Conformation of ionizable poly Para phenylene ethynylene in dilute solutions

The conformation of dinonyl poly para phenylene ethynylenes (PPEs) with carboxylate side chains, equilibrated in solvents of different quality have been studied using molecular dynamics simulations. PPEs are of interest because of their tunable electro‐optical properties, chemical diversity, and functionality which are essential in wide range of applications. The polymer conformation determines the conjugation length and their assembly mode and affects electro‐optical properties which are critical in current and potential uses. This study investigates the effect of carboxylate fraction on PPEs side chains on the conformation of chains in the dilute limit, in solvents of different quality. The dinonyl PPE chains are modeled atomistically, where the solvents are modeled both implicitly and explicitly. Dinonyl PPEs maintained a stretched out conformation up to a carboxylate fraction f of 0.7 in all solvents studied. The nonyl side chains are extended and oriented away from the PPE backbone in toluene and in implicit good solvent, whereas in water and implicit poor solvent, the nonyl side chains are collapsed toward the PPE backbone. Rotation around the aromatic ring is fast and no long range correlations are seen within the backbone. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 582–588     

Distribution of single DNA molecule electrophoretic mobilities in semidilute and dilute hydroxyethylcellulose solutions

The distribution of center of mass electrophoretic mobility mobilities and normalized migration time of up to 1080 lambda DNA molecules per experiment were measured in both semidilute hydroxyethylcellulose HEC/0.5 x Tris-borate-EDTA (TBE) solutions and dilute HEC/0.5 x TBE solution by high-speed video microscopy. Measurements were made microscopically over a short migration distance in homogeneous DNA HEC/0.5 x TBE solution and after electrophoretic migration of a plug of DNA through 7 cm. Video at 120 frames/s (semidilute HEC solution) and 236 frames/s (dilute HEC solution) allowed visualization with adequate resolution for single molecule mobility measurements. The electrophoretic migration times and band shapes predicted from the measurements corresponded well with those measured by conventional capillary electrophoresis (CE) in both semidilute and dilute HEC. In semidilute solution, the band width predicted by a square root of time scaling is in good agreement with the results of conventional CE. However, in dilute solution the precision of the measurements was not good enough to allow scaled estimates of band widths.     

Dielectric polarization of a partially neutralized poly(methacrylic acid) in dilute aqueous solutions: Conformational transition

Dielectric permittivity ε′ (at a frequency of 1 MHz) of aqueous solutions of a partially neutralized poly(methacrylic acid) Na-PMAA was studied with varying the degree of ionization α_i from 0 to 0.78 and concentrations w ₂ (g/g) from 1.25 × 10^?4 to 6 × 10^?3 at 25°C. It was shown that the concentration dependence of ε′ for Na-PMAA aqueous solutions at all α_i values contains two regions corresponding to different changes in ε′, and the above regions are separated by the crossover point w*₂. In the first region, ε′ increases with the increasing concentration Δε′/Δw ₂ > 0; in the second region, ε′ decreases with the increasing concentration Δε′/Δw ₂ < 0. The sign inversion of Δε′/Δw ₂ is explained by different structures of water and mechanisms of hydration in regions I and II. In the region corresponding to the ascending branch of the ε′-w ₂ curve, the dipole moments of macromolecules per repeating unit, μ = (〈M ²〉/N)^1/2, were calculated according to the Buckingham theory. The μ value is high; as a macromolecule is saturated with ionized units, this value nonmonotonically changes from ～10 D at α_i = 0 to ～18 D at α_i ～ 0.24. This dependence peaks at ～30 D at α_i ～ 0.1. As is assumed, (〈M ²〉/N)^1/2 depends on the vector sum of partial dipole moments of hydrated nonionized monomer units (μ ～10 D) and fluctuation-induced dipole moments of ionized monomer units. The profile of μ as a function of the degree of ionization of Na-PMAA indicates the occurrence of the conformational transition in an individual macromolecule. This transition takes place at the degree of ionization α_i ～ 0.1. An analysis of molecular interactions in the (ionized coil)-solvent system explans the conformational transition in Na-PMAA.     

