The present invention relates to a method for preparing a polycarbonate ether polyol, by reacting an epoxide and carbon dioxide in the presence of a catalyst of formula (I), a double metal cyanide (DMC) catalyst and a starter compound.

Background

Polyurethanes are polymers which are prepared by reacting a di- or polyisocyanate with a polyol. Polyurethanes are used in many different products and applications, including as insulation panels, high performance adhesives, high-resilience foam seating, seals and gaskets, wheels and tyres, synthetic fibres, and the like.

The polyols used to make polyurethanes are polymers which have multiple reactive sites (e.g. multiple hydroxyl functional groups). The polyols which are most commonly used are based on polyethers or polyesters.

One method for making polyether polyols in industry is by reacting an epoxide with a double metal cyanide (DMC) catalyst in the presence of a starter compound.

The nature and properties of the polyols have a great impact on the nature and the properties of the resultant polyurethanes. It is desirable to include polycarbonate linkages in the backbone of polyether polyols, as carbonate linkages in the polyol may improve the properties of the resultant polyurethane, for example, the presence of carbonate linkages may improve the UV stability, hydrolytic stability, chemical resistance and/or mechanical strength of the resulting polyurethane. The presence of carbonate linkages also increases the viscosity of the resulting polyol, which can limit use in some applications. It is therefore important to be able to control the ratio of ether linkages to carbonate linkages in polyols to tailor properties for widespread application. It is also important to be able to control the molecular weight and polydispersity of the polyol, as these properties impact usefulness and ease of processing of the resultant polyols.

DMC catalysts for use in the preparation of polyethers were first disclosed in US 3427256 by The General Tyre and Rubber Company. It was subsequently found that carrying out this reaction in the presence of a starter compound yielded a polyether polyol.

DMC catalysts are also capable of preparing polyether polyols which contain carbonate linkages in the polymer backbone (hereinafter referred to as polycarbonate ether polyols). To prepare these types of polymers, the reaction is typically carried out at high pressures of carbon dioxide. It has generally been found that, for DMC catalysts, in order to obtain appreciable incorporation of carbon dioxide, the reaction must be carried out at pressures of 40 bar or above. This is undesirable as industrial equipment for preparing polyols are typically limited to pressures of up to 10 bar. For example, in US 2013/0072602, the examples set out the polymerisation of propylene oxide in the presence of a starter compound, and an additive at 50 bar CO2. The resulting polycarbonate ether polyols incorporate between 17.8 and 24.1 wt% CO2. Similar results can be seen in US

2013/0190462.

In WO 2015/022290, the examples show that when the polymerisation of propylene oxide is carried out in the presence of a DMC catalyst and a starter compound in the range of 15-25 bar CO2, the resulting polyols incorporated between 10.0 and 15.4 wt% CO2.

It is therefore desirable to be able to prepare polycarbonate ether polyols under pressures used in industrial polyether polyol equipment. It is also desirable to obtain appreciable incorporation of carbon dioxide (e.g. >20 wt% carbon dioxide, which requires a proportion of carbonate linkages of -0.5 in the polymer backbone, depending on the nature of the starter used) under low pressures.

WO 2010/028362 discloses a method for making polycarbonate polyols by copolymerising carbon dioxide and an epoxide in the presence of a chain transfer agent and a catalyst having a permanent ligand set which complexes a single metal atom. The polyols prepared in the examples have a proportion of carbonate linkages≥0.95 in the polymer backbone. These systems are designed to prepare polycarbonates having little or no ether linkages in the polymer backbones. Furthermore, each of the examples is carried out at high pressures of 300 psig (about 20 bar) carbon dioxide.

WO 2013/034750 discloses a method for preparing polycarbonate polyols using a catalyst of formula (I):

The polyols prepared in the examples have≥95% carbonate linkages, and generally≥99% carbonate linkages in the polymer backbone.

WO 2012/121508 relates to a process for preparing polycarbonate ethers, which are ultimately intended for use as resins and soft plastics. This document is not concerned with preparing polyols. The process disclosed in WO 2012/121508 requires the copolymerisation of an epoxide and carbon dioxide in the presence of a DMC catalyst and a metal salen catalyst having the following formula:

The examples are each carried out at 16 bar CO2 or above. The resulting polycarbonate ethers contain varying amounts of ether and carbonate linkages. However, said polymers have a high molecular weight, have high polydispersity indices (that is, PDIs of 3.8 and above) and are not terminated by hydroxyl groups. These polymers cannot therefore be used to make

polyurethanes.

