Hydrodynamic and conformational properties of cellulose myristate molecules in solution

Cellulose myristate samples with a degree of substitution of 230–250 have been studied by the methods of molecular hydrodynamics (viscometry, analytical ultracentrifugation (flotation), and isothermal translational diffusion) in chloroform in the range M = (56–652) × 10³. The experimental evidence has been interpreted within the framework of the generalized wormlike Yamakawa-Fuji model with the following parameters: the persistence length a = 115 × 10^?8 cm, the chain diameter d = 45 × 10^?8 cm, and the molecular mass per unit chain length M _L = 270 × 10⁸ cm^?1. It has been inferred that the polymer dissolves in chloroform in the form of dimers.     

Hydrodynamic and conformational properties of cellulose valerate molecules in dilute solution

Using the methods of molecular hydrodynamics, structural-conformational studies have been performed for a number of cellulose valerate and acetovalerate samples in the molecular-mass range M = (58.1–464.3) × 10³ and with a mean degree of substitution of 182.4 with respect to valeric acid isomers. The conformations of valerate-substituted cellulose molecules are characterized by an increased local packing density of monomer units. The molecular conformations are quantitatively described in terms of the helix formed by the succession of vectors connecting glycoside oxygens of a chain. The molecular-hydrodynamic and conformational characteristics of cellulose valerate are compared with the corresponding characteristics of cellulose myristate.     

Hydrodynamic, conformational, and optical properties of cellulose tridecanoate molecules in solutions

Cellulose tridecanoates of various molecular weights were synthesized, and their characteristics in chloroform and tetrachloroethane solutions were studied by methods of translational diffusion, velocity sedimentation, flow birefringence (Maxwell’s method), and viscometry. The effects of solvent and temperature on the conformational characteristics of the macromolecules under consideration were examined. The anisotropy of the monomeric unit of cellulose tridecanoates was studied, and the contribution of pendant chains to the optical anisotropy of macromolecules of cellulose esters with aliphatic substituents was analyzed.     

Phase transitions in solutions of hydroxypropoyl cellulose and cyanoethyl cellulose

LC phase transitions in mixtures of cyanoethyl cellulose and hydroxypropyl cellulose with different solvents have been studied by the cloud point and polarization microscopy methods and polarization photoelectric measurements. It has been found that, as the solvent polarity is decreased and the molecular mass of a polymer is increased, boundary curves delimiting the regions of isotropic and anisotropic solutions shift to the region of lower concentrations.     

Hydrodynamic properties and conformation of molecules of para- and meta-isomers of polyoxyphenylbenzoxazoleterephthalamide

Translational diffusion and intrinsic viscosity in 96% H₂SO₄ have been investigated for 20 samples of the para-isomer of polyoxyphenylbenzoxazoleterephthalamide (PpOPhBT) and 17 samples of its meta-isomer (PmOPhBT). The Mark-Kuhn equations have been obtained. The equilibrium rigidity of macromolecules in solution, calculated by using the wormlike chain theory, was characterized for PpOPhBT by the length of the Kuhn segment $\text{A = 320}\text{A}\text{?}$, the number of monomer units in a segment s = 17 and the coefficient of hindrance to intramolecular rotation in the chain σ = 1.5. For PmOPhBT the corresponding values are: $\text{A = 96}\text{A}\text{?}$, s = 5.9 and σ = 1.6. Analysis of flexibility mechanisms was carried out for PpOPhBT and PmOPhBT chains in solution.     

Structure and solution properties of cyanoethyl celluloses synthesized in LiOH/urea aqueous solution