Flexibility of phenylene oligomers revealed by single molecule spectroscopy

The rigidity of a p-phenylene oligomer (p-terphenyl) has been investigated by single molecule confocal fluorescence microscopy. Two different rylene diimide dyes attached to the terminal positions of the oligomer allowed for wavelength selective excitation of the two chromophores. In combination with polarization modulation the spatial orientation of the transition dipoles of both end groups could be determined independently. We have analyzed 597 single molecules in two different polymer hosts, polymethylmethacrylate and Zeonex. On average we find a 22 degrees deviation from the linear gas phase geometry (T = 0 K), indicating a rather high flexibility of the p-phenylene oligomer independent of the matrix. To substantiate our experimental results, we have performed quantum chemical calculations at the density functional theory level for the molecular geometry and the electronic excitations. Our findings are in agreement with former experiments on the persistence length of poly(p-phenylenes).     

Conformational properties of macromolecules of heterocyclic polyester imides in dilute dichloroacetic acid solutions

Several series of polyester imides (PEIs) were prepared by melt polycondensation of trimellitimidobenzoic acid and acetylated, substituted hydroquinones as well as by solution polycondensation of corresponding dichlorides with hydroquinones. The influence of either phenyl- or tert-butyl substituents at the hydroquinone unit on the hydrodynamic (diffusion and viscometry) and optical [flow (FB) and electrical (EB) birefringence] properties of solutions of these PEIs were investigated. Independent methods for quantitative evaluation of the length of the statistical Kuhn segment A gave values of 14.5 nm (translational friction and electrical birefringence) and 12.0 nm (flow birefringence), respectively. The equilibrium rigidity of PEIs with phenyl and tert-butyl lateral substituents at the para-aromatic chain fragment was comparable. Conformational properties of the PEIs were analyzed, and the conjugation energies of the ester and amide groups for para-aromatic polyesters, PEIs, and structurally similar polyamidobenzoxazoles and polyamidobenzimidazoles were compared. The introduction of the phthalimide ring leads to a decrease of conjugation energy and deviation of the ester group from coplanarity. The Kuhn segment values obtained were useful for calculations of phase diagrams of semiflexible segmented block copolymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 12–24, 2004     

Hydrodynamic properties of rigid pyridine-containing poly(phenylene) dendrimers in solutions

The hydrodynamic properties of pyridine-containing polyphenylene dendrimers of the third and fourth generations in chloroform are studied by photon correlation spectroscopy and viscometry. It has been demonstrated that the hydrodynamic characteristics of these macromolecules in dilute solutions are similar to those of nondraining spheres. The hydrodynamic radius of these dendrimers is shown to be proportional to their molecular mass to a power of 1/3. It has been established that the macromolecules of the dendrimers under examination in solutions conserve the conformation and size over a wide temperature range. The detailed analysis of hydrodynamic data allowed a conclusion concerning an extremely low content of the polymer inside the equivalent sphere for the above dendrimers in solutions. The compounds of interest may be referred to as rigid dendritic systems.     

A viscometric study of dilute aqueous solutions of poly(vinylalcohol)-polyacrylamide mixtures

The viscosity interaction coefficient, k_AB, for the system poly(vinylalcohol)-polyacrylamide-water was determined at 25° by two methods: (a) estimation of the Huggins slope coefficients for mixtures of polymers in different proportions; (b) determination of the intrinsic viscosity of polymer (A) in aqueous solutions of polymer (B). The result, k_AB = 0.3, indicates a low degree of overlapping of unlike polymer molecules.     

Conformational properties of metathesis poly(trimethylsilylnorbornene) in solutions

The hydrodynamic and conformational properties of silicon-containing polynorbornene prepared by metathesis polymerization of 5-trimethylsilylnorbornene in the presence of Grubbs Ru carbene complex were studied by viscometry, isothermal translation diffusion, and centrifugal sedimentation. For the ten-sample homologous series of the polymer, Mark-Kuhn-Houwink relationships correlating the hydrodynamic characteristics of the molecules in toluene with their molecular weight were obtained. Original Russian Text ? N.P. Evlampieva, M.L. Gringol’ts, I.I. Zaitseva, O.V. Okatova, T.S. Dmitrieva, P.P. Khlyabich, E.I. Ryumtsev, 2008, published in Zhurnal Prikladnoi Khimii, 2008, Vol. 81, No. 11, pp. 1899–1905.     

