CO2-Based Block Copolymers: Present and Future Designs

Polycarbonates derived in part from carbon dioxide are provided by the completely alternating incorporation of epoxide and CO2 molecules into a growing polymer chain. This process is an alternative to the step-growth, environmentally unfavorable pathway involving diols and phosgene. A major challenge in synthesizing block polymers is the ability to chemoselectively control the incorporation of monomers from the polymerization of a mixed monomer feedstock. This ability to direct the polymer sequences of course determines the polymer structure and thermal/mechanical properties. Through current advances that have been developed for the synthesis of well-defined CO2-based block copolymers, it is possible to overcome some of the weaknesses of polycarbonates derived from both aliphatic and alicyclic epoxides (e.g., low glass transition temperature and brittleness). The utilization of carbon dioxide (CO2) as a monomer for copolymerization with three-membered cyclic ethers, also known as oxiranes or epoxides, has received much renewed interest due to the need for degradable polymeric materials derived from renewable resources. Since the early discovery of the catalytic coupling of CO2 and oxiranes to afford polycarbonates, the area has progressed significantly over the 50 succeeding years. Herein, we describe the currently well-established catalyzed copolymerization process of oxiranes and carbon dioxide utilizing homogeneous metal catalysts. Pertinent to the commercial success of this process is the presence of rapid and reversible chain-transfer reactions that occur in the presence of protic impurities or additives leading to the formation of macropolyols. The focus of this review is to summarize the various synthetic strategies for the production of designer block copolymers for various applications in material science and biomedicine. The utilization of carbon dioxide (CO2) as a monomer for copolymerization with three-membered cyclic ethers, also known as oxiranes or epoxides, has received much renewed interest due to the need for degradable polymeric materials derived from renewable resources. Since the early discovery of the catalytic coupling of CO2 and oxiranes to afford polycarbonates, the area has progressed significantly over the 50 succeeding years. Herein, we describe the currently well-established catalyzed copolymerization process of oxiranes and carbon dioxide utilizing homogeneous metal catalysts. Pertinent to the commercial success of this process is the presence of rapid and reversible chain-transfer reactions that occur in the presence of protic impurities or additives leading to the formation of macropolyols. The focus of this review is to summarize the various synthetic strategies for the production of designer block copolymers for various applications in material science and biomedicine. the purity of block copolymers (i.e., the mole or mass fraction of block copolymers relative to involved homopolymer impurities). a polymerization of the monomer is performed by the propagating species that switches back and forth between the active and dormant states. a CO2 molecule inserted into the M–OR (M, metal; R, alkoxy group) bond forms a growing metallic carbonate (M–OCO–OR) polymer chain. an effective way of altering the physicochemical properties of a polymer via the incorporation of two/three monomers during chain-growth polymerization. ring opening of an epoxide (e.g., PO) occurs at either its methylene carbon or methine carbon via nucleophile attack. a living radical polymerization technique for macromolecular design based on the interchange of xanthates. an emerging polymerization strategy combining ROP and copolymerization to incorporate different monomers into the main chain of a predesigned polymer. for racemic epoxide, the polymerization proceeds by incorporating R-configuration epoxides or S-configuration counterparts; for mesomeric monomer, ring opening occurs at its R-configuration carbon or the S-configuration carbon.