Gao et al, Journal of Polymer Science Part A: Polymer Chemistry, 2012, 50, 5177-5184, describes a method for preparing low molecular weight polycarbonate ether polyol using a DMC catalyst and a di-carboxylic acid starter. The proportion of carbonate linkages can be increased up to 0.75 in the resultant polyols by decreasing the temperature (50 °C) and increasing the pressure (40 bar), when using a dicarboxylic acid starter which is apparently crucial to the ability to prepare polyols with high proportions of carbonate linkages. These conditions are

unfavourable for economic industrial application. Gao et al suggests that dual catalysts systems for preparing polycarbonate ether polyols are unfavourable.

With previously reported catalyst systems, even at the widest range of temperature and pressures that have been deployed, it has reportedly not been possible to prepare polyols with proportions of carbonate linkages between 0.75 and 0.9.

Summary of the Invention

The invention relates to a method for preparing a polycarbonate ether polyol by reacting an epoxide and carbon dioxide in the presence of a catalyst of formula (I), a double metal cyanide (DMC) catalyst and a starter compound.

The catalyst of formula (I) is as follows:

M1 and M2 are independently selected from Zn(l l), Cr(l l), Co(l l), Cu(l l), Mn(l l), Mg(l l), Ni(l l), Fe(l l), Ti(l l), V(ll), Cr(l ll)-X, Co(l l l)-X, Mn(l l l)-X, Ni(l ll)-X, Fe(l ll)-X, Ca(l l), Ge(l l), Al(l ll)-X, Ti(l l l)- X, V(l I l)-X, Ge(l V)-(X)2 or Ti(l V)-(X)2;

F and R2 are independently selected from hydrogen, halide, a nitro group, a nitrile group, an imine, an amine, an ether group, a silyl group, a silyl ether group, a sulfoxide group, a sulfonyl group, a sulfinate group or an acetylide group or an optionally substituted alkyl, alkenyl, alkynyl, haloalkyl, aryl, heteroaryl, alkoxy, aryloxy, alkylthio, arylthio, alicyclic or heteroalicyclic group;

R3 is independently selected from optionally substituted alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene, arylene, heteroarylene or cycloalkylene, wherein alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene and heteroalkynylene, may optionally be interrupted by aryl, heteroaryl, alicyclic or heteroalicyclic;

R5 is independently selected from H, or optionally substituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, heteroaryl, alkylheteroaryl or alkylaryl;

E1 is C, E2 is O, S or NH or Ei is N and E2 is O;

E3, E4, E5 and E6 are selected from N, NR4, O and S, wherein when E3, E4, E5 or E6 are N, and wherein when E3, E4, E5 or E6 are NR4, O or

R4 is independently selected from H, or optionally substituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, heteroaryl, alkylheteroaryl, -alkylC(O)OR19 or -alkylC≡N or alkylaryl;

X is independently selected from OC(O)Rx, OSO2Rx, OSORx, OSO(Rx)2, S(O)Rx, ORx, phosphinate, halide, nitrate, hydroxyl, carbonate, amino, amido or optionally substituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl or heteroaryl;

Rx is independently hydrogen, or optionally substituted aliphatic, haloaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, alkylaryl or heteroaryl; and

G is absent or independently selected from a neutral or anionic donor ligand which is a Lewis base.

The DMC catalyst comprises at least two metal centres and cyanide ligands. The DMC catalyst may additionally comprise an organic complexing agent, water and/or a metal salt (e.g. in non-stoichiometric amounts).

For example, the DMC catalyst may comprise:

Wherein M' is selected from Zn(ll), Fe(ll), Ni(ll), Mn(ll), Co(ll), Sn(ll), Pb(ll), Fe(lll), Mo(IV), Mo(VI), Al(lll), V(V), V(VI), Sr(ll), W(IV), W(VI), Cu(ll), and Cr(lll),

M" is selected from Fe(ll), Fe(lll), Co(ll), Co(lll), Cr(ll), Cr(lll), Mn(ll), Mn(lll), Ir(lll), Ni(ll),

Rh(lll), Ru(ll), V(IV), and V(V); and

d, e, f and g are integers, and are chosen to such that the DMC catalyst has

electroneutrality.

