Epoxide copolymerization

Besides olefin epoxidation, C02/epoxide copolymerization reactions were catalyzed with Zn-complex catalyst 10 (Figure 23) [91] as well as a silsesquinoxane-based Zn-complex [92] synthesized via multi-step in situ synthetic strategies. 

In contrast to the copolymerization of cyclic carbonates, the molecular weights are lower in the epoxide copolymerization 6,41 43). We assume that this is due to the presence of proton donors in the reaction mixture. They occur as impurities in epoxides 19,20) or anhydrides, moisture in all components of the copolymerization system, or their presence is a consequence of the high rate of hydrolysis of cyclic anhydrides 21). Proton donors added to the monomer feed remarkably decrease the molecular weight42 even in the copolymerization of ethylene glycol carbonate at 200 °C. Under these conditions, when recyclization of phthalic acid takes place 64) and the released C02 can tear off moisture to the gas phase, the molecular weight Mv decreases without proton donors from 45200 to 7100 in the presence of 5% phthalic acid or ethylene glycol or to 9300 in the presence of 15% water42,54. ... 

Table 2.25 Anhydride-epoxide copolymerization initiated by tertiary amines... 

Keywords Carbon dioxide and epoxides copolymerization Group 13 metal catalysts Group 3 metal catalysts Lactide polymerization Polycarbonate Polylactide... 

Fig. 18 Representative examples of homogeneous catalysts for CO epoxide copolymerization Inoue s tetraphenylporphyrin aluminium chloride complex (a), zinc hw-2,6-fluorophenoxide complex (b), zinc (3-diiminate complex (c) and chromium-salen complex (d)...

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. 

In contrast to the copolymerization of cyclic carbonates, the molecular weights are lower in the epoxide copolymerization We assume that this is due to... 

Kim BE, Varghese JK, Han YG, Lee BY (2010) Cobalt(lll) complexes of various salen-type ligand bearing four quaternary ammonium salts and their reaeTivity for C02/epoxide copolymerization. Bull Korenn Chem Setc 31 829-834... 

TMO Copolymerization With Saturated Epoxides. Copolymerizing TMO with ethylene oxide (EO) in an 80 20 weight ratio with the chelate catalyst gave a water-soluble product (90% of the total) which contained only 8% TMO (Run 2, Table II). On the basis of an ideal copolymerization, the EO is estimated to enter the copolymer in this fraction approximately 70 times more readily than does the TMO. This result confirms that alkylene oxides polymerize much more readily than oxetanes with the chelate catalyst. A small amount (10% of the Total) of a water-insoluble copolymer containing 44% TMO was obtained. This result indicates that the chelate catalyst contains some sites which give more favorable copolymerization. One possible explanation is that the unfavorable copolymerization of TMO at the major sites is due to steric hindrance which reduces the ability of TMO to coordinate at this site. 

In efforts to elucidate the mechanism of the original ZnEt2/H20 catalyst system, Inoue described the synthesis of polycarbonates from several optically active epoxides including styrene oxide (SO) (8,9), 3-phenyl-1,2-epoxypropane (10), cyclohexylepoxyethane (77) and 1,2-epoxybutane (EB) (P). The properties of the polycarbonates, however, are not discussed in these accounts. Other epoxides copolymerized by Inoue using the ZnEt2/H20 catalyst system include 1,2-, and 2,3-EB and isobutylene oxide (72) and glycidol ethers and carbonates (13). 

Yet, in related studies, mechanistic studies and theoretical calculations on (salen)AfX/nucleophile-mediated formation of cyclic carbonates from CO2 and PO, the authors proposed a bi-metaUic mechanism, involving a nucleophilic attack at an Al-coordinated epoxide species by an Al-bound nucleophile adduct [56]. Subsequent CO2 insertion into the newly formed Al-alkoxide bond, likely to be the rate-determining step of the all process, would then afford the corresponding Al-carboxylate derivative. Overall, further studies are certainly required for a complete understanding of the factors controlling and affecting Al-mediated CO2/ epoxide copolymerization reactions so that to allow the development of more active Al catalytic systems. 

Klaus, S. Lehenmeier, M.W. Herdtweck, E. Deghnaim, P Ott, A.K. Rieger, B. Mechanistic Insights into Heterogeneous Zinc Dicarboxylates and Theoretical Considerations for CO -Epoxide Copolymerization. J. Am. Chem. Soc. 2011, 133, 13151-13161. 

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