Copolymerization and Cycloaddition Products Derived from Coupling Reactions of 1,2-Epoxy-4-cyclohexene and Carbon Dioxide. Postpolymerization Functionalization via ThiolEne Click Reactions
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2014 American Chemical Society. The coupling reaction of 1,2-epoxy-4-cyclohexene with CO2 in the presence of a ZnCl2/nBu4NI catalyst system was shown to provide the naturally occurring cis-cyclohexadiene carbonate. An alternative synthesis of this compound, which was characterized by X-ray structural analysis, was carried out from the cis-diol and triphosgene. Upon utilizing binary or bifunctional (salen)CrX catalysts, this coupling process resulted in the selective formation of completely alternating copolymer of 1,2-epoxy-4-cyclohexene and carbon dioxide. In the case involving the binary chromium(III)/onium salt catalyst, small quantities of both the cis and trans cyclic carbonates were also produced. The (salen)CoDNP/PPNDNP (DNP = 2,4-dinitrophenolate) catalyst system was most effective at producing high molecular weight copolymer with 100% selectivity. The Tg of this polymer (Mn = 35.9 kDa) was determined to be 123 C, which is higher than the Tg (116 C) of the corresponding saturated copolymer. Depolymerization of poly(cyclohexadiene carbonate) to trans-cyclohexadiene carbonate occurred slowly and cleanly at 110 C following deprotonation of the terminal hydroxyl group. The trans-cyclohexadiene carbonate was independently synthesized via the carbonylation of the trans-diol with ethyl chloroformate. The hydrophobic 1,2-epoxy-4-cyclohexene/CO2 derived copolymer was modified by the quantitative addition of thioglycolic acid by way of the thiol-ene click reaction to afford an amphiphilic copolymer. Upon deprotonation of this functionalized polycarbonate with ammonium hydroxide, the production of a water-soluble polymeric material was achieved which displayed a Tg of 120 C.
author list (cited authors)
Darensbourg, D. J., Chung, W., Arp, C. J., Tsai, F., & Kyran, S. J.
complete list of authors
Darensbourg, Donald J||Chung, Wan-Chun||Arp, Christopher J||Tsai, Fu-Te||Kyran, Samuel J