The mechanical properties of fibers were notably improved by incorporating 2,2＇-bis（trifluoromethyl）benzidine（TFMB） into 3,3＇,4,4＇-biphenyltetracarboxylic dianhydride（s-BPDA） and p-phenylenediamine（PPD） bac...The mechanical properties of fibers were notably improved by incorporating 2,2＇-bis（trifluoromethyl）benzidine（TFMB） into 3,3＇,4,4＇-biphenyltetracarboxylic dianhydride（s-BPDA） and p-phenylenediamine（PPD） backbone.The best strength and modulus of BPDA/PPD/TFMB polyimide（PI） fiber（diamine molar ratio of PPD/TFMB= 90/10） were 1.60 and 90 GPa,respectively,which was over two times that of BPDA/PPD PI fiber.SEM image showed that the cross-section of fibers at each stage was round and voids free.Besides,the ＂skin-core＂ and microfibrillar structure were not observed.The thermal properties of PI fibers were also investigated.The results showed that the fibers owned excellent thermal stability,moreover,the structural homogeneity of fibers were significantly improved by heat-drawn stage.The T g values were found to be around 300 °C by dynamic mechanical analysis（DMA）.Wide angle X-ray diffraction（WAXD） and small angle X-ray scattering（SAXS） experiments indicated that the order degree of longitudinal and lateral stacks,the molecular orientation and the structural homogeneity of fibers were improved in the preparation process of fibers.展开更多
With methyl ester of N-acylated L-3-（3,4-dihydroxyphenyl）alanine（L-DOPA） as starting material, racemic derivatives of 3-hydroxymethyl-1,2,3,4-tetrahydroisoquinoline were obtained with cyclization by Bischler-Napie...With methyl ester of N-acylated L-3-（3,4-dihydroxyphenyl）alanine（L-DOPA） as starting material, racemic derivatives of 3-hydroxymethyl-1,2,3,4-tetrahydroisoquinoline were obtained with cyclization by Bischler-Napie- ralski（BN） reaction followed by reduction of methyl ester group to hydroxymethyl, while the optical pure enantiomers were prepared by the reduction of the methyl ester group to hydroxymethyl prior to cyclization with BN reaction. Racemerization took place in the BN stage in the presence of methyl ester, an electron-withdrawing group adjacent to chiral center. Therefore, the sequence of synthetic stages of cyclization and reduction, and subsequently whether there is electron-withdrawing group or not determines the chiral optical activity of the products.展开更多
基金Supported by the Science & Technology Development Program of Jilin Province,China(No.20100537)
文摘The mechanical properties of fibers were notably improved by incorporating 2,2＇-bis（trifluoromethyl）benzidine（TFMB） into 3,3＇,4,4＇-biphenyltetracarboxylic dianhydride（s-BPDA） and p-phenylenediamine（PPD） backbone.The best strength and modulus of BPDA/PPD/TFMB polyimide（PI） fiber（diamine molar ratio of PPD/TFMB= 90/10） were 1.60 and 90 GPa,respectively,which was over two times that of BPDA/PPD PI fiber.SEM image showed that the cross-section of fibers at each stage was round and voids free.Besides,the ＂skin-core＂ and microfibrillar structure were not observed.The thermal properties of PI fibers were also investigated.The results showed that the fibers owned excellent thermal stability,moreover,the structural homogeneity of fibers were significantly improved by heat-drawn stage.The T g values were found to be around 300 °C by dynamic mechanical analysis（DMA）.Wide angle X-ray diffraction（WAXD） and small angle X-ray scattering（SAXS） experiments indicated that the order degree of longitudinal and lateral stacks,the molecular orientation and the structural homogeneity of fibers were improved in the preparation process of fibers.
文摘With methyl ester of N-acylated L-3-（3,4-dihydroxyphenyl）alanine（L-DOPA） as starting material, racemic derivatives of 3-hydroxymethyl-1,2,3,4-tetrahydroisoquinoline were obtained with cyclization by Bischler-Napie- ralski（BN） reaction followed by reduction of methyl ester group to hydroxymethyl, while the optical pure enantiomers were prepared by the reduction of the methyl ester group to hydroxymethyl prior to cyclization with BN reaction. Racemerization took place in the BN stage in the presence of methyl ester, an electron-withdrawing group adjacent to chiral center. Therefore, the sequence of synthetic stages of cyclization and reduction, and subsequently whether there is electron-withdrawing group or not determines the chiral optical activity of the products.
