Epoxides alternating copolymerization

The synthesis of polycarbonates from the alternating copolymerization of epoxides with C02 was first reported in 1969 using a ZnEt2/H20 mixture.954 Subsequent studies have focused upon a... 

Abstract Development in the field of transition metal-catalyzed carbonylation of epoxides is reviewed. The reaction is an efficient method to synthesize a wide range of / -hydroxy carbonyl compounds such as small synthetic synthons and polymeric materials. The reaction modes featured in this chapter are ring-expansion carbonylation, alternating copolymerization, formylation, alkoxycarbonylation, and aminocarbonylation. 

It is also possible to desymmetiize a meso epoxide in the alternating copolymerization. Thus, asymmetric alternating copolymerization of cyclohexene oxide with CO2 catalyzed by a dimeric zinc complex provides a polycarbonate in which the diol unit is optically active with 80% ee. (See Scheme 4.24.)... 

Lu X-B, Wang Y (2004) Highly active, binary catalyst systems for the alternating copolymerization of CO2 and epoxides under mild conditions. Angew Chem Int Ed 43 3574—3577... 

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... 

Fig. 16 Proposed mechanism for the epoxide/CO alternating copolymerization, including pyridine mediation...

Coates and coworkers have carried out kinetic studies of the alternating copolymerization of CHO and C02 catalyzed by several of the P-diiminate zinc derivatives [29]. These authors have proposed a bimetallic mechanism to be operative, which is consistent with their experimental observations, including the large differences in activity noted for a series of structurally closely related catalysts. It was proposed that one zinc center would coordinate and activate the epoxide substrate, while the second zinc center would provide the propagating carbonate species to ring-open the epoxide. This proposal is represented by the transition state depicted in Figure 8.3a. 

Figure 3.10. Highly active Zn(II)-based catalysts for the alternating copolymerization of C02 and epoxides. R = CH(CH3)2.

Carbon dioxide is an attractive renewable resource being of low toxicity, abundant and the waste product of many processes. There is precedent, dating back to 1969, for the copolymerization of C02 and strained heterocycles, most notably epoxides [18]. The focus on this review will be on understanding the polymerization catalysts for the alternating copolymerization. 

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. 

Table I. Alternating Copolymerization of Epoxide and Phthallc Anhydride with TPPAlCl-EtPhsPBr System...

If well defined spacer segments are desired, the synthesis of polysoaps becomes more complicated. Homopolymerization of other than vinylic surfactant monomers, e.g. of epoxides [312], butadienes [168, 313] or vinylcyclo-propanes [168] is needed (for examples see Tables 2 and 4). Alternatively, strictly alternating copolymerization enables the preparation of defined repeat units longer than C2-fragments [54, 82, 168-170, 184-187, 189-192, 195-197,... 

It is interesting that unsaturated polyesters can actually be prepared by anionic alternating copolymerization of an epoxide and bicyclic bis(y-butyrolactone) bearing an isopropenyl group [34]. The reaction was illustrated as follows ... 

Darensbourg, D.J., Fitch, S.B., 2007. (Tetramethyl tetraaza annulene)chromium chloride a highly active catalyst for the alternating copolymerization of epoxides and carbon dioxide. Inorganic Chemistry 46, 5474—5476. 

We have found for the first time the alternating copolymerization of carbon dioxide and epoxide catalyzed by some organometallic systems to give an aliphatic polycarbonate of high molecular weight. 

Moore, D. R. Cheng, M. Lohkovsky, E. B. Coates, G. W. Mechanism of the alternating copolymerization of epoxides and CO2 using beta-diiminate zinc catalysts Evidence for a bimetallic epoxide enchainment. J. Am. Chem. Soc. 2003,125, 11911-11924. 

Cheng M, Moore DR, Reczek JJ, Chamberlain BM, Lobkovsky BE, Coates GW (2001) Single-site p-diiminate zinc catalysts for the alternating copolymerization of CO2 and epoxides catalyst synthesis and unprecedented polymerization activity. J Am Chem Soc 123 8738-8749... 

Carbon Dioxide as a Renewable Cl Feedstock Synthesis and Characterization of Polycarbonates from the Alternating Copolymerization of Epoxides and CO2... 

Given the high activity and selectivity of catalyst 4 and the variety of commercially available epoxides, we explored the versatility of 4 as a catalyst for the alternating copolymerization of other aliphatic epoxides. The copolymerizations of aliphatic epoxides with saturated and unsaturated hydrocarbon chains were examined flrst, and the results are shown in Table I. 

The alternating copolymerization of cis/fraws-limonene oxide and carbon dioxide can be achieved with p-diiminate zinc acetate complexes (Scheme 5). The balance between high catalyst activity and selectivity is optimal with catalyst complex 8 (see Scheme 5, right) at 25°C. Catalysts exhibits high selectivity for the trans diasteriomer (% trans in the copolymer is >98%). The biodegradable polycarbonates have MWs in the range of 4.0-10.8 kg/mol, which can be controlled by the [epoxide]/[Zn] ratio, CO2 pressure, and reaction time. They also have narrow... 

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