The starter compound may be of the formula (III):

Z can be any group which can have 2 or more -Rz groups attached to it. Thus, Z may be selected from optionally substituted alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene, cycloalkylene, cycloalkenylene, hererocycloalkylene, heterocycloalkenylene, arylene, heteroarylene, or Z may be a combination of any of these groups, for example Z may be an alkylarylene, heteroalkylarylene,

heteroalkylheteroarylene or alkylheteroarylene group.

a is an integer which is at least 2, each Rz may be -OH, -NHR', -SH, -C(O)OH, -P(O)(OR")(OH), -PR'(O)(OH)2 or -PR'(O)OH, and R' may be H, or optionally substituted alkyl, heteroalkyl, aryl, heteroaryl, cycloalkyl or heterocycloalkyl.

The method can be carried out at pressure of between about 1 bar and about 60 bar, between about 1 bar and about 30 bar, between about 1 bar and about 20 bar, between about 1 bar and about 15 bar, or between about 1 bar and about 10 bar carbon dioxide. It will also be appreciated that the reaction is capable of being carried out at a pressure of about 5 bar or below.

The method can be carried out at temperatures of from about 0°C to about 250°C, for example from about 40°C to about 140°C, e.g. from about 50°C to about 1 10°C, such as from about 60°C to about 100°C, for example, from about 70°C to about 100°C.

The invention also provides a polymerisation system for the copolymerisation of carbon dioxide and an epoxide, comprising:

a. A catalyst of formula (I) as defined herein,

b. A DMC catalyst as defined herein, and

c. A starter compound as herein.

The invention is capable of preparing polycarbonate ether polyols which have n ether linkages and m carbonate linkages, wherein n and m are integers, and wherein m/(n+m) is from greater than zero to less than 1.

The polyols prepared by the method of the invention may be used for further reactions, for example to prepare a polyurethane, for example by reacting a polyol composition comprising a polyol prepared by the method of the invention with a composition comprising a di- or polyisocyanate.

Brief Description of Figures

Figure 1 is a GPC trace for Run 3 in Table 1 , showing the narrow polydispersity polyol produced by the combination of a catalyst of formula (I) and a DMC catalyst.

Figure 2 is a GPC trace for Run 2 in Table 1 , demonstrating the high polydispersity polyol produced by using a DMC catalyst alone.

Figure 3 is a GPC trace for Run 3 in Table 2, using 1 ,6-hexanediol as a starter.

Figure 4 is a GPC trace for Run 2 in Table 2, using PPG-725 as a starter.

Figure 5 is a GPC trace for Run 1 in Table 2, using PPG-1000 as a starter.

Figure 6 shows the viscosity at 75 °C of (approximately) Mw 2000 polyols prepared in Example 2, having varying CO2 content.

Figure 7 shows the viscosity at 25 °C of (approximately) Mw 2000 polyols prepared in Example 2, having varying CO2 content.

Figure 8 is a 1 H NMR spectrum of the polyol prepared in Example 2a, containing 33 wt% CO2.

Figure 9 is a 1 H NMR spectrum of the polyol prepared in Example 2b, containing 26.6 wt% CO2 and an RPEC of 0.67.

Figure 10 show the overlaid Thermogravimetrics Analysis (TGA) traces for examples 2a-e and Benchmark B2.

Definitions

For the purpose of the present invention, an aliphatic group is a hydrocarbon moiety that may be straight chain or branched and may be completely saturated, or contain one or more units of unsaturation, but which is not aromatic. The term "unsaturated" means a moiety that has one or more double and/or triple bonds. The term "aliphatic" is therefore intended to encompass alkyl, alkenyl or alkynyl groups, and combinations thereof. An aliphatic group is preferably a C1 -20 aliphatic group, that is, an aliphatic group with 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbon atoms. Preferably, an aliphatic group is a C1-15aliphatic, more preferably a C1-12aliphatic, more preferably a C1- 10aliphatic, even more preferably a C1 -8aliphatic, such as a C1-6aliphatic group.

