation of pharmaceutical formulations slowly releasing the active principles.

Examples of pharmaceutical formulations in which the drug (active principle) is incorporated in a polymer matrix are well known in literature: See

"Biodegradable Polymers as Drug Delivery Systems", ed.

by M. Chasin and R. Langer, Marcel Dekker Inc., New York 1990; "Methods in Enzymology, Vol. 112, Drug and Enzyme Targeting, Part A", ed. by K.J. Widder and R. Green, Academic Press, Inc., Orlando, Florida 1985; "Formes Pharmaceutiques Nouvelles", P. Buri, F. Puisieux, E. Doelker and J.P. Benoit, Technique et Documentation (Lavoisier) , Paris 1985; "Biodegradable Polymers for controlled release of peptides and proteins", F.G. Hutchison and B.J.To. Furr, in Drug Carrier Systems, F.H.D. Roerdink and A.M. Kroom eds. , John Wiley and Sons, Chichester, 1989; and "Controlled Release of Biologically Active Agents" by Richard Baker, John Wiley and Sons, New York 1987.

Aliphatic polycarbonates are known for example from DE 2546534, JP-62241920, JP-1009225, and they were proposed as plastifiers, intermediates for the preparation of polyurethanes or for special applications, such as the preparation of substrates for optical disks. The polycarbonates of the invention, having intrinsic viscosities in chloroform at 30°C ranging from 0.05 dl/g to 2 dl/g, preferably from 0.077 to 0.32 dl/g, have biodegradability characteristics which make them useful for the preparation of bioerosible matrices. Therefore, the invention also relates to pharmaceutical compositions providing a slow release of the active principles from bioerosible matrices comprising polycarbonates of formula (I).

Polymers of formula I are prepared by reacting diols of formula (IV) or (V)

HO-R -OH HO-R -OH

(IV) (V) wherein R,1 and R 2 are as defined above, with 2 moles of l,l'-carbonyldiimidazole, to give diimidazolyl formates of formula (VI) or (VII)

(VI ) (VII ) which are in their turn reacted with diols of formula

( IV) or (V) . When R 1 and/or R2 are polyester residues, then the compounds (IV) and (V) are synthetized under - stream,

4 at 200°C, starting from a mixture containing HO-R -COOH and HO-R -COOH in the desired ratio and 1-10% w/w of

HO-R -OH and variable amounts of water.

The process is effected in aprotic solvents such as aliphatic or aromatic hydrocarbons, halogenated hydrocarbons, acetonitrile, dimethylsulfoxide, dimethylformamide, at a temperature from room temperature to the boiling temperature of the reaction mixture.

The following examples further illustrate the invention. EXAMPLE 1

4.97 g of l,l'-carbonyldiimidazole are added to an anhydrous solution of 3.05 g of polyethylene glycol 600 in 100 ml of "alcohol-free" chloroform. After 30 minutes the solution is stirred in the presence of 75 ml of water for 15 minutes; then it is extracted with

4x25 ml of water and dried over sodium sulfate. The

organic phase is filtered, solvent is evaporated off to obtain 3.82 g of diimidazolyl formate, 2.1249 g of which are mixed with 1.00 ml of a 1,6-hexanediol anhydrous solution in admixture with 1:1 "alcohol-free" σhloroform/dimethylsulfoxide having a concentration of 0.327 g/ml. After addition of 0.7538 g of imidazole and of a 1:1 chloroform/dimethylsulfoxide mixture to complete dissolution of the reagents, the solution is placed into a 60°C bath for four days, after that it is diluted to 150 ml with chloroform, extracted with 5x30 ml of water, dried over anhydrous sodium sulfate and filtered. By evaporation of the solvent, 1.56 g of polycarbonate are obtained, which is liquid at 20 ^β C and has an intrinsic viscosity of 0.25 dl/g, measured in chloroform at 30 ^β C by means of Ubbelohde viscosimeter.

EXAMPLE 2 The procedure of example 1 is followed, using triethylene glycol instead of polyethylene glycol 600. The amounts are as follows: 1.21 g of triethylene glycol

6.34 g of 1,1'-carbonyldiimidazole.

