Copolymerization of carbon dioxide and ethyl vinyl ether at subcritical and supercritical conditions

Sustainable Copolymer Synthesis from Carbon Dioxide and Butadiene

Carbon dioxide (CO2) has long been recognized as an ideal C1 feedstock comonomer for producing sustainable materials because it is renewable, abundant, and cost-effective. However, activating CO2 presents a significant challenge because it is highly oxidized and stable. A CO2/butadiene-derived δ-valerolactone (EVP), generated via palladium-catalyzed telomerization between CO2 and butadiene, has emerged as an attractive intermediate for producing sustainable copolymers from CO2 and butadiene. Owing to the presence of two active carbon-carbon double bonds and a lactone unit, EVP serves as a versatile intermediate for creating sustainable copolymers with a CO2 content of up to 29 wt % (33 mol %). In this Review, advances in the synthesis of copolymers from CO2 and butadiene with divergent structures through various polymerization protocols have been summarized. Achievements made in homo- and copolymerization of EVP or its derivatives are comprehensively reviewed, while the postmodification of the obtained copolymers to access new polymers are also discussed. Meanwhile, potential applications of the obtained copolymers are also discussed. The literature references were sorted into sections based on polymerization strategies and mechanisms, facilitating readers in gaining a comprehensive view of the present chemistry landscape and inspiring innovative approaches to synthesizing novel CO2-derived copolymers.

Advances in the Synthesis of Copolymers from Carbon Dioxide, Dienes, and Olefins

ConspectusCarbon dioxide (CO₂) has long been considered a sustainable comonomer for polymer synthesis due to its abundance, easy availability, and low toxicity. Polymer synthesis from CO₂ is highly attractive and has received continuous interest from synthetic chemists. In this regard, alternating copolymerization of CO₂ and epoxides is one of the most well-established methods to synthesize aliphatic polycarbonates. Moreover, binucleophiles including diols, diamines, amino alcohols, and diynes have been reported to copolymerize with CO₂ to give polycarbonates, polyureas, polyurethanes, and polyesters, respectively. Nevertheless, little success has been made for incorporating CO₂ into the most widely used polyolefin materials.Although extensive studies have been focused on the copolymerization of olefins and CO₂, most of the attempted reactions resulted in olefin homopolymerization owing to the endothermic property and high energy barriers of CO₂ insertion during the chain propagation process. In this Account, we show how this challenge is addressed by taking advantage of a metastable lactone intermediate, 3-ethylidene-6-vinyltetrahydro-2H-pyran-2-one (EVP), which is produced from CO₂ and butadiene via palladium catalysis. Homopolymerization of EVP furnishes CO₂/butadiene copolymers with up to 29 wt % of CO₂ content. This reaction strategy represents a breakthrough for the long-standing challenge of inherent kinetic and thermodynamically unfavorable CO₂/olefin copolymerization. A new class of polymeric materials bearing repeating bicyclic lactone and unsaturated lactone units can be obtained. Importantly, one-pot copolymerization of CO₂/butadiene or terpolymerization of CO₂/butadiene/diene can be achieved to afford copolymers through a two-step reaction protocol. Interestingly, the bicyclic lactone units in the polymer chain can undergo ring-opening through hydrolysis and aminolysis, while reversible ring-closing of the hydrolyzed or aminolyzed units was also achieved simply by heating.Over the past few years, more and more studies have utilized EVP as an intermediate to synthesize copolymers from olefins, butadiene, and CO₂. Recently, we successfully incorporated CO₂ into the most widely used polyethylene materials via the direct copolymerization of EVP and ethylene. Taking advantage of the bifunctional reactivity of EVP, we were able to access two types of main-chain-functionalized polyethylenes through palladium-catalyzed coordination/insertion copolymerization and radical copolymerization. Besides polyethylenes, CO₂ was also incorporated into poly(methyl methacrylate), poly(methyl acrylate), polystyrene, polymethyl acrylate, polyvinylchloroacetate, and poly(vinyl acetate) materials via radical copolymerization of EVP and olefin monomers. The EVP/olefin copolymerization strategy provides a novel avenue for the synthesis of highly versatile copolymers from an olefin, CO₂, and butadiene.

Catalytic alcoholysis of urea to diethyl carbonate over calcined Mg–Zn–Al hydrotalcite

The synthesis of diethyl carbonate (DEC) from urea and ethanol was carried out over Mg–Zn–Al composite oxide catalysts derived from hydrotalcites (HTs).