Copolymerization and Cycloaddition Products Derived from Coupling Reactions of 1,2-Epoxy-4-cyclohexene and Carbon Dioxide. Postpolymerization Functionalization via Thiol–Ene Click Reactions

Abstract

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 T g of this polymer (M n = 35.9 kDa) was determined to be 123 °C, which is higher than the T g (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 T g of 120 °C.

Recent Advances in the Catalytic Preparation of Cyclic Organic Carbonates

“…The unsaturated epoxides have been employed with some success for the preparation of unsaturated polycarbonates which can easily undergo post-polymerization functionalization. 32,33 Moreover, the corresponding cyclic carbonate product, cis-cyclohexadiene carbonate is the simplest organic carbonate obtained from microbial/fungi methabolism.…”

Amphiphilic copolymers with pendent carboxyl groups for high-efficiency loading and controlled release of doxorubicin

“…mPEG-b-PATMC-g-SCH 2 COOH was synthesized by the thiol-ene "click" reaction [25][26][27]. 0.28 g (0.801 mmol allyl groups) of mPEGb-PATMC was dissolved in 3 ml of anhydrous tetrahydrofuran (THF) followed by adding 4.003 mmol (0.368 g) of thioglycolic acid and 4.003 mmol (0.657 g) of AIBN under a N 2 atmosphere.…”

Functional Polycarbonates from Carbon Dioxide and Tailored Epoxide Monomers: Degradable Materials and Their Application Potential

“…However, using an unsaturated derivative of CHO, Darensbourg et al were able to synthesize amphiphilic and water‐soluble polycarbonates. To obtain hydrophilic polycarbonates, the authors modified the side chains in a postpolymerization reaction with carboxyl groups via thiol‐ene click reaction, and in a second step with NH 4 OH to generate water‐soluble polyelectrolytes . Their work relied on the results of Honda et al and Winkler et al, who established the copolymerization of 1,4‐cyclohexadiene oxide and CO 2 to aliphatic polycarbonates in 2014.…”

“…Gu et al were able to enhance the hydrophilicity of PPC by terpolymerization, resulting in hydrophilic polycarbonates. Common CO 2 ‐based polycarbonates are hydrophobic, with the exception of polyions prepared by postpolymerization modification . Besides an increased hydrophilicity, also enhanced thermal stability was possible by the incorporation of bulky glycidyl ethers .…”