Two soluble isomerized polyimides(PIs)synthesized from 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride(6FDA)with either 2,2′-dimethylbenzidine(2,2′-DMB)or 3,3′-DMB were investigated by means... 相似文献
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 ℃. The scaling relationships of[η]=KηMα and Rg=KgMv obtained are employed to investigate the temperature dependence of chain conformation for the two polyimides. The values of α 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(6FDA/2,2'-DMB). These results reveal that random coil conformations for both PIs are not affected visibly with increasing temperature from 30 ℃ to 50 ℃. 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 ML(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. 相似文献
Summary: The evolution of the various structural units incorporated into hyperbranched polymers formed from the copolymerization of AB2 and AB monomers has been derived by the kinetic scheme. The degree of branching was calculated with a new definition given in this work. The degree of branching monotonously increased with increasing A group conversion (x) and the maximum value could reach 2r/(1 + r)2, where r is the initial fraction of AB2 monomers in the total. Like the average degree of polymerization, the mean‐square radius of gyration of the hyperbranched polymers increased moderately with A group conversion in the range x < 0.9 and displayed an abrupt rise when the copolymerization neared completion. The characteristic ratio of the mean‐square radius of gyration remained constant for the linear polymers. However, the hyperbranched polymers did not possess this character. In comparison with the linear polymerization, the weight average and z‐average degree of polymerization increased due to the addition of the branched monomer units AB2 and the mean‐square radius of gyration decreased quickly for the products of copolymerization.
New equations for static light scattering of dilute binary solutions allow molar mass determination of macromolecules from measurements of scattered intensity ratios between solution and solvent (Ir). In contrast to the standard Carr–Zimm equations, they do not rely on the experimental absolute value of the Rayleigh ratio of a reference liquid. The picture shows a typical plot for the surfactant BRIJ72 in CH2Cl2 (MSupplier=0.359 kg mol?1).