2.51 g of diimidazolyl formate are obtained, 2.2111 g of which are reacted with 3.67 ml of a 1,6- hexanediol anhydrous solution of concentration 0.215 g/ml and 1.7656 g of imidazole, to obtain 1.90 g of polycarbonate, which is liquid at 20 ^β C and has an intrinsic viscosity of 0.16 dl/g in chloroform at 30°C.

EXAMPLE 3 The procedure of example 1 is followed, replacing polyethylene glycol 600 with triethylene glycol and of the 1,6-hexanediol with 1,10-decanediol. The amounts

are as follows:

0.97 g of triethylene glycol

5.08 g of l,l'-carbonyldiimidazole.

2.01 g of diimidazolyl formate are obtained, 1.7395 g of which are reacted with 3.37 ml of a 1,10- decanediol solution of concentration 0.278 g/ml and 1.3988 g of imidazole. 1.83 g of polycarbonate are obtained, having melting point of 26-28"C and viscosity of 0.17 dl/g in chloroform at 30°C. EXAMPLE 4

The procedure of example 1 is followed, replacing polyethylene glycol 600 with triethylene glycol and 1,6-hexanediol with 1,12-dodecanediol. The amounts are as follows: 0.73 g of triethylene glycol

3.80 g of l,l'-carbonyldiimidazole.

1.51 g of diimidazolyl formate are obtained, 1.2493 g of which are reacted with 2.41 ml of a 1,12- dodecanediol solution of concentration 0.312 g/ml and 0.9845 g of imidazole. 1.49 g of polycarbonate are obtained, having melting point of 34-35°C and intrinsic viscosity of 0.19 dl/g in chloroform at 30 ^β C.

EXAMPLE 5 The procedure of example 1 is followed, using 2,2-dimethyl-l,3-propanediol instead of both polyethylene glycol 600 and 1,6-hexanediol. The amounts are as follows:

1.55 g of 2,2-dimeth l-l,3-propanediol 8.94 g of l,l'-carbonyldiimidazole. 4.06 g of diimidazolyl formate are obtained, 3.4482 g of which are reacted with 4.63 ml of a 2,2-

dimethyl-1,3-propanediol solution of concentration 0.259 g/ml and 2.8874 g of imidazole. 2.30 g of polycarbonate are obtained, having melting point of 70- 74 ^β C and intrinsic viscosity of 0.077 dl/g in chloroform at 30°C.

EXAMPLE 6 The procedure of example 1 is followed, replacing polyethylene glycol 600 with 2,2-dimethyl-l,3- propanediol and 1,6-hexanediol with 1,10-decanediol. The amounts are as follows:

1.62 g of 2,2-dimethyl-l,3-propanediol 9.37 g of l,l'-carbonyldiimidazole.

4.25 g of diimidazolyl formate are obtained, 3.5386 g of which are reacted with 8.80 ml of a 1,10- decanediol solution of concentration 0.243 g/ml and 3.1437 g of imidazole. 3.86 g of polycarbonate are obtained, which is liquid at 20°C, and has an intrinsic viscosity of 0.21 dl/g in chloroform at 30°C.

EXAMPLE 7 The procedure of example 1 is followed, using 1,10-decanediol instead of both polyethylene glycol 600 and 1,6-hexanediol. The amounts are as follows: 1.30 g of 1,10-decanediol 4.64 g of l,l'-carbonyldiimidazole. 2.43 g of diimidazolyl formate are obtained, 1.8584 g of which are reacted with 3.80 ml of a 1,10- decanediol solution of concentration 0.249 g/ml and 1.3768 g of imidazole. 2.06 g of polycarbonate are obtained, having melting point of 55-57°C and intrinsic viscosity of 0.19 dl/g in chloroform at 30°C.

EXAMPLE 8

The procedure of example 1 is followed, using 1,10-decanediol instead of polyethylene glycol 600 and 1,4-cyclohexanediol instead of 1,6-hexanediol. The amounts are as follows:

1.18 g of 1,10-decanediol

4.08 g of 1,1'-carbonyldiimidazole.

