Epoxide copolymerization reaction

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. 

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. 

Cr(III) and Co(III) complexes of these ligand sets have led to extremely significant new findings in the area of epoxide/C02 copolymerization reactions (vide infra). 

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. ... 

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. 

C02, or from epoxide and cyclic acid anhydride. Because preliminary studies indicated that trlphenylphosphlne was converted to a quaternary salt in the reaction, the effect of a quaternary phosphonlum or eumnonlum salt separately prepared was examined. As a result of this investigation, the system containing an aluminum porphyrin and phosphonlum or ammonium salt was found to be a novel, effective catalyst for these alternating copolymerization reactions and to yield products with narrow molecular weight distribution. 

Some of the major copolymerization reactions of isocyanates are shown in Scheme 2. Only the reaction with epoxides is discussed in this chapter. The reaction with polyols to give polyurethanes and with amines to give polyureas is discussed in Vol. I of this series [2]. Ulrich [2a] has briefly reviewed these and other reactions and this review should be consulted for additional material and references. 

Darensbourg DJ, Yarbrough JC (2002) Mechanistic aspects of the copolymerization reaction of carbon dioxide and epoxides, using a chiral salen chromium chloride catalyst. J Am Chem Soc 124 6335-6342... 

It is clear from the numerous accounts in literature that DMCs can efficiently catalyze the copolymerization of CO2 and epoxides. DMCs can however also be used to develop systems that selectively catalyze the CO2 cycloaddition rather than the copolymerization (Scheme 1.4) as is illustrated by the work of Dharman et al. [20]. By itself, a Zn-Co-DMC is an efficient catalyst for the copolymerization reaction. However, the addition of a quaternary ammonium salt to the reaction mixture switches the selectivity of the catalytic system toward the exclusive formation of the cyclic carbonate. The quaternary ammonium ion plays two important roles in the catalytic system it accelerates the diffusion of CO2 into the reaction mixture and it favors a backbiting mechanism. As such, it hinders the growth of the polymer chain and it enables the selective cyclic carbonate production. Although most zinc-containing catalysts for this reaction are very sensitive toward water, Wei et al. have shown that, for example, the combination of Zn-Co-DMC with CTAB (cetyltrimethylammonium bromide) could even use water-contaminated epoxides as an epoxide feed [21]. 

Darensbourg, D. J. Yarbrough, J. C. Mechanistic Aspects of the Copolymerization Reaction of Carbon Dioxide and Epoxides, Using a Chiral Salen Chromium Chloride Catalyst. J. Am. Chem. Soc. 2002,124, 6335-6342. 

Although acetonitrile is one of the more stable nitriles, it undergoes typical nitrile reactions and is used to produce many types of nitrogen-containing compounds, eg, amides (15), amines (16,17) higher molecular weight mono- and dinitriles (18,19) halogenated nitriles (20) ketones (21) isocyanates (22) heterocycles, eg, pyridines (23), and imidazolines (24). It can be trimerized to. f-trimethyltriazine (25) and has been telomerized with ethylene (26) and copolymerized with a-epoxides (27). 

The reaction of OF2 and various unsaturated fluorocarbons has been examined (35,36) and it is claimed that OF2 can be used to chain-extend fluoropolyenes, convert functional perfluorovinyl groups to acyl fluorides and/or epoxide groups, and act as a monomer for an addition-type copolymerization with diolefins. 

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). 

Extensive studies of stereoselective polymerization of epoxides were carried out by Tsuruta et al.21 s. Copolymerization of a racemic mixture of propylene oxide with a diethylzinc-methanol catalyst yielded a crystalline polymer, which was resolved into optically active polymers216 217. Asymmetric selective polymerization of d-propylene oxide from a racemic mixture occurs with asymmetric catalysts such as diethyzinc- (+) bomeol218. This reaction is explained by the asymmetric adsorption of monomers onto the enantiomorphic catalyst site219. Furukawa220 compared the selectivities of asymmetric catalysts composed of diethylzinc amino acid combinations and attributed the selectivity to the bulkiness of the substituents in the amino acid. With propylene sulfide, excellent asymmetric selective polymerization was observed with a catalyst consisting of diethylzinc and a tertiary-butyl substituted a-glycol221,222. ... 

Based on the above results and previous works [3,9] on the reaction of epoxides and CO2, we tentatively propose the plausible mechanism for the copolymerization of GMA and CO2 (schane 1), Alkyhnethyl imidazolim salt (QX) and epoxide (GMA) r cted to synthesize an active spedes followed by chain propagation involving a < ncerted insertion of th e epoxide. However, more detailed mechanistic studies are needed to clairly understand the polymerization steps. 

The trigonal planar zinc phenoxide complex [K(THF)6][Zn(0-2,6-tBu2C6H3)3] is formed by the reaction of a zinc amide complex, via a bis phenoxide, which is then further reacted with potassium phenoxide. TheoX-ray structure shows a nearly perfect planar arrangement of the three ligands with zinc only 0.04 A out of the least squares plane defined by the three oxygen atoms.15 Unlike the bisphenoxide complexes of zinc with coordinated THF molecules, these complexes are not cataly-tically active in the copolymerization of epoxides with C02. The bisphenoxide complex has also been structurally characterized and shown to be an effective polymerization catalyst. 43... 

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],... 

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