Cyanoethyl celluloses (CECs) with different degree of substitution (DS) were synthesized by homogeneous reaction of cellulose (cotton linter pulp and absorbent cotton) with acrylonitrile (AN) in LiOH/urea aqueous solutions. The reaction showed quick reactivity and high transfer efficiency of etherification agent. The DS values of CECs were controlled by varying the molar ratio of AN to anhydroglucose unit (AGU) and the cellulose concentration. The DS values of the CEC-1–CEC-10 increased from 0.27 to 1.78 with increasing molar ratio of AN to AGU from 0.5:1 to 9:1. While the CEC-11–CEC-21 with DS values of 0.26–1.81 could be obtained by adjusting the molar ratio from 1:1 to 27:1. The relative reactivity of hydroxyl groups is in the order of C-6 > C-2 > C-3. The DS values of the water-soluble derivatives are in the range of 0.47–1.01. As the DS values increase to 1.37, CEC samples can not be dissolved in water or dilute alkali solution, but have good solubility in organic solvents, such as DMSO, DMF and pyridine. The dilute solution properties and molecular parameters of the CEC samples were studied by static light scattering and dynamic light scattering. The results indicated that the water-soluble samples could form a small number of aggregates spontaneously in 0.9 wt% NaCl aqueous solution, while the water-insoluble samples showed extended stiff chains in 0.5% LiCl–DMAc.     

Hydrodynamic and conformational properties of dendron-modified polystyrene molecules

The molecular characteristics of polystyrene modified by the Frechet type dendrons of 1–4 generations were studied in tetrahydrofuran by viscometry, isothermal diffusion, electric birefringence, and dynamic and static light scattering. It was shown that dendronized polystyrene molecules whose polymerization degree changes from 1640 to 930 with an increase in the generation number of dendrons occur in the coillike conformation. The equilibrium rigidity of macromolecules tends to increase with increasing the generation number of dendrons. The Kuhn segment length grows from 3.9 nm for polystyrene molecules modified by dendrons of the first generation to 23.3 nm for polystyrene molecules carrying dendrons of the fourth generation.     

Solution properties and chain conformation characteristics of cellulose tricarbanilate

Fractions of two cellulose tricarbanilate samples were characterized by light-scattering (weight-average molecular weight, second virial coefficient, mean-square radius of gyration), gel permeation chromatography (polydispersity index), and viscometry (intrinsic viscosity) in tetrahydrofuran and acetone. The intrinsic viscosity data were analyzed in terms of the theory developed for the continuous wormlike cylinder model, and the chain parameters (Kuhn statistical segment length λ^?1, chain diameter d, and shift factor M_L) were evaluated. The molecular-weight dependence of the mean-square radius of gyration in tetrahydrofuran was calculated for the Kratky—Porod chain model and compared with the experimental results. Data on the intrinsic viscosity and radii of gyration for other solvents at temperatures from 0 to 100°C were analyzed in the same way, and the effects of solvent and temperature on the statistical segment length were evaluated. Polymer—solvent interaction parameters were estimated from the second virial coefficients.     

Phase transitions in liquid-crystalline cyanoethyl cellulose solutions in magnetic field

The cloud-point method and polarization microscopy have been used to investigate the phase transitions and the phase state of cyanoethyl cellulose-dimethylacetamide and cyanoethyl cellulose-dimethylformamide systems in the presence and absence of magnetic field with the help of polarization photoelectric and magnetic setups. The temperature-concentration region of the existence of the liquid-crystalline phase in solutions widens in the magnetic field; the higher the field strength and polymer concentration, the more pronounced this widening. Cyanoethyl cellulose solutions are found to possess “memory”: after the magnetic field is switched-off, the orientation of macromolecules and the increased phase transition temperature are preserved for many hours.     

Hydrodynamic modeling of diffusion tensor properties of flexible molecules

We present a computationally efficient implementation of hydrodynamic modeling for the evaluation of diffusion tensors of molecules with internal degrees of freedom, adapted to take into account information from linear scaling computations of solvent accessible surfaces implemented in the framework of last generation continuum solvent models. Torsional angles are taken also explicitly into account, while retaining correct hydrodynamic interactions. A comparison with literature data is presented to prove the effectiveness of the approach for a wide range of molecular dimensions and solvent environments.     