2.24 g of diimidazolyl formate are obtained, 1.7343 g of which are reacted with 2.45 ml of a 1,4- cyclohexanediol solution of concentration 0.229 g/ml and 1.4509 g of imidazole. 1.44 g of polycarbonate are obtained, having melting point of 91-100 ^β C and intrinsic viscosity of 0.15 del/g in chloroform at 30 ^β C. EXAMPLE 9

8.39 g of 1,1'-carbonyldiimidazole are dissolved in an anhydrous solution prepared from 1.42 g of 1,4- cyclohexanediol, 20 ml of dimethylsulfoxide and 100 ml of "alcohol-free" chloroform. The procedure of example 1 is followed, to obtain 3.50 g of diimidazolyl formate, 2.7414 g of which are reacted with 6.82 ml of a 1,10 decanediol solution of concentration 0.243 g/ml and 6.8294 g of imidazole. 3.12 g of polycarbonate are obtained having melting point of 88-93°C and intrinsic viscosity of 0.13 dl/g in chloroform at 30 ^β C.

EXAMPLE 10 The procedure of example 1 is followed, replacing 1,6-hexanediol with 1,10-decanediol. The amounts are as follows: 2.45 g of polyethylene glycol 600

2.78 g of diimidazolyl formate are obtained, 2.3646 g of which are reacted with 2.46 ml of a 1,10- decanediol solution of concentration 0.217 g/ml and 0.8538 g of imidazole. 2.19 g of polycarbonate are obtained, which is liquid at 20°C, having intrinsic viscosity of 0.28 dl/g in chloroform at 30°C.

EXAMPLE 11 The procedure of example 1 is followed, replacing 1,6-hexanediol with 2,2-dimethyl-l,3-propanediol. The amounts are as follows:

2.18 g of polyethylene glycol 600 2.23 g of 1,1'-carbonyldiimidazole.

2.47 g of diimidazolyl formate are obtained, 1.9386 g of which are reacted with 1.03 ml of a 2,2- dimethyl-l,3-propanediol solution of concentration 0.255 g/ml and 0.6935 g of imidazole. 1.74 g of polycarbonate are obtained, which is liquid at 20°C, having intrinsic viscosity of 0.21 dl/g in chloroform at 30 ^β C. EXAMPLE 12

The procedure of example 1 is followed, replacing 1,6-hexanediol with 1,4-cyclohexanediol. The amounts are as follows:

2.83 g of polyethylene glycol 600 3.16 g of 1,1'-carbonyldiimidazole.

3.24 g of diimidazolyl formate are obtained, 2.6828 g of which are reacted with 1.92 ml of a 1,4- cyclohexanediol solution of concentration 0.210 g/ml and 1.0459 g of imidazole. 2.39 g of polycarbonate are obtained, which is liquid at 20°C, having intrinsic viscosity of 0.26 dl/g in chloroform at 30 ^β C.

EXAMPLE 13

The procedure of example 1 is followed, replacing polyethylene glycol 600 with 2,2-dimethyl-l,3- propanediol. The amounts are as follows: 0.78 g of 2,2-dimethyl-l,3-propanediol 4.54 g of 1,1*-carbonyldiimidazole.

2.07 g of diimidazolyl formate are obtained, 1.4731 g of which are reacted with 2.67 ml of a 1,6- hexanediol solution of concentration 0.223 g/ml and 1.4725 g of imidazole. 1.32 g of polycarbonate are obtained, which is liquid at 20°C, having intrinsic viscosity of 0.17 dl/g in chloroform at 30°C.

EXAMPLE 14 The procedure of example 1 is followed, replacing polyethylene glycol 600 with 2,2-dimethyl-l,3- propanediol and 1,6-hexanediol with 1,12-dodecanediol. The amounts are as follows: 0.95 g of 2,2-dimethyl-l,3-propanediol 5.40 g of 1,1'-carbonyldiimidazole. 2.58 g of diimidazolyl formate are obtained, 1.8902 g of which are reacted with 5.66 ml of a 1,12- dodecanediol solution of concentration 0.231 g/ml and 1.5611 g of imidazole. 1.92 g of polycarbonate are obtained, which is liquid at 20 ^β C, having intrinsic viscosity of 0.19 dl/g in chloroform at 30 ^β C.

