Yu.V. Brestkin

Rheological properties of an interpolymer complex formed between poly(acrylic acid) and methyl cellulose

Some rheological properties of an interpolymer complex formed in the mixtures of aqueous solutions of poly(acrylic acid) and methyl cellulose are investigated. In a diluted state, the complex exhibits polyelectrolyte properties, and in the shear field, it flows like a pure poly(acrylic acid) solution. From the experimental data obtained from the mixture flow in a longitudinal field, an effective relaxation time was calculated. It turned out to be higher than that for the initial components. The deviation of the experimental values of the viscosity from the calculated additive ones allowed us to determine the critical molecular weight of the poly(acrylic acid) below which the complex is not formed: Mcr ≈ 6 × 104, which is one order of magnitude higher than for the mixtures of spatially complementary macromolecules. The increase of the total polymer concentration in the mixture first leads to an increase of the complex size. Further increase of the polymer concentration and transition to the semidiluted state decreases the complex size and also decreases its solubility in water.

Change in the friction coefficient of the macromolecule during uncoiling in dilute solution

Change in the hydrodynamic interaction of segments of the macromolecule in the longitudinal field on passing from a coil to strainghtened chain is considered. The maximum rise in the friction coefficient of the chain is proportional, in a θ solvent, to √N/ln N (N is the number of segments). The important influence of the logarithmic correction on the kinetic patterns of uncoiling of the macromolecules with N ≈ 104 is demonstrated.

Energy of the hydrothermal transition in cellulose diacetate

Abstract Deformation-time plots relating to a self-elongating sample under differing external loads were the basis on which the energy of the hydrothermal self-elongation of amorphous cellulose diacetate in a water-phenol medium was investigated, and the specific energy of self-elongation and the “negative” longitudinal viscosity were determined. The results are interpreted in terms of a phase transition of the type amorphous state-liquid crystalline state. Prior stretching preceding the self-elongation is regarded as a process that brings the unfolding of some of the chains up to a critical or hypercritical degree of uncoiling and accordingly causes the “selection” of centres of nematic domains that are capable of growth in a particular direction.

Optical heterogeneities of poly(acid)amide concentrates

Abstract The method of turbidity spectra has been used to determine the micron-size heterogeneities present in the prepolymer solutions used to synthesize polyimides (poly-(4,4-hydroxydiphenylene) pyromellitamides) produced by polycondensing the respective monomers in dimethyl fornamide. The proportion by volume of the heterogeneities present in the reaction solutions has been established to consist of admixtures entering with the monomers, and of polymer particles forming by secondary reactions during the polycondensation. The numbers of the heterogeneities per unit of volume and their average radius depend on the varying polycondensation conditions. The most significant and potential source of the heterogeneities is assumed to be the heterogenous distribution of the solid monomer in the space (bulk) of the reaction mixture.

Central spot on the Hν-diffraction patterns of polymer samples containing spherulites☆

On Hν-diffraction patterns of films containing spherulites, in addition to the typical four-petal pattern, scattering is often observed in the central region of the diffraction pattern (so-called central spot) [1–5]. The intensity of the central spot depends on the thickness and history of the sample and passes through a minimum four times when the film is rotated through 360° round a primary beam. Our observations indicate that for films obtained by rapid and irregular cooling of the melt, the intensity of central scattering is comparable with that of spherulitic reflexes. On reducing the rate of cooling the central spot became weaker and with fairly slow reduction in temperature and fairly thin films it disappeared completely. The spot also disappeares on annealing films. However, the central spot again appeared when the annealed specimen was deformed [2, 5]. The intensity of the central spot reached a maximum when the direction of elongation enclosed an angle of 45° with the axes of polaroids and (in the event of fairly low deformation) decreased to zero, when the direction of elongation enclosed an angle of 0 or 90° with the axes. Similar effects are also observed during the deformation of amorphous polymers [6] and are due to the fact that during deformation these materials, on the whole, become optically anisotropic. The well known theory developed by Kuhn and Gruhn [9] enables us to relate the intensity of scattering in the “forward” direction with segmental anisotropy of polymer molecules and their orientation in relation to the axis of elongation. For amorphous crystalline polymers, however, no quantitative relations were derived so far between the intensity of light passed through between the crossed polaroids and the molecular and supermolecular characteristics of the systems. Nevertheless, there are several experimental facts which support the view that during deformation the amorphous-crystalline polymers gradually acquire the properties of a uniaxial crystal and that anisotropy increases in proportion to elongation. Among these facts are: 1) periodicity in changing the intensity of light transmitted in proportion to elongation (Fig. 1a); 2) direct observation of the macroanisotropy of polymers through a quartz prism (Fig. 1, b); 3) agreement (in first approximation) of the angular dependence of the intensity of transmission in crossed polaroids for uniaxially elongated fibres and films with the well known rule of transmission for uniaxial crystals