Aggregation of sulfonated poly(p-phenylene terephthalamide) in dilute solutions

The viscosities of dilute solutions of poly(p-phenylene terephthalamide), PPTS, in dimethylacetamide, water, and their mixtures were determined. The reduced viscosity plot in dimethylacetamide shows a negative slope. When the water content in the mixed solvent in 90% or higher, there is an upswing in the reduced viscosity values at concentrations below 0.1 g/dL. The latter behavior suggests a “polyelectrolyte” effect. However, an association model was found to be able to explain the viscosity behaviors in both solvents. ©1995 John Wiley & Sons, Inc.     

Viscometric study of gelatin in dilute aqueous solutions

The viscosities of aqueous solutions of gelatin at different temperatures were carefully measured in a common glass‐capillary Ubbelohde viscometer at dilute to extremely dilute concentrations. The adsorption effect that occurred in the viscosity measurements was theoretically analyzed and discussed. A theory based on Langmuir isotherms could adequately describe the existing data. Some structural information was obtained by the use of an iterative fitting procedure to treat the reduced viscosity data, which disclosed that individual gelatin chains underwent a coil‐to‐helix transition as the solution cooled from 40 to 15 °C. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1804–1812, 2006     

Viscosimetric study of polystyrene polymacromonomer dilute solutions

The viscosimetric behaviour of poly(ω-norbornenyl polystyrene) polymacromonomers is studied in dilute solutions as a function of the degree of polymerisation and the branch molar mass. We emphasise the fact that the exact molar mass characterisation using scattering techniques is illusory, owing to a strong intermolecular contribution in the scattering distribution, as evidenced by neutron scattering. Two characteristic behaviours are evidenced in the viscosimetric dependence versus molar mass of the polymacromonomer and are attributed to their global conformation when they could be considered as spherically or cylindrically symmetric. Moreover for the branch of higher molar mass used an unexplained deviation appears between the two behaviours. Received: 6 May 2000 Accepted: 6 September 2000     

Dynamic viscosity of dilute solutions of poly(L-glutamic acid)

The dynamic viscosity η′ of a dilute solution of poly(L-glutamic acid) (DP = 1370) in a mixed solvent made up of aqueous 0.2M NaCl and dioxane (2:1 by volume) is measured over the pH range 4.2–10 and in the frequency range 2–500 kHz. The frequency dependence of η′ in the helix region (low pH) is interpreted in terms of a model molecule consisting of n rigid helical segments connected by universal joints. The steady-flow viscosity, relaxation time, and high-frequency limiting viscosity at pH 4.75 (helical content 80%) are well explained by this model with n = 5. This value of n is consistent with that estimated from the nucleation parameter σ = 1.4 × 10^?3 obtained from the relation between reduced steady-flow viscosity and helical content. The high-frequency values of η′ in the coil region (high pH) are fitted by Peterlin's theory. The internal viscosity seems to arise in part from the polyelectrolytic character of the molecule. An additional relaxation at low frequencies in the coil region is ascribed to rotation of molecules elongated by the electrostatic interaction. The lower value of reduced steady-flow viscosity in the coil region in the mixed solvent compared with that in water is interpreted in terms of the lower degree of effective ionization and the selective solvation of water by the polypeptide. No anomaly is observed in the helix–coil transition region, indicating that the relaxation time for helix–coil equilibrium is less than 10^?6sec.     

Viscosity-temperature relationships for poly(vinyl chloride)-tetrahydrofuran dilute solutions

The viscous flow parameters for dilute PVC tetrahydrofuran solutions were determined in the temperature range 10–45°. The temperature dependence of the viscosity of the solutions obeys an Arrhenius-type equation. The concentration and the molecular weight dependence of the pre exponential factor of this equation is given by the following relationship:

$\text{A=A}{}_0\text{·}\text{exp}\text{[minus;K}{}_{\mathrm{a}}\text{(c·}\text{M}{}_{\mathrm{w}}\text{)}{}^2\text{]}$

.Both the values of the viscous flow parameters and the mathematical expression of the pre-exponential factor indicate, by comparison with other results, some stiffness of PVC chains in tetrahydrofuran.     