EXAMPLE 15 The procedure of example 1 is followed, using 1,6- hexanediol instead of polyethylene glycol 600. The amounts are as follows: 0.87 g of 1,6-hexanediol

4.99 g of 1,1'-carbonyldiimidazole.

2.08 g of diimidazolyl formate are obtained, 1.4806 g of which are reacted with 2.80 ml of a 1,6- hexanediol solution of concentration 0.204 g/ml and 1.5163 g of imidazole. 1.31 g of polycarbonate are obtained, having melting point of 58-60 ^β C and intrinsic viscosity of 0.18 dl/g in chloroform at 30°C.

EXAMPLE 16 The procedure of example 1 is followed, using 1,6- hexanediol instead of polyethylene glycol 600 and 1,10- decanediol instead of 1,6-hexanediol. The amounts are as follows:

1.04 g of 1,6-hexanediol 5.31 g of 1,1'-carbonyldiimidazole.

2.43 g of diimidazolyl formate are obtained, 1.7387 g of which are reacted with 4.10 ml of a 1,10- decanediol solution of concentration 0.241 g/ml and 1.7457 g of imidazole. 1.72 g of polycarbonate are obtained, having melting point of 40-44°C and intrinsic viscosity of 0.17 dl/g in chloroform at 30 ^β C. EXAMPLE 17

The procedure of example 1 is followed, using 1,10-decanediol instead of polyethylene glycol 600 and 1,12-dodecanediol instead of 1,6-hexanediol. The amounts are as follows: 1.04 g of 1,10-decanediol

3.56 g of 1,1'-carbonyldiimidazole.

2.05 g of diimidazolyl formate are obtained,

1.3943 g of which are reacted with 3.59 ml of a 1,12- dodecanediol solution of concentration 0.217 g/ml and 1.0176 g of imidazole. 1.41 g of polycarbonate are obtained, having melting point of 50-52°C and intrinsic

viscosity of 0.21 dl/g in chloroform at 30°C.

EXAMPLE 18 The procedure of example 1 is followed, using polyethylene glycol 1000 instead of polyethylene glycol 600. The amounts are as follows:

4.10 g of polyethylene glycol 1000 2.96 g of 1,1*-carbonyldiimidazole.

3.84 g of diimidazolyl formate are obtained, 2.8818 g of which are reacted with 1.25 ml of a 1,6- hexanediol solution of concentration 0.248 g/ml and 0.6723 g of imidazole. 2.46 g of polycarbonate are obtained, which is liquid at 20°C, having viscosity of 0.32 dl/g in chloroform at 30 ^β C.

EXAMPLE 19 The procedure of example 1 is followed, using 1,6- hexanediol instead of polyethylene glycol 600 and 1,4- cyclohexanediol instead of 1,6-hexanediol. The amounts are as follows: 1.04 g of 1,6-hexanediol 5.19 g of 1,1'-carbonyldiimidazole.

2.53 g of diimidazolyl formate are obtained, 1.6105 g of which are reacted with 2.83 ml of a 1,4- cyclohexanediol solution of concentration 0.216 g/ml and 1.7318 g of imidazole. 1.45 g of polycarbonate are obtained, having melting point of 110-115°C and intrinsic viscosity of 0.16 dl/g in chloroform at 30 ^β C.

EXAMPLE 20 The procedure of example 1 is followed, using 2,2- dimeth l-l,3-propanediol instead of polyethylene glycol 600 and 1,4-cyclohexanediol instead of 1,6-hexanediol. The amounts are as follows:

0.80 g of 2,2-dimethyl-l,3-propanediol 5.06 g of 1,1'-carbonyldiimidazole.

2.01 g of diimidazolyl formate are obtained, 1.4315 g of which are reacted with 2.74 ml of a 1,4- cyclohexanediol solution of concentration 0.208 g/ml and 1.4337 g of imidazole. 1.23 g of polycarbonate are obtained, having melting point of 142-148°C and intrinsic viscosity of 0.10 dl/g in chloroform at 30°C.

