Carbon dioxide copolymerization with epoxide

Copolymerization of carbon dioxide possibly also belongs to this class of polymerizations. Carbon dioxide copolymerizes with epoxides to polyanhydrides, with aziridines to polyurethanes, and with vinyl ethers to poly-ketoethers, i.e.. 

Some copolymerizations have been studied where one of the reactants is a compound not usually considered as a monomer. These include copolymerizations of epoxides and higher cyclic ethers with carbon dioxide, episulhdes with carbon dioxide and carbon disulhde, and epoxides with sulfur dioxide [Aida et al., 1986 Baran et al., 1984 Chisholm et al., 2002 Inoue and Aida, 1989 Soga et al., 1977]. The copolymers are reported to be either 1 1 alternating copolymers or contain 1 1 alternating sequences together with blocks of the cyclic monomer. 

A novel catalytic system based on aluminum porphyrins has been developed. It is particularly effective for the living ring-opening polymerization of epoxides and lactones and for the copolymerization of epoxides with carbon dioxide and with cyclic anhydrides. HNMR has demonstrated that the growing species of this initiating system is that shown in (3). 

Azelaic, sebacic, dodecanedioic, and brassyhc acids may be used in copolyetheresteramides (111). Two patents describe additional apphcations for the C-9—C-40 diacids for the preparation of polyester carbonates (112), and the copolymerization of epoxides and carbon dioxide by reaction of either glutaric or adipic acids with zinc oxide (113). 

An alternative method for generating enriched 1,2-diols from meso-epoxides consists of asymmetric copolymerization with carbon dioxide. Nozaki demonstrated that a zinc complex formed in situ from diethylzinc and diphenylprolinol catalyzed the copolymerization with cyclohexene oxide in high yield. Alkaline hydrolysis of the isotactic polymer then liberated the trans diol in 94% yield and 70% ee (Scheme 7.20) [40]. Coates later found that other zinc complexes such as 12 are also effective in forming isotactic polymers [41-42]. 

Equations 1 to 3 show some of fixation reactions of carbon dioxide. Equations la and lb present coupling reactions of CO2 with diene, triene, and alkyne affording lactone and similar molecules [2], in a process catalyzed by low valent transition metal compounds such as nickel(O) and palladium(O) complexes. Another interesting CO2 fixation reaction is copolymerization of CO2 and epoxide yielding polycarbonate (equation 2). This reaction is catalyzed by aluminum porphyrin and zinc diphenoxide [3],... 

Shi L, Lu X-B, Zhang R, Peng X-J, Zhang C-Q, Li J-E, Peng X-M (2006) Asymmetric alternating copolymerization and terpolymerization of epoxides with carbon dioxide at mild conditions. Macromolecules 39 5679-5685... 

Hsu T, Tan C (2002) Block copolymerization of carbon dioxide with cyclohexene oxide and 4-vinyl-1-cyclohexene-1,2-epoxide in based poly(propylene carbonate) by yttrium-metal... 

Switchable polarity solvents have recently been used in two chemical syntheses the polymerization of styrene (Figure 9.7) and carbon dioxide-epoxide copolymerization (Figure 9.8). In the first study,a non-stoichiometric mixture of DBU and 1-propanol was used as this gave a less viscous reaction mixture, which facilitated the filtration step and the isolation of the polystyrene. The recovered ionic liquid was turned back into the less polar mixture using nitrogen and could be reused four times with the addition of some makeup solvent to replace that lost in the filtration step. 

The high reactivity of these two classes of catalysts, carboxylate and alkoxide derivatives, has been confirmed by recent work of Coates and co-workers [87]. They reported the synthesis of two new types of Zn diimido complexes (30 and 31) as shown in Scheme 7 and successfully utilized both types of complexes in the copolymerization of CO2 with epoxides. Their high activities and selectivies in regard to the carbon dioxide insertion (up to 96% carbonate linkages) are unprecedented. 

Nakano, K. Kamada, T. Nozaki, K. Selective formation of polycarbonate over cyclic carbonate copolymerization of epoxides with carbon dioxide catalyzed by a cobalt(III) complex with a piperidinium end-capping arm. 

Carbon dioxide is an interesting synthetic feedstock, it can be copolymerized with heterocycles, such as epoxides, aziridines, and episulfides. In 1969, Inoue reported the zinc catalyzed sequential copolymerization of carbon dioxide and epoxides as a new route to polycarbonates (5,15). The reaction is shown in Figure 1.1. 

Supercritical carbon dioxide represents an inexpensive, environmentally benign alternative to conventional solvents for chemical synthesis. In this chapter, we delineate the range of reactions for which supercritical CO2 represents a potentially viable replacement solvent based on solubility considerations and describe the reactors and associated equipment used to explore catalytic and other synthetic reactions in this medium. Three examples of homogeneous catalytic reactions in supercritical CC are presented the copolymerization of CO2 with epoxides, ruthenium>mediated phase transfer oxidation of olefins in a supercritical COa/aqueous system, and the catalyic asymmetric hydrogenation of enamides. The first two classes of reactions proceed in supercritical CO2, but no improvement in reactivity over conventional solvents was observed. Hythogenation reactions, however, exhibit enantioselectivities superior to conventional solvents for several substrates. 

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