Temperature Dependence of Chain Conformation and Local Rigidity of Isomerized Polyimides in Dimethyl Formamide

• Published in: Chemical research in Chinese universities 2013-10, Vol.29 (5), p.1022-1028
• Main Authors: Liu, Gui-hua, Qiu, Xue-peng, Siddiq, Mohammad, Bo, Shu-qin, Ji, Xiang-ling
• Format: Article
• Language: English
• Subjects: Analytical Chemistry; Chemistry; Chemistry and Materials Science; Chemistry/Food Science; Inorganic Chemistry; Organic Chemistry; Physical Chemistry; 二甲基甲酰胺; 二甲基联苯胺; 刚性; 可溶性聚酰亚胺; 构象异构; 温度依赖性; 相对分子量; 链构象
• ISSN: 1005-9040; 2210-3171
• DOI: 10.1007/s40242-013-2323-4

Temperature dependence of chain conformation and local rigidity of two soluble isomerized polyimides （PIs）, poly（hexafluorodianhydride/3,3＇-dimethylbenzidine）[poly（6FDA/3,3＇-DMB）] and poly（hexafluorodianhy- dride/2,2＇-dimethylbenzidine）[poly（6FDA/2,2＇-DMB）] were investigated by dilute solution viscosity, size exclusion chromatography（SEC） coupled with multi-angle laser light scattering, viscometer, and refractive index detector in dimethylformamide（DMF） with either 0.1 mol/L LiBr or 3.1 mmol/L tetrabutylammonium bromide（TBAB） in the temperature range of 30 to 50 ~C. The scaling relationships of [t/]=K~M~ and Rg=KgMv obtained are employed to in- vestigate the temperature dependence of chain conformation for the two polyimides. The values of a and v are in the range of 0.66--0.69 and 0.53--0.56, respectively, for poly（6FDA/3,3＇-DMB）, meanwhile they are in the range of 0.64--0.68 and 0.53--0.56, respectively, for poly（6FDAJ2,2＇-DMB）. These results reveal that random coil conforma- tions for both Pls are not affected visibly with increasing temperature from 30 ~C to 50 ~C. However, values of more exact intrinsic viscosity from dilute solution measurement indicate there is only tiny coil extension or shrinkage for both PIs with temperature rising. Parameters related to chain flexibility of polymer, including persistence length lp, shift factor ME（relative molecular weight per unit contour length） and backbone diameter d are estimated from the relationship between intrinsic viscosity and molecular weight for the continuous wormlike cylinder model, which indicates that two samples are flexible chains, only the chain of poly（6FDA/3,3＇-DMB） is stiffer than that of poly（6FDA/2,2＇-DMB） slightly.