Synthesis and application of CO₂-based polycarbonate polyols and their polyurethanes

The copolymerization of carbon dioxide and epoxides is utilized to synthesize carbon dioxide-based polycarbonate polyols, which are used to prepare carbon dioxide-based polyurethane materials. This approach is becoming an integral part of green polymer chemistry. It is also at the forefront of the national carbon neutrality strategy. This review primarily focuses on the synthesis methods of carbon dioxide-based polycarbonate polyols in recent years. Emphasis is placed on the research progress of immortal polymerization of carbon dioxide and epoxides in the presence of chain transfer agents, which is further classified and reviewed based on heterogeneous catalysts, homogeneous metal catalysts, and homogeneous non-metallic catalysts. Furthermore, the extensive applications of carbon dioxide-based polyols in environmentally friendly polyurethanes and other fields are discussed, and the future development trends are predicted. Carbon dioxide-based (CO2-based) copolymers as environmentally friendly materials are highly promising due to their excellent biodegradability. These copolymers effectively utilize carbon dioxide gas, which is abundant, non-toxic, and cost-effective, as one of their raw materials. Given that CO2 is emitted as a waste gas in numerous economic activities, leading to global warming, the chemical fixation of CO2 presents a compelling and effective approach to alleviating environmental and energy pressures. The direct utilization of CO2 in the production of degradable low molecular weight polycarbonate polyols or oligo(carbonate-ether) polyols via epoxides/CO2 copolymerization has attracted much attention to both academic researches and industrial productions over the past decades due to the following advantages: First, there is no toxic phosgene generated, so it is totally eco-friendly; second, CO2 is one of the main and renewable materials to reduce dependence on petroleum resources; third, CO2 as feedstocks is abundant, and inexpensive, which cuts down the cost of produced polyurethane (PU). Regarding the current research situation, the main issues in the copolymerization reaction of carbon dioxide and epoxides are low catalytic efficiency, high catalyst cost, harsh reaction conditions, low copolymer yield, and complex catalyst separation. We have summarized the new catalytic system of copolymers of carbon dioxide and epoxides, and discussed the advantages and disadvantages of various catalytic systems including dimetallic cyanide catalysts, metallic Salen catalysts, metalloporphyrin catalysts and new organic catalysts, which have important application values for the resource utilization of carbon dioxide. Metal-containing catalysts are the earliest catalytic systems used for the synthesis of high molecular polycarbonate from CO2, and hence are also firstly employed for the synthesis of poly (propylene carbonate) diols from CO2 and epoxides. The copolymerization of carbon dioxide and epoxides is utilized to synthesize poly(propylene carbonate) diols, which are used to prepare carbon dioxide-based polyurethane materials. Polyurethane is an indispensable polymeric material in our daily lives. PUs prepared by poly(propylene carbonate) diols, which are called as poly(carbonate urethane)s (PCUs) possess many advantages such as excellent mechanical properties, hydrolysis resistance, abrasive resistance, oil and chemical resistance and excellent biocompatibility compared with normal polyurethanes synthesized from the conventional polyether and polyester diols. Therefore, the synthesis of poly (propylene carbonate) diols as feedstocks for poly(carbonate urethane)s has attracted more and more attention in recent years. Furthermore, the extensive applications of carbon dioxide-based polyols in environmentally friendly polyurethanes and other fields are discussed, and the future development trends are predicted.