Making Crystalline CO₂ Copolymer

Carbon dioxide is the main greenhouse gas, but it is also an important, abundant and renewable C1 resource. Among these reactions, the alternating copolymerization of epoxides and CO2 to produce the degradable polycarbonate has been regarded as the most promising green process. Nevertheless, this field suffers from the limited epoxides (mainly focusing on propylene oxide and cyclohexene oxide), poor catalyst activity and low selectivity for polymer formation, and thereby resulting in the slow progress in commercialization. Additionally, in comparison with polyolefins, CO2-based polycarbonates have obvious demerits in the thermal and mechanical properties, significantly affecting their applications.Based on the above problems, this thesis is mainly devoted to expanding the substrates range of meso-epoxides for desymmetrization copolymerization with CO2, affording the stereoregular polycarbonates with novel crystallizability.Synthesis of two novel meso-epoxides:1,4-dihydronaphthalene oxide(CDO) and 1,2-epoxy-4-cyclohexene(CEO).The enantiopure dinuclear Co(Ⅲ)-Salen complex in conjunction with PPNX (PPN= bis(triphenylphosphine)iminium, X= 2,4-dinitrophenoxide) is beneficial for the desymmetrization copolymerization of CO2 with 1,4-dihydronaphthalene oxide or 1,2-epoxy-4-cyclohexene to afford isotactic CO2 copolymers. It was found that the steric hinderance of substituent groups on bimetallic catalyst, reaction temperature, and the used solvents significantly determined the reaction rate, product selectivity, and enantioselectivity. DSC study suggests that the two isotactic CO2 copolemers:CDO-and CEO-based polycarbonates are amorphous. However, it is worth noting that CDO-based polycarbonate possesses a very high Tg of 150 ℃, which is close to bisphenol-A polycarbonates.2. Although isotactic CO2 copolymers from CDO (PCDC) and CEO (PCEC) are amorphous, the simple mixture of equivalent isotactic (R)- and (S)-PCDCs or PCECs gave the crystalline stereocomplexed polycarbonates with enhanced decomposition temperatures. Notably, we are the first time to discover the formation of crystalline hetero-stereocomplexed polymeric materials by the cocrystallization of amorphous isotactic polycarbonates with different chemical structures and opposite configurations.The behaviors in the crystalline state are significantly different from that of the component enantiomeric polymers or their homo-stereocomplexes.