Hydrodynamic properties of regular star-branched polymer in dilute solution

We calculate quantities such as g = [η]_b/[η]_l and h = (f_t)_b/(f_t)_t for regular star-branched polymer with and without excluded volume. We have applied a numerical method introduced by Barrett for the linear chain and have solved the integral equations which are conducive to calculate the translational coefficient friction and the intrinsic viscosity in the Kirkwood-Riseman theory. We utilize preaveraging but avoid other approximations. In general, we obtain values which have a better accord with experimental data than traditional Kirkwood-Riseman and Zimm-Kilb formulas. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys, 35: 563–567, 1997     

Sorption of vapors of organic solvents with cyanoethyl hydroxyethyl cellulose

The interaction of cyanoethyl hydroxyethyl cellulose with acetone, methylene chloride, and trifluoroacetic acid in the temperature range 10–50°C was studied by the solvent vapor sorption technique. The temperature and concentration dependences of the Flory-Huggins parameter for polymer-solvent interaction Z₁ and the mechanism of the structural rearrangement in the systems were determined.     

Dilute solution properties of sodium cellulose disulphate

Sodium cellulose sulphate (NaCaS), with degree of substitution (DS) of 1.90, was synthesized by reacting samples of cellulose, covering a wide range of average molecular weight, with S03/dimethyl formamide complex. A solution of NaCS in 0.5 M aq. NaCl was studied by solution viscometry, light scattering and membrane osmometry. The solution was dialysed against solvent. The following MarkHouwink-Sakurada equation and relation between the z-average radius of gyration and weightaverage molecular weight, Mw, were established for $\text{7.2 × 10}{}^4\text{?}\text{M}{}_{\mathrm{w}}\text{? 1.5 × 10}{}^6\text{at 25°}$.The NaCS with salt system was analysed according to the theory of linear non-ionic polymers. Flory's viscosity parameter φ is significantly molecular weight dependent. The partially free draining effect and the excluded volume effect were estimated and the former predominated. The unperturbed chain can be regarded as Gaussian and its dimension A was found to be 1.21 × 10^?8 cmand the conformation parameter a was 2.9.     

Hydrodynamic properties and equilibrium rigidity of polyamidobenzimidazole molecules in dimethylacetamide and sulphuric acid

Translational diffusion, velocity sedimentation and viscometry of polyamidobenzimidazole (PABI) solutions in the range of M = (1–61) · 10³ have been investigated in N,N-dimethylacetamide (DMA) and 98% H₂SO₄. The dependences of D₀, S₀ and [η] on M were obtained. Tsvetkov-Klenin's hydrodynamic invariant was found to be $\text{A}{}_0\text{= 3.55 · 10}{}^{\mathrm{?10}}\text{erg deg}{}^{\mathrm{?1}}\text{mol}{}^{\mathrm{<mtext>?</mtext><mtext>1</mtext><mtext>3</mtext>}}$. The equilibrium rigidity of PABI molecules was characterized by the length of the Kuhn segment $\text{A = 250 ± 100}\text{A}\text{?}$. The chain diameter was $\text{7 ± 4}\text{A}\text{?}$. The values of A in 98% H₂SO₄ and in an aprotic solvent, DMA, were virtually identical, implying that the rigid-chain conformation of PABI molecules in 98% H₂SO₄ is due to their geometrical structure rather than to the protonization of amide bonds. The significance of the latter evidently increases in PABI solutions in 100% H₂SO₄ in which A is 1.5 times as high. The decrease in rigidity of PABI as compared to that of poly-p-phenylene terephthalamide ($\text{A = 400 ± 100}\text{A}\text{?}$) is in reasonable agreement with the presence of imidazole rings in PABI molecules. The presence of these rings results in kinks in the PABI chain with angles of about 30° and hence, in the depature from parallelism of rotating bonds.     

Rotary friction,dipole moments,conformation and rigidity of polybutylisocyanate molecules in solution

Experimental data on the dependence of the rotatory diffusion coefficients and dipole moments on molecular weight and the theory of hydrodynamic properties and of the size of wormlike chains were used for determining the main conformational characteristics of the polyisocyanate chain S is the number of molecular units in a segment, λ is the length of the projection of the monomer unit on the axis of the molecule, and μ_o is the dipole moment of the monomer unit. The values of S and λ agree with those found previously by hydrodynamic methods. It was shown that the flat cis-structure of the polyisocyanate chain corresponds to values of λ = 2 × 10^?8cm andμ_o = 1·8D. Analysis of experimental data indicates that dimensions of “geometrical” and “electrical” segments in the PBIC chain are identical.     

