**5. Industrial activities and commercial advances**

A list of patents filed for the copolymerization of CO2 and epoxide is shown in Table 2. Since 1969, most patents filed for the copolymerization of CO2 and epoxides focused on developing heterogeneous catalysts, particularly zinc-based catalysts. The first catalyst, diethyl zinc, was developed by Inoue et al. in 1973 [89]. This patent that was sponsored by Nippon Oil Seal Industry Company demonstrated that the presence of co-catalyst significantly increased the yield of the copolymerization of ethylene oxide and CO2 nearly threefold. The co-catalyst includes a hydrogen donor-based compound that was added to an organometallic compound, formed from metals that belonged to group II or group III [90].

A process for preparing soluble zinc catalysts by the reaction of zinc compounds with either a dicarboxylic acid anhydride or an alcohol or a monoester of a dicarboxylic acid was reported and filed in 1987 [91]. This catalyst system that was soluble in most of solvents was useful for the copolymerization of epoxides and carbon dioxide to form polycarbonates. In 1989 and 1990, two patents, both sponsored by Japanese companies such as Mitsui Petrochemical Industries, were filed for the development of several catalysts containing zinc oxide that reacted with an organic dicarboxylic acid such as glutaric acid or adipic acid [92, 93]. These patents introduced zinc glutarate from the source of zinc oxide and glutaric acid as the most efficient catalyst for the copolymerization of propylene oxide and carbon dioxide.

In 1998, dicarboxylic acids were used to successfully synthesize co-, ter-, and block-polymers from epoxides and carbon dioxide. This study that was sponsored by Buna Sow Leuna Olefinverbund GmbH consisted of two dicarboxylic acids, which could be aliphatic, aromatic or a mixture of the two, in combination with a divalent inorganic zinc salt [94]. In 2003 and 2004, new patents were filed to investigate catalyst efficiency of a range of zinc complexes synthesized from different dicarboxylic acids (chosen from pentane diol, hexane diol, 1,5 dibromopentane, 1,5-dichloropentane, 1,6-dichlorohexane, 1,6-dibromohexane, glutaronitrile, adiponitrile, glutarimide, adipamide, glutaralaldehyde and adipaldehyde) precursor and zinc precursor (chosen from zinc acetate dihydrate, zinc hydroxide, zinc nitrate hexahydrate, zinc perchlorate hexahydrate, zinc oxide and zinc sulphate) [95, 96]. Among them, the complex synthesized of zinc perchlorate hexahydrate and glutaronitrile showed the highest yield of 67% over a period of 30-h reaction for copolymerization of PO and carbon dioxide.

As mentioned before, zinc carboxylates, particularly zinc glutarate, are the only group of catalysts that could be effective in the commercial and large-scale synthesis of polycarbonates. However, the activity of this group of catalysts is still remarkably lower than the conventional catalysts used for the synthesis of polyolefins. Consequently, many research and development activities are still focusing on novel catalysts for the synthesis of polycarbonates. For this purpose, most patents in the last decade focused on designing bimetallic or metal cyanide compounds to increase both yield and selectivity for the synthesis of polycarbonates [97]. For example, highly selective and active cobalt containing cyanide catalysts for producing poly(alkylene carbonates) from alkylene oxide and carbon dioxide was documented in 2005 [98]. However, the final product has still 10% cyclic carbonate by-product. In 2009, bimetallic complex of Zn(H), Co(II), Mn(II), Mg(II), Fe(II), Cr(III)-X or Fe(III)-X was reported for copoly‐ merization of carbon dioxide and cyclohexene oxide or propylene oxide [99]. Following these developments in 2012, a catalyst was invented from the reaction of one double-metal cyanide compound, one organic complexing agent and one primary alcohol having 6–24 carbon atoms (sponsored by Henkel Ag & Co.). The compound was effective in catalyzing both homopoly‐ merizations of epoxides or copolymerization of epoxides with carbon dioxide [100]. In the same year, a process for the synthesis of a polycarbonate from carbon dioxide and epoxides using a bimetallic catalyst system and a chain transfer agent was reported [101]. This invention that was sponsored by Imperial Innovations Limited exhibited that bimetallic complexes were successful in improvement of both activity and selectivity of PACs synthesis and accomplished above 90% yield of copolymerization with 99% carbonate linkage.

