PROCESS FOR THE PREPARATION OF POLYETHER POLYOLS

1 - 15 . (canceled)

16 . A process for the preparation of a polyethercarbonate polyol, comprising

(i) preparing, in a first step, a polyethercarbonate polyol chain from one or more H-functional starter substances, one or more alkylene oxides and carbon dioxide in the presence of at least one DMC catalyst, and

(ii) extending, in a second step, the polyethercarbonate polyol chain with a mixture of at least two different alkylene oxides in the presence of at least one DMC catalyst,

and in that the mixture of at least two different alkylene oxides in the second step (ii) is a mixture comprising propylene oxide (PO) and ethylene oxide (EO) in a molar ratio PO/EO of 15/85 to 60/40.

17 . The process according to claim 16 , wherein, in the first step (i),

(α) the H-functional starter substance or a mixture of at least two H-functional starter substances is taken and optionally water and/or other highly volatile compounds are removed by raising the temperature and/or reducing the pressure (“drying”), the DMC catalyst being added to the H-functional starter substance or the mixture of at least two H-functional starter substances before or after drying,

(β) for activation, a fraction, based on the total amount of alkylene oxides used in the activation and copolymerization, of one or more alkylene oxides is added to the mixture resulting from step (α), optionally, the alkylene oxide fraction is added in the presence of CO 2 , the hotspot that occurs due to the subsequent exothermic chemical reaction and/or a pressure drop in the reactor then being allowed to subside, and optionally, the activation step (β) is be carried out several times, and

(γ) one or more alkylene oxides and carbon dioxide are added to the mixture resulting from step (β), wherein the alkylene oxide in step (γ) is identical or different from the alkylene oxide used in step (β).

18 . The process according to claim 16 , wherein the mixture of at least two different alkylene oxides used in the second step (ii) is a mixture consisting of propylene oxide (PO) and ethylene oxide (EO) in a molar ratio PO/EO of 15/85 to 60/40.

19 . The process according to claim 16 , wherein, in the second step (ii), the molar ratio of propylene oxide (PO) to ethylene oxide (EO) is from 15/85 to 40/60.

20 . The process according to claim 16 , further comprising

(iii) extending the polyethercarbonate polyol chain with terminal mixed block, resulting from step (ii), with an alkylene oxide.

21 . A polyethercarbonate polyol comprising a terminal mixed block of at least two alkylene oxides, wherein the terminal mixed block comprises a mixture of propylene oxide (PO) and ethylene oxide (EO) in a molar ratio PO/EO of 15/85 to 60/40.

22 . The polyethercarbonate polyol according to claim 21 , wherein the terminal mixed block consists of a mixture of propylene oxide (PO) and ethylene oxide (EO) in a molar ratio PO/EO of 15/85 to 60/40.

23 . The polyethercarbonate polyol according to claim 21 , wherein the molar ratio of propylene oxide (PO) to ethylene oxide (EO) in the mixed block is from 15/85 to 40/60.

24 . The polyethercarbonate polyol according to claim 21 , wherein the chain of the terminal mixed block is extended with an alkylene oxide.

25 . The polyethercarbonate polyol according to claim 21 , wherein the mean length of the terminal mixed block of at least two different alkylene oxides is from 2.0 to 20.0 alkylene oxide units.

26 . A process for the production of a flexible polyurethane foam comprising utilizing a polyol comprising the polyethercarbonate polyol according to claim 21 as component A.

27 . The process for the production of a flexible polyurethane foam with a gross density according to DIN EN ISO 3386-1-98 in the range from ≧10 kg/m3 to ≦150 kg/m3 and a compressive strength according to DIN EN ISO 3386-1-98 in the range from ≧0.5 kPa to ≦20 kPa, at 40% deformation after 4th cycle, by reacting component A comprising

A1 100 to 10 parts by weight, based on the sum of the parts by weight of components A 1 and A2, of polyethercarbonate polyol according to claims 21 ,

A2 0 to 90 parts by weight, based on the sum of the parts by weight of components A1 and A2, of conventional polyether polyol,

A3 0.5 to 25 parts by weight, based on the sum of the parts by weight of components A1 and A2, of water and/or physical blowing agents,

A4 0.05 to 10 parts by weight, based on the sum of the parts by weight of components A1 and A2, of an auxiliary substance and/or an additive, and

A5 0 to 10 parts by weight, based on the sum of the parts by weight of components A1 and A2, of compounds having isocyanate-reactive hydrogen atoms with a molecular weight of 62-399,

with component B comprising a polyisocyanate,

the preparation taking place at an index of 50 to 250, and all the parts by weight of components A1 to A5 in the present patent application being scaled so that the sum of the parts by weight of components A1+A2 in the composition is 100.

28 . The process according to claim 27 wherein component A consists of

A1 100 parts by weight of polyethercarbonate polyol according to claim 21 ,

A2 0 parts by weight of conventional polyether polyol,

A3 0.5 to 25 parts by weight (based on the parts by weight of component A1) of water and/or physical blowing agents,

A4 0.05 to 10 parts by weight (based on the parts by weight of component A1) of an auxiliary substances and/or an additive, and

A5 0 to 10 parts by weight (based on the parts by weight of component A1) of compounds having isocyanate-reactive hydrogen atoms with a molecular weight of 62-399.

29 . The process for the production of a flexible polyurethane foam comprising utilizing a polyol component (component A) which comprises a polyethercarbonate polyol obtained according to claim 16 .

30 . A flexible polyurethane foam with a gross density according to DIN EN ISO 3386-1-98 in the range from ≧10 kg/m 3 to ≦150 kg/m 3 and a compressive strength according to DIN EN ISO 3386-1-98 in the range from ≧0.5 kPa to ≦20 kPa, at 40% deformation after 4 th cycle, obtained by the process according to claim 26 .