Method for producing polycarbonate polyols by the immortal polymerization of cyclic carbonates

1. A process for preparing a polycarbonate polyol, comprising polymerizing cyclic carbonate in the presence of DMC catalyst and chain-transfer agent, wherein the chain-transfer agent consists of polyether carbonate polyol and is prepared beforehand in a separate reaction step.

2. The process according to claim 1 , wherein the cyclic carbonate is at least one compound selected from the group consisting of compounds of formulae (I) and (II)

wherein

R1, R4 and R5 independently of one another represent hydrogen or a linear or branched C1 to C12 alkyl radical or a C6 to C10 aryl radical, and

R2 and R3 independently of one another represent hydrogen or a linear or branched C1 to C12 alkyl radical or a C6 to C10 aryl radical or an allyloxymethyl radical.

3. The process according to claim 1 , wherein the cyclic carbonate is at least one selected from the group consisting of trimethylene carbonate, neopentyl glycol carbonate, 2,2,4-trimethyl-1,3-pentanediol carbonate, 2,2-dimethyl-1,3-butanediol carbonate, 1,3-butanediol carbonate, 2-methyl-1,3-propanediol carbonate, 2,4-pentanediol carbonate, 2-methyl-butane-1,3-diol carbonate, TMP-monoallyl ether carbonate, pentaerythritol diallyl ether carbonate, propylene carbonate, phenylethylene carbonate and ethylene carbonate.

4. The process according to claim 1 , wherein the DMC catalyst comprises zinc hexacyanocobaltate(III) which comprises as organic complex ligands tert-butanol and a polyether polyol having a number-average molecular weight of at least 500 g/mol.

5. The process according to claim 1 , wherein trimethylene carbonate is used as the cyclic carbonate.

6. The process according to claim 1 , wherein polymerisation of the cyclic carbonate takes place in the presence of DMC catalyst and at least one chain-transfer agent at a reaction temperature of from 60 to 160° C.

7. The process according to claim 1 , wherein the weight ratio of chain-transfer agent to cyclic carbonate is from 1:0.001 to 1:50.

8. The process according to claim 1 , wherein

(i) H-functional starter substance, or a mixture of at least two H-functional starter substances, is placed in a reaction vessel, and water and/or other readily volatile compounds are optionally removed by drying, wherein the DMC catalyst, the H-functional starter substance, or the mixture of at least two H-functional starter substances, are added before and/or after the drying,

(ii) an alkylene oxide and carbon dioxide are added to the mixture resulting from (i) thereby comprising copolymerisation with formation of the polyether carbonate polyol chain-transfer agent,

(iii) to the mixture resulting from (ii), there is added a cyclic carbonate, which can be the same as or different from the cyclic carbonate contained in the mixture resulting from (ii), wherein the weight ratio of mixture resulting from (ii) to added cyclic carbonate is from 1:0.001 to 1:50, and a resulting mixture is reacted at a temperature of from 60 to 160° C.

9. The process according to claim 8 , wherein no DMC catalyst is added in (iii).

10. The process according to claim 1 , wherein there is used as the chain-transfer agent a polycarbonate which has been prepared by said process.

11. An aliphatic polycarbonate obtainable by a process according to claim 1 .

12. The process according to claim 1 , wherein the polycarbonate polyol has a content of primary OH groups of at least 80%.

13. The process according to claim 1 , wherein the chain-transfer agent consists of a mixture of different polyether carbonate polyols.

14. The process according to claim 1 , further comprising reacting the polycarbonate polyol with a diisocyanate and/or polyisocyanate to form a polyurethane.