An alkyl group is preferably a " C1 -20 alkyl group", that is an alkyl group that is a straight or branched chain with 1 to 20 carbons. The alkyl group therefore has 1 , 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 , 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbon atoms. Preferably, an alkyl group is a C1-15 alkyl, preferably a C1-12 alkyl, more preferably a C1-10 alkyl, even more preferably a C1- 8 alkyl, even more preferably a C1-6 alkyl group. Specifically, examples of " C1 -20 alkyl group" include methyl group, ethyl group, n-propyl group, iso-propyl group, n-butyl group, iso-

butyl group, sec-butyl group, tert-butyl group, n-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-eicosyl group, 1 , 1-dimethylpropyl group, 1 ,2-dimethylpropyl group, 2,2-dimethylpropyl group, 1 -ethyl propyl group, n-hexyl group, 1-ethyl-2-methylpropyl group, 1 , 1 ,2-trimethylpropyl group, 1 -ethylbutyl group, 1-methylbutyl group, 2-methylbutyl group, 1 , 1 -dimethylbutyl group, 1 ,2-dimethylbutyl group, 2,2-dimethylbutyl group, 1 ,3-dimethylbutyl group, 2,3-dimethylbutyl group, 2-ethylbutyl group, 2-methylpentyl group, 3-methylpentyl group and the like.

Alkenyl and alkynyl groups are preferably "C2-20alkenyl" and "C2-20alkynyl", more preferably "C2-1 5 alkenyl" and "C2-1 5 alkynyl", even more preferably "C2-12 alkenyl" and "C2-12 alkynyl", even more preferably "C2-1 0 alkenyl" and "C2-1 0 alkynyl", even more preferably "C2-8 alkenyl" and "C2-8 alkynyl", most preferably "C2-6 alkenyl" and "C2-6 alkynyl" groups, respectively.

A heteroaliphatic group (including heteroalkyl, heteroalkenyl and heteroalkynyl) is an aliphatic group as described above, which additionally contains one or more heteroatoms. Heteroaliphatic groups therefore preferably contain from 2 to 21 atoms, preferably from 2 to 16 atoms, more preferably from 2 to 13 atoms, more preferably from 2 to 11 atoms, more preferably from 2 to 9 atoms, even more preferably from 2 to 7 atoms, wherein at least one atom is a carbon atom. Particularly preferred heteroatoms are selected from O, S, N, P and Si. When heteroaliphatic groups have two or more heteroatoms, the heteroatoms may be the same or different.

Claims

1. A method for preparing a polycarbonate ether polyol, the method comprising reacting carbon dioxide and an epoxide in the presence of a double metal cyanide (DMC) catalyst, a catalyst of formula (I), and a starter compound,

wherein the catalyst of formula (I) has the following structure:

Wherein M1 and M2 are independently selected from Zn(ll), Cr(ll), Co(ll), Cu(l l), Mn(ll), Mg(ll), Ni(ll), Fe(ll), Ti(ll), V(ll), Cr(lll)-X, Co(lll)-X, Mn(lll)-X, Ni(lll)-X, Fe(lll)-X, Ca(ll), Ge(ll), Al(lll)-X, Ti(lll)-X, V(lll)-X, Ge(IV)-(X)2 or Ti(IV)-(X)2;

F and R2 are independently selected from hydrogen, halide, a nitro group, a nitrile group, an imine, an amine, an ether group, a silyl group, a silyl ether group, a sulfoxide group, a sulfonyl group, a sulfinate group or an acetylide group or an optionally substituted alkyl, alkenyl, alkynyl, haloalkyl, aryl, heteroaryl, alkoxy, aryloxy, alkylthio, arylthio, alicyclic or heteroalicyclic group;

R3 is independently selected from optionally substituted alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene, arylene, heteroarylene or cycloalkylene, wherein alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene and heteroalkynylene, may optionally be interrupted by aryl, heteroaryl, alicyclic or heteroalicyclic;

R5 is independently selected from H, or optionally substituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, heteroaryl, alkylheteroaryl or alkylaryl;

E1 is C, E2 is O, S or NH or Ei is N and E2 is O;

E3, E4, E5 and E6 are selected from N, NR4, O and S, wherein when E3, E4, E5 or E6 are and wherein when E3, E4, E5 or E6 are NR4, O or

R4 is independently selected from H, or optionally substituted aliphatic,

heteroaliphatic, alicyclic, heteroalicyclic, aryl, heteroaryl, alkylheteroaryl, - alkylC(O)OR19 or -alkylC≡N or alkylaryl;

X is independently selected from OC(O)Rx, OSO2Rx, OSORx, OSO(Rx)2, S(O)Rx, ORx, phosphinate, halide, nitrate, hydroxyl, carbonate, amino, amido or optionally substituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl or heteroaryl; Rx is independently hydrogen, or optionally substituted aliphatic, haloaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl, alkylaryl or heteroaryl; and

G is absent or independently selected from a neutral or anionic donor ligand which is a Lewis base; and

and wherein the starter is a compound having the following structure:

Z-( Rz)a (III)

Z is selected from optionally substituted alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene, cycloalkylene,

cycloalkenylene, hererocycloalkylene, heterocycloalkenylene, arylene,

heteroarylene, or Z may be a combination of any of these groups, such as an alkylarylene, heteroalkylarylene, heteroalkylheteroarylene or alkylheteroarylene group;

a is an integer which is at least 2; and

each Rz may be -OH, -NHR', -SH, -C(O)OH, PR'(O)(OH)2, -P(O)(OR')(OH) or - PR'(O)OH, preferably Rz may be -OH, -C(O)OH or -NHR', more preferably each Rz may be -OH, -C(O)OH or a combination thereof.

2. The method of claim 1 wherein the reaction is carried out at a pressure of between about 1 bar and about 60 bar carbon dioxide, preferably between about 1 bar and about 30 bar carbon dioxide, more preferably between about 1 bar and about 20 bar carbon dioxide, more preferably between about 1 bar and about 15 bar carbon dioxide, more preferably between about 1 bar and about 10 bar carbon dioxide.

3. The method of claim 1 or 2, wherein M an1 d/or M2 is selected from Mg(ll), Zn(ll), or Ni(ll), preferably wherein M1 and M2 are selected from Mg(ll), Zn(ll), or Ni(ll), .

4. The method of any preceding claim, wherein X is independently selected from

OC(O)Rx, OSO2Rx, OS(O)Rx, OSO(Rx)2, S(O)Rx, ORx, halide, nitrate, hydroxyl, carbonate, amino, nitro, amido, alkyl, heteroalkyl, aryl or heteroaryl, and/or Rx may be optionally substituted alkyl, alkenyl, alkynyl, heteroalkyl, aryl, heteroaryl, cycloalkyl, or alkylaryl.

5. The method of any preceding claim, wherein the catalyst of formula (I) has a symmetric macrocyclic ligand.

6. The method of any of claims 1 to 4, wherein the catalyst of formula (I) has an

asymmetric macrocyclic ligand.

7. The method of claim 6, wherein E3, E4, E5 and E6 are NR4, wherein at least one

occurrence of E3, E4, E5 and E6 is different to the remaining occurrence(s) of E3, E4, E5 and E6 are, preferably wherein R4 is H or alkyl.

8. The method according to any preceding claim, wherein the catalyst is of the formula:

9. The method according to any of claims 1 to 7, wherein the catalyst is of the formula:

10. The method of any preceding claim, wherein the reaction is carried out at a temperature in the range of from about 50°C to about 110°C, preferably from about 60°C to about 100°C.

11. The method of any preceding claim, wherein each occurrence of Rz may be -OH.

12. The method of any preceding claim, wherein a is an integer in the range of between about 2 and about 8, preferably in the range of about 2 and about 6.

13. The method of any of claims 1 to 10, wherein the starter compound is from diols such as 1 ,2-ethanediol (ethylene glycol), 1-2-propanediol, 1 ,3-propanediol (propylene glycol), 1 ,2-butanediol, 1-3-butanediol, 1 ,4-butanediol, 1 ,5-pentanediol, 1 ,6-hexanediol, 1 ,8- octanediol, 1 , 10-decanediol, 1 ,4-cyclohexanediol, 1 ,2-diphenol, 1 ,3-diphenol, 1 ,4- diphenol, neopentyl glycol, catechol, cyclohexenediol, 1 ,4-cyclohexanedimethanol, dipropylene glycol, diethylene glycol, tripropylene glycol, triethylene glycol, tetraethylene glycol, polypropylene glycols (PPGs) or polyethylene glycols (PEGs) having an Mn of up to about 1500g/mol, such as PPG 425, PPG 725, PPG 1000 and the like, triols such as glycerol, benzenetriol, 1 ,2,4-butanetriol, 1 ,2,6-hexanetriol, tris(methylalcohol)propane, tris(methylalcohol)ethane, tris(methylalcohol)nitropropane, trimethylol propane, polypropylene oxide triols and polyester triols, tetraols such as calix[4]arene, 2,2- bis(methylalcohol)-1 ,3-propanediol, erythritol, pentaerythritol or polyalkylene glycols (PEGs or PPGs) having 4-OH groups, polyols, such as sorbitol or polyalkylene glycols (PEGs or PPGs) having 5 or more -OH groups, diacids such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid,

suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid or other compounds having mixed functional groups such as lactic acid, glycolic acid, 3-hydroxypropanoic acid, 4-hydroxybutanoic acid, 5-hydroxypentanoic acid.