EXAMPLE 21 The procedure of example 1 is followed, replacing polyethylene glycol 600 with triethylene glycol and 1,6-hexanediol with 1,4-cyclohexanediol. The amounts are as follows: 1.31 g of triethylene glycol 5.97 of 1,1'-carbonyldiimidazole.

2.72 g of diimidazolyl formate are obtained, 1.9292 g of which are reacted with 3.25 ml of a 1,4- cyclohexanediol solution of concentration 0.204 g/ml and 1.3529 g of imidazole. 1.65 g of polycarbonate are obtained, having melting point of 31-34°C and intrinsic viscosity of 0.14 dl/g in chloroform at 30°C.

EXAMPLE 22 The procedure of example 1 is followed, replacing polyethylene glycol 600 with 2,5-dimethyl-2,5- hexanediol and 1,6-hexanediol with 1,10-decanediol. The amounts are as follows: 1.19 g of 2,5-dimethyl-2,5-hexanediol 4.33 g of 1,1'-carbonyldiimidazole.

2.54 g of diimidazolyl formate are obtained, 1.9980 g of which are reacted with 4.49 ml of a 1,10- decanediol solution of concentration 0.232 g/ml and

1.6272 g of imidazole. 1.98 g of polycarbonate are obtained, which is liquid at 20°C, having viscosity of 0.23 dl/g in chloroform at 30 ^β C.

EXAMPLE 23 The procedure of example 1 is followed, replacing polyethylene glycol 600 with 2,5-dimethyl-2,5- hexanediol and 1,6-hexanedio1 with triethylene glycol. The amounts are as follows: 1.12 g of 2,5-dimeth 1-2,5-hexanediol 4.87 g of 1,1'-carbonyldiimidazole.

2.38 g of diimidazolyl formate are obtained, 1.7605 g of which are reacted with 3.63 ml of a triethylene glycol solution of concentration 0.218 g/ml and 1.3938 g of imidazole. 1.67 g of polycarbonate are obtained, which is liquid at 20 ^β C, having viscosity of 0.16 dl/g in chloroform at 30 ^β C.

EXAMPLE 24 40.00 g of a 90% DL-lactic acid aqueous solution are reacted with 11.26 g of glycolic acid and 2.58 g of 1,10-decanediol at a temperature of 200 ^β C, with stirring, under nitrogen stream, for 24 hours. After that, the product is thoroughly dried and molecular weight is determined by osmometry (MW : 850). 2.52 g of the resulting oligo er are reacted with 1.11 g of 1,10- decanediol diimidazolyl formate (prepared as described in example 7) and 0.21 g of anhydrous imidazole in 5 ml of "alcohol-free" chloroform at a temperature of 60°C for 10 days. Then the mixture is diluted in 70 ml of chloroform, washed with 5x20 ml of water, dried over anhydrous sodium sulfate and filtered. Solvent is evaporated off, to obtain 2.08 g of polycarbonate,

which is solid at 25 ^β C, having intrinsic viscosity of 0.32 dl/g, measured with a ϋbbelhode viscosimeter in chloroform at 30 ^β C.

EXAMPLE 25 The procedure of example 24 is followed, using in the first step, for the preparation of the oligomer, DL-lactic acid, glycolic acid and ethylene glycol, instead of 1,10-decanediol. The amounts are as follows: 32.08 g of 90% DL-lactic acid aqueous solution 2.31 g of glycolic acid

3.35 g of ethylene glycol.

30.01 g of the oligomer are obtained, which is thoroughly dried. The molecular weight is determined by the osmometric method (MW : 700). The subsequent polymerization steps is also carried out as described in example 24, using the new oligomer of MW 700 instead of the one of MW 850, and 1,10-decanediol diimidazolyl formate. The amounts are as follows: 2.32 g of oligomer 0.98 g of 1,10-decanediol diimidazolyl formate 0.22 g of anhydrous imidazole.

2.51 g of polycarbonate are obtained, having intrinsic viscosity of 0.30 dl/g in chloroform at 30°C.

