Selective transformation of CO2 into degradable polycarbonates by the alternating copolymerization with epoxides represents an important green polymerization process.Although the commercialization of CO2 copolymers (CO2-based polycarbonates) has already made a certain progress in recent years

the further development of this green technology is suffering from material performance as well as product type etc.The main problem is that all the previously reported CO2 copolymers are amorphous and have low glass transition temperatures

which make the strength sharply decrease at high temperatures.This paper focuses on the recent progress of the stereospecific copolymerization of CO2 and epoxides

including design of highly stereoregular catalysts based on mononuclear and dinuclear cobalt(Ⅲ) complexes

and discovery of various crystalline CO\-2-based polycarbonates.Although various highly isotactic CO2 copolymers from terminal epoxides were prepared

only two of them were found to be crystallized.On the contrary

most highly isotactic CO2 copolymers from meso-epoxides are typical semi-crystalline materials

possessing the melting points of 179-257℃

dependent on the employed meso-epoxides. Notably

various crystalline stereocomplexes were found to be formed in the blend of equivalent crystalline or amorphous isotactic (R)-and (S)-polycarbonates.They show the enhanced thermal stability and new crystalline behavior

significantly distinct from the component enantiomer.Moreover

the cocrystallization of amorphous isotactic polycarbonates with different chemical structures and opposite configurations provided novel crystalline hetero-stereocomplexed polymeric materials.Furthermore

racemic bimetallic cobalt catalyst system mediated stereoselective copolymerization of CO2 and meso-epoxides afforded novel intramolecular stereocomplexed polycarbonates

due to highly enantioselective chain growth in an enantiopure catalyst molecule and the copolymer-chain transfer between different configuration catalyst molecules resulting in the formation of the isotactic multiblock polycarbonates.