14. The method of any of claims 1 to 10, wherein the starter compound is a diol such as 1 ,2-ethanediol (ethylene glycol), 1-2-propanediol, 1 ,3-propanediol (propylene glycol), 1 ,2-butanediol, 1-3-butanediol, 1 ,4-butanediol, 1 ,5-pentanediol, 1 ,6- hexanediol, 1 ,8-octanediol, 1 , 10-decanediol, 1 , 12-dodecanediol, 1 ,4- cyclohexanediol, 1 ,2-diphenol, 1 ,3-diphenol, 1 ,4-diphenol, neopentyl glycol, catechol, cyclohexenediol, 1 ,4-cyclohexanedimethanol, poly(caprolactone) diol, dipropylene glycol, diethylene glycol, tripropylene glycol, triethylene glycol, tetraethylene glycol, polypropylene glycols (PPGs) or polyethylene glycols (PEGs) having an Mn of up to about 1500g/mol, such as PPG 425, PPG 725, PPG 1000 and the like, preferably wherein the starter compound is 1 ,6-hexanediol, 1 ,4- cyclohexanedimethanol, 1 ,12-dodecanediol, poly(caprolactone) diol, PPG 425,

PPG 725, or PPG 1000.

15. The method of any preceding claim, wherein the DMC catalyst is prepared by treating an aqueous solution of a metal salt with an aqueous solution of a metal cyanide salt in the presence of an organic complexing agent, preferably wherein the metal salt is of the formula M'(X')P, wherein M' is selected from Zn(ll), Fe(ll), Ni(ll), Mn(ll), Co(ll), Sn(ll), Pb(ll), Fe(lll), Mo(IV), Mo(VI), Al(lll), V(V), V(VI), Sr(ll), W(IV), W(VI), Cu(ll), and Cr(lll),

X' is an anion selected from halide, hydroxide, sulphate, carbonate, cyanide, oxalate, thiocyanate, isocyanate, isothiocyanate, carboxylate and nitrate, p is an integer of 1 or more, and the charge on the anion multiplied by p satisfies the valency of M';

the metal cyanide salt is of the formula (Y)qM"(CN) (A)c, wherein M" is selected from Fe(ll), Fe(lll), Co(ll), Co(lll), Cr(ll), Cr(lll), Mn(ll), Mn(lll), Ir(lll), Ni(ll), Rh(lll), Ru(ll), V(IV), and V(V),

Y is an alkali metal ion or an alkaline earth metal ion (such as K+),

A is an anion selected from halide, hydroxide, sulphate, cyanide oxalate, thiocyanate, isocyanate, isothiocyanate, carboxylate and nitrate;

q and b are integers of 1 or more;

c may be 0 or an integer of 1 or more;

the sum of the charges on the anions Y, CN and A multiplied by q, b and c respectively (e.g. Y x q + CN x b + A x c) satisfies the valency of M"; and

the complexing agent is an ether, a ketone, an ester, an amide, an alcohol, an urea or a combination thereof, preferably wherein the complexing agent is dimethoxyethane, tert-butyl alcohol, ethylene glycol monomethyl ether, diglyme, triglyme, ethanol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, or sec-butyl alcohol.

16. The method of any preceding claim, wherein the DMC catalyst comprises the formula:

Wherein M' and M" are as defined in claim 15, and d, e, f and g are integers, and are chosen to such that the DMC catalyst has electroneutrality,

preferably, d is 3, e is 1 , f is 6 and g is 2.

17. The method of claims 15 or 16 wherein M' is selected from Zn(ll), Fe(ll), Co(ll) and Ni(ll) and/or M" is selected from Co(ll), Co(lll), Fe(ll), Fe(lll), Cr(lll), Ir(lll) and Ni(ll), preferably M' is Zn(ll) and M" is Co(lll).

18. The method of claims 15 to 18, wherein the DMC catalyst additionally comprises water, an organic complexing agent and/or a metal salt.

19. A polymerisation system for the copolymerisation of carbon dioxide and an

epoxide, comprising:

a. A catalyst of formula (I) as defined in any preceding claim,

b. A DMC catalyst as defined in any preceding claim, and

c. A starter compound as defined in any preceding claim.

20. A polyol prepared by the method of any of claims 1 to 18.

21. A polyurethane or other higher polymer prepared from a polycarbonate ether polyol as defined in claim 20.