Synthesis of cyanoethyl ethers of cellulose from flax fiber production waste

Conditions of preparation of cellulose cyanoethyl ethers with different degrees of substitution, based flax fiber production waste were examined. The chemical structure of the resulting cellulose ethers and variation of the structure of the cellulose materials during cyanoethylation were examined by IR-Fourier spectroscopy and X-ray diffraction analysis. The degree of substitution of cellulose ethers was examined in relation to cyanoethylation conditions and chemical composition of the initial cellulose materials.     

Phase transitions of liquid crystalline cyanoethyl cellulose solutions under static conditions and in shear field

Phase transitions in the systems cyanoethyl cellulose-DMF, cyanoethyl cellulose-DMAA, and cyanoethyl cellulose-(trifluoroacetic acid + methylene chloride) were studied by means of the cloud-point and polarization microscopy techniques, as well as with a photoelectric polarization unit and a modified plasticorder. It was shown that the LC phase appears at higher concentrations and lower temperatures as the polarity of solvent molecules increases. The shear deformation of cyanoethyl cellulose solutions in DMF and DMAA results in the expansion of the temperature-concentration region of existence of the LC phase. The effect of shear field on phase transitions in cyanoethyl cellulose solutions is nonmonotonic in character.     

Hydrodynamic properties and conformation of poly(3‐hexylthiophene) in dilute solutions

Conducting polymers demonstrate low solubility in organic solvents. Introducing aliphatic substituents into polymer chains improves their solubility, but may also lead to changes in conformational characteristics of macromolecules. In the present work, the studies of hydrodynamic properties and conformational characteristics of comb‐shaped poly(3‐hexylthiophene) with aliphatic side substituents were carried out in chloroform solutions. Conformational analysis of the studied macromolecules was performed for the first time using homologous series with a wide range of molecular weights of the polymers in dilute solutions. The hydrodynamic properties of these macromolecules were interpreted using the worm‐like spherocylinder model and the straight spherocylinder model. The projection of the monomer unit in the direction of the main polymer chain λ = 0.37 nm was determined experimentally. The following parameters of poly(3‐hexylthiophene) were characterized and quantified: equilibrium rigidity (Kuhn segment length) А = 6.7 nm and hydrodynamic diameter of a polymer chain d = 0.6 nm. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 875–883     

Hydrodynamic invariant of polymer molecules

The theories of hydrodynamic properties of macromolecules in solution leading to an invariant relationship between the values of the intrinsic viscosity, [η], the molecular weight, M, and the translational friction coefficient of the molecule, f, have been considered. The review of experimental data comprising as much as about 2000 fractions of various polymers suggests that for all flexible-chain and moderately rigid-chain molecules the hydrodynamic parameter A₀ = kη₀(M[η]/100)^1/3f^?1 is actually an invariant independent of the chain length and the thermodynamic strength of the solvent and for moderately polydisperse samples also independent of the degree of their polydispersity. For polymers with very rigid chains the parameter A₀ has a high value over the experimentally investigated range of M. These conclusions make it possible to recommend the use of the following average experimental values of the invariant A₀ for the determination of M of polymers from the values of [η] and f: for flexible-chain and synthetic polymers with moderately high chain rigidity (3.2 ± 0.2) · 10^?10, for polymers with high chain rigidity (3.7 ± 0.4) · 10^?10, and for cellulose derivatives and other polysaccharides with molecular dispersity of nonelectrolyte solutions (3.30 ± 0.30) · 10^?10 erg deg^?1 mol^?1/3. The fact that the experimental value of A₀ = 3.2 · 10^?10 does not coincide with the value of A_∞ = 3.8 · 10^?10 erg deg^?1 mol^?1/3 predicted by the theories of translational friction and viscosity of macromolecules implies that the theoretical values of P_∞ = 5.11 and Φ_∞ = 2.8 · 10²³ mol^?1 are mutually incompatible and these theories require further development.