EXAMPLE 26 The procedure of example 24 is followed, using DL- lactic and glycolic acid in the following amounts: 18.51 g of 90% DL-lactic acid aqueous solution 14.41 g of glycolic acid 2 g of 1,10-decanediol. 31.81 g of oligomer are obtained, of MW: 650, determined by osmometry. 4,.51 g of said oligomer are

reacted with 1.99 g of 1,10-decanediol diimidazolyl formate (prepared as described in example 7) and 0.38 g of anhydrous imidazole; the polymer is recovered as in example 24. 4.38 g of polycarbonate are obtained, having intrinsic viscosity of 0.42 dl/g in chloroform at 30°C.

EXAMPLE 27 3.01 g of the oligomer prepared in example 24 (mw: 850) are reacted with 1.11 g of 1,1'- carbonyldiimidazole in 6 ml of "alcohol-free" chloroform at a temperature of 60 °C ; subsequently, 0.62 g of anhydrous 1,10-decanediol and 0.24 g of anhydrous imidazole are added to the reaction mixture, which is left to polymerize for 10 days at 60°C. Finally the product is purified, as described in example 24, to obtain 2.88 g of polycarbonate, having intrinsic viscosity of 0.32 dl/g in chloroform at 30 ^β C.

EXAMPLE 28 The procedure of example 27 is followed, using the oligomer prepared in example 24 (MW: 850). The amounts are as follows: 3.66 g of oligomer (MW: 850) 1.35 g of 1,1'-carbonyldiimidazole 5 ml of "alcohol-free" chloroform 0.75 g of 1,10-decanediol diimidazolyl formate

2.05 g of polycarbonate are obtained, having intrinsic viscosity of 0.45 dl/g in chloroform at 30 ^β C.

EXAMPLE 29 3.00 g of the oligomer prepared in example 24 (mw: 850) are reacted with 1.08 g of 1,4-cyclohexanediol diimidazolyl formate (prepared in example 9) and 0.31 g

of anhydrous imidazole at 60°C for 10 days. The procedure of example 24 is followed, to obtain 9.00 g of polycarbonate, having intrinsic viscosity of 0.30 dl/g in chloroform at 30 ^β C. EXAMPLE 30

2.25 g of the oligomer prepared in example 25 (MW: 700) are reacted with 1.02 g of 1,1'- carbonyldiimidazole in 5 ml of "alcohol-free" chloroform for 30 min. Then 2.25 g of the same oligomer MW 700 and 0.22 g of anhydrous imidazole are added to the reaction mixture, which is left to react for 10 days at 60°C. Finally the product is purified, as described in example 24, to obtain 4.80 g of polycarbonate, having intrinsic viscosity of 0.34 dl/g in chloroform at 30°C.

EXAMPLE 31 3.00 g of the oligomer prepared in example 25 (MW: 700) are reacted with 1.45 g of triethylene glycol diimidazolyl formate in 5 ml of "alcohol-free" chloroform and 0.30 g of anhydrous imidazole. Diimidazolyl formate is prepared as described in example 2, with the following amounts: 1.30 g of triethylene glycol 6.45 g of 1,1'-carbonyldiimidazole. The reaction mixture, which is left to react for 10 days at 60 "C. Finally the polymer is recovered as described in example 24, to obtain 2.98 g of polymer, having intrinsic viscosity of 0.35 dl/g in chloroform at 30 ^β C. EXAMPLE 32

A mixture consisting of 45 g of 1,12-

dodecanediol-polycarbonate (see Example 17) and 5 mg of deslorelin (Des-Gly ¹⁰ , D-Trp ⁶ , Proethy1amide ⁹ ) , a LHRH agonist peptide, was melted at 70°C to obtain a homogeneous mass, which, after cooling at 20°C, was milled and extruded from a piston equipped PTFE tube,

2 under a 100 kg/cm pressure and at 40 ^β C. The so obtained cylindric formulation (2 mm diamter, 10 mm length) was sterilized with gamma rays and subsequently used for therapeutic subcutaneous grafts.