Terephthalamide-nylon single crystals isolated from dilute solutions of hexafluoro-2,2-propandiol

Terephthalamide nylons with two to five carbon atoms in the aliphatic portion of the chain have been crystallized from aqueous solutions of hexafluoro-2,2-propandiol. The 3T and 4T nylons in particular form rodlike crystals. Indications are that these are bundles of cylindrical structures about 50 nm in diameter. Electron diffraction shows the symmetry to be C_2v. Films of the nylons were drawn with great difficulty. The x-ray diffraction on the films is consistent with a monoclinic structure, though the crystal structure could not be positively established. There is some evidence for a polymer chain alignment perpendicular to the long axis of the rods.     

Volumetric properties of dilute aqueous solutions of poly(ethylene glycols)

The densities of aqueous solutions of some poly(ethylene glycols) (mono-, di-, tri-, and tetraethylene glycol, and four carbowaxes with a mean molecular weight ranging from 600 to 15,000), and of di-, tri-, and tetraethylene glycol dimethyl ether have been determined at 25°C, in the concentration range 5–100 g/liter. From these data, the limiting partial specific and/or molar volume of the solute has been calculated. A value of 37.0 ml/monomole has been evaluated for the partial molar volume of the repeating unit ? CH₂CH₂O? , and has been found independent of both terminal groups and chain length. The results suggest that the ethylene units in higher polymers are accessible to the solvent as easily as in oligomers, and support an “open” or extended conformation of the poly(ethylene glycol) chain in aqueous dilute solution. This interpretation has been confirmed by a comparison of the experimental values of partial molar volume with the values calculated by semiempirical models.     

Solution properties of styrene-p-chlorostyrene diblock copolymers—I. Conformational behaviour in dilute solutions

The conformational behaviour of styrene-p-chlorostyrene diblock copolymers in dilute solutions was studied and compared with that of the corresponding triblock copolymers. Eight styrene-p-chlorostyrene diblock copolymers, of almost equimolar composition but with different molecular weights, were prepared using an anionic polymerization technique. The intrinsic viscosities of the copolymers were measured in non-selective solvents, such as toluene and 2-butanone, and in a selective solvent, cumene. The osmotic second virial coefficients of the diblock copolymers were measured in toluene. The data were analysed on the basis of two parameter theories. The unperturbed dimensions for the diblock copolymers can be expressed as a composition average of those for the parent homopolymers and the long-range interaction parameters of the diblock copolymers in toluene, 2-butanone and cumene are smaller than those of the triblock copolymers of the same composition. It means that the diblock copolymer chains in these 3 solvents had a more compact conformation than the triblock copolymers of the same composition and molecular weight.     

Conformational behavior of ethane molecule encapsulated in a nanotube

Investigation of conformation transformations of ethane molecule in single-wall carbon nanotubes by the hybrid DFT method PBE/3z showed that the parameters and the character of the nanotube (length, diameter, open, closed, or semiopened) affect the conformational behavior of the encapsulated molecule leveling the difference in the energy or even resulting in the inversion of the relative stability of the staggered and eclipsed forms.     

Interaction between poly (ethylene oxide) and silica nanoparticles in dilute solutions

A mixed system that includes poly(ethylene oxide) (PEO) and silica (SiO2) nanoparticles is prepared using two mixing methods. The interaction between PEO and the SiO2 nanoparticles in the dilute basic solution is investigated using the dynamic light scattering (DLS) and isothermal titration calorimetry (ITC) techniques. The DLS results show qualitatively that SiO2 nanoparticles interact with both random coils and aggregates of PEO through hydrogen bonding, and PEO-SiO2 complexes are formed. The degree of disaggregation of aggregates of PEO is readily adjusted by changing the concentration of SiO2 nanoparticle suspensions. Moreover, the ITC results also certify quantitatively the interaction between PEO and SiO2 nanoparticle, and give the evidence of formation of PEO-SiO2 complex.