study, chromium salen catalyst, immobilized on the surface of silicates, was used for the copolymerization of styrene oxide and CO2 with nearly 50% activity and 80% selectivity [88]. In yet another example, aluminium salen catalyst, bonded on the surface of the polystyrene, was used for the copolymerization of CO2 and styrene oxide [87]. In addition to the potential of being recovered, the supported aluminium salen catalyst exhibited similar activity to the

A list of patents filed for the copolymerization of CO2 and epoxide is shown in Table 2. Since 1969, most patents filed for the copolymerization of CO2 and epoxides focused on developing heterogeneous catalysts, particularly zinc-based catalysts. The first catalyst, diethyl zinc, was developed by Inoue et al. in 1973 [89]. This patent that was sponsored by Nippon Oil Seal Industry Company demonstrated that the presence of co-catalyst significantly increased the yield of the copolymerization of ethylene oxide and CO2 nearly threefold. The co-catalyst includes a hydrogen donor-based compound that was added to an organometallic compound,

A process for preparing soluble zinc catalysts by the reaction of zinc compounds with either a dicarboxylic acid anhydride or an alcohol or a monoester of a dicarboxylic acid was reported and filed in 1987 [91]. This catalyst system that was soluble in most of solvents was useful for the copolymerization of epoxides and carbon dioxide to form polycarbonates. In 1989 and 1990, two patents, both sponsored by Japanese companies such as Mitsui Petrochemical Industries, were filed for the development of several catalysts containing zinc oxide that reacted with an organic dicarboxylic acid such as glutaric acid or adipic acid [92, 93]. These patents introduced zinc glutarate from the source of zinc oxide and glutaric acid as the most efficient catalyst for

In 1998, dicarboxylic acids were used to successfully synthesize co-, ter-, and block-polymers from epoxides and carbon dioxide. This study that was sponsored by Buna Sow Leuna Olefinverbund GmbH consisted of two dicarboxylic acids, which could be aliphatic, aromatic or a mixture of the two, in combination with a divalent inorganic zinc salt [94]. In 2003 and 2004, new patents were filed to investigate catalyst efficiency of a range of zinc complexes synthesized from different dicarboxylic acids (chosen from pentane diol, hexane diol, 1,5 dibromopentane, 1,5-dichloropentane, 1,6-dichlorohexane, 1,6-dibromohexane, glutaronitrile, adiponitrile, glutarimide, adipamide, glutaralaldehyde and adipaldehyde) precursor and zinc precursor (chosen from zinc acetate dihydrate, zinc hydroxide, zinc nitrate hexahydrate, zinc perchlorate hexahydrate, zinc oxide and zinc sulphate) [95, 96]. Among them, the complex synthesized of zinc perchlorate hexahydrate and glutaronitrile showed the highest yield of

67% over a period of 30-h reaction for copolymerization of PO and carbon dioxide.

As mentioned before, zinc carboxylates, particularly zinc glutarate, are the only group of catalysts that could be effective in the commercial and large-scale synthesis of polycarbonates. However, the activity of this group of catalysts is still remarkably lower than the conventional

unsupported aluminium salen compounds.

80 Advanced Catalytic Materials - Photocatalysis and Other Current Trends

**5. Industrial activities and commercial advances**

formed from metals that belonged to group II or group III [90].

the copolymerization of propylene oxide and carbon dioxide.




**Table 2.** List of the Filed Patents in the Field of CO2 and Epoxide Copolymerization
