CO2-based stereocomplexed polycarbonates derived from the intermolecularly interlocked interaction between the enantiopure polymers with the opposite configuration exhibit high crystallinity, excellent thermal and mec...CO2-based stereocomplexed polycarbonates derived from the intermolecularly interlocked interaction between the enantiopure polymers with the opposite configuration exhibit high crystallinity, excellent thermal and mechanical stabilities. Deep insights into the mechanism of stereocomplexation are of particular importance to the design and manufacture of new promising and sustainable polycarbonates with enhanced physicochemical properties. Our solid-state NMR experiments linking with DFT computations clearly reveal the specific chain-chain interactions in a typical stereocomplexed poly（4,4-dimethyl-3,5,8-trioxabicyclo[5.1.0] octane carbonate）（PCXC）.13C CP/MAS NMR,1H DUMBO MAS NMR and 13C/1H relaxation-time measurements indicate that the formation of stereocomplex reduces the local mobilities of carbonyl, methine and methylene groups in each chain of PCXC significantly. Through a combination of two-dimensional 1H-13C HETCOR NMR and DFT calculation analysis, the cis-/trans-conformations and packing models of PCXC chains in the amorphous, enantionpure isotactic and stereocomplexed polycarbonates are identified. The splitting of 13C and 1H NMR chemical shifts of methine groups in the backbone carbon region demonstrates the ordered interlock interactions between the R-and S-chain in the stereocomplexed PCXC.展开更多
Stereoselective interaction was observed in the mixture of enantiopure gradient polycarbonate(denoted as PCOPC-g-PCPC, originated from the enantioselective terpolymerization of CO2, 3,4-epoxytetrahydrofuran(COPO) and ...Stereoselective interaction was observed in the mixture of enantiopure gradient polycarbonate(denoted as PCOPC-g-PCPC, originated from the enantioselective terpolymerization of CO2, 3,4-epoxytetrahydrofuran(COPO) and cyclopentene oxide(CPO)) and various isotactic polycarbonates with opposite configuration in chloroform solution. The resultant crystalline stereocomplexes exhibit enhanced thermal stability and new crystalline behaviors, significantly distinct from their parent polymers. It was found that the cocrystallization selectively occurred between(R)-PCOPC(CO_2/COPO copolymer) and(S)-PCOPC-enriched segment in the gradient terpolymer(S)-PCOPC-g-PCPC, while(R)-PCPC(CO_2/CPO copolymer) selectively complexed with(S)-PCPC-enriched segment. No stereocomplexation was observed between(S)-PCOPC-g-PCPC and(S)-PCOPC or(S)-PCPC. This study is beneficial to finding new routes to prepare various semicrystalline materials having a wide variety of physical properties and degradability.展开更多
基金financial supports from the National Natural Science Foundation of China (Nos. 21373035, 21673027 and 21603022)the Fundamental Research Funds for the Central Universities in China (Nos. DUT16RC(3)002 and DUT17TD04)
文摘CO2-based stereocomplexed polycarbonates derived from the intermolecularly interlocked interaction between the enantiopure polymers with the opposite configuration exhibit high crystallinity, excellent thermal and mechanical stabilities. Deep insights into the mechanism of stereocomplexation are of particular importance to the design and manufacture of new promising and sustainable polycarbonates with enhanced physicochemical properties. Our solid-state NMR experiments linking with DFT computations clearly reveal the specific chain-chain interactions in a typical stereocomplexed poly（4,4-dimethyl-3,5,8-trioxabicyclo[5.1.0] octane carbonate）（PCXC）.13C CP/MAS NMR,1H DUMBO MAS NMR and 13C/1H relaxation-time measurements indicate that the formation of stereocomplex reduces the local mobilities of carbonyl, methine and methylene groups in each chain of PCXC significantly. Through a combination of two-dimensional 1H-13C HETCOR NMR and DFT calculation analysis, the cis-/trans-conformations and packing models of PCXC chains in the amorphous, enantionpure isotactic and stereocomplexed polycarbonates are identified. The splitting of 13C and 1H NMR chemical shifts of methine groups in the backbone carbon region demonstrates the ordered interlock interactions between the R-and S-chain in the stereocomplexed PCXC.
基金supported by the National Natural Science Foundation of China (21134002, 21504011)the Specialized Research Fund for the Doctoral Program of Higher Education (20130041130004)the Chang Jiang Scholars Program (T2011056) from Ministry of Education of the People’s Republic of China
文摘Stereoselective interaction was observed in the mixture of enantiopure gradient polycarbonate(denoted as PCOPC-g-PCPC, originated from the enantioselective terpolymerization of CO2, 3,4-epoxytetrahydrofuran(COPO) and cyclopentene oxide(CPO)) and various isotactic polycarbonates with opposite configuration in chloroform solution. The resultant crystalline stereocomplexes exhibit enhanced thermal stability and new crystalline behaviors, significantly distinct from their parent polymers. It was found that the cocrystallization selectively occurred between(R)-PCOPC(CO_2/COPO copolymer) and(S)-PCOPC-enriched segment in the gradient terpolymer(S)-PCOPC-g-PCPC, while(R)-PCPC(CO_2/CPO copolymer) selectively complexed with(S)-PCPC-enriched segment. No stereocomplexation was observed between(S)-PCOPC-g-PCPC and(S)-PCOPC or(S)-PCPC. This study is beneficial to finding new routes to prepare various semicrystalline materials having a wide variety of physical properties and degradability.
