Unit Contour Length Research Articles

Stiff-Chain Behavior of Poly(terephthalamide-P-benzohydrazide) in Dimethyl Sulfoxide

Fifteen fractionated samples of poly(terephthalamide-P-benzohydrazide) (PPAH) ranging in weight-average molecular weight from 2×103 to 6×104 were studied by light scattering, sedimentation equilibrium, and viscometry with dimethyl sulfoxide (DMSO) at 25°C as the solvent. The data obtained for the radius of gyration, the optical anisotropy factor, and the intrinsic viscosity showed the PPAH chain in DMSO to be semiflexible. Analysis of these data in terms of current theories for the Kratky–Porod wormlike chain gave 11.2±0.5 nm, 185±5 nm−1, 0.5 nm, and 2.1 for the persistence length, molar mass per unit contour length, diameter, and optical anisotropy [= 3(α1–α2)/(α1+2α2)] of the PPAH chain in DMSO, respectively. Here, α1 and α2 are, respectively, the longitudinal and transverse polarizabilities per unit contour length of the chain.

Stiff-Chain Behavior of Poly(isophthaloyl-trans-2,5-dimethylpiperazine) in Dilute Solution

For narrow-distribution fractions of poly(isophthaloyl-trans-2,5-dimethylpiperazine) (PIDP) with weight-average molecular weights Mw from 3.7×103 to 2.4×106 g mol−1, z-average mean-square radii of gyration 〈S2〉z and intrinsic viscosities [η] in trifluoroethanol (TFE) and m-cresol were measured at 25°C. From the [η] data for Mw<105 g mol−1, which exhibited the expected stiff-chain behavior, the persistence lengths of PIDP in m-cresol and TFE were determined to be 4.9±0.3 nm and 3.1±0.2 nm, respectively, using Yamakawa–Fujii’s theory for unperturbed wormlike cylinders and assuming the ML and d values estimated previously by Motowoka et al. for poly(phthaloyl-trans-2,5-dimethylpiperazine) and poly-(terephthaloyl-trans-2,5-dimethylpiperazine) in various solvents including m-cresol and TFE. Here ML is the molar mass per unit contour length and d is the diameter of the cylinder. Double-logarithmic plots of ‹S2›z1/2 and [η] against Mw in the region of higher Mw exhibited features usually observed with flexible polymers in good solvents. This result can be explained by the fact that, though semiflexible, the PIDP chain in solution suffers excluded-volume effects if its length exceeds a certain value. In terms of the number of Kuhn’s statistical segments, this critical chain length for PIDP is about 50 in TFE and 150 in m-cresol.

The effect of polydispersity on the evaluation of molecular parameters of a persistent chain from hydrodynamic data

AbstractThe effect of polydispersity on estimates of molecular parameters (statistical segment length, molecular mass per unit contour length and chain thickness) was investigated using viscosity and sedimentation data on polymers with stiff chains. Theoretical functions of Yamakawa and Fujii for a monodisperse polymer and correction functions for polydispersity were used. The effect is very strong in the treatment of sedimentation data, while in the treatment of viscosity data it is still tolerable.

Stiff Chain Behavior of Poly(terephthaloyl-trans-2,5-dimethylpiperazine) in Dilute Solution

For narrow-distribution fractions of poly(isophthaloyl-trans-2,5-dimethylpiperazine) (PIDP) with weight-average molecular weights Mw from 3.7×103 to 2.4×106 g mol−1, z-average mean-square radii of gyration 〈S2〉z and intrinsic viscosities [η] in trifluoroethanol (TFE) and m-cresol were measured at 25°C. From the [η] data for Mw<105 g mol−1, which exhibited the expected stiff-chain behavior, the persistence lengths of PIDP in m-cresol and TFE were determined to be 4.9±0.3 nm and 3.1±0.2 nm, respectively, using Yamakawa–Fujii’s theory for unperturbed wormlike cylinders and assuming the ML and d values estimated previously by Motowoka et al. for poly(phthaloyl-trans-2,5-dimethylpiperazine) and poly-(terephthaloyl-trans-2,5-dimethylpiperazine) in various solvents including m-cresol and TFE. Here ML is the molar mass per unit contour length and d is the diameter of the cylinder. Double-logarithmic plots of ‹S2›z1/2 and [η] against Mw in the region of higher Mw exhibited features usually observed with flexible polymers in good solvents. This result can be explained by the fact that, though semiflexible, the PIDP chain in solution suffers excluded-volume effects if its length exceeds a certain value. In terms of the number of Kuhn’s statistical segments, this critical chain length for PIDP is about 50 in TFE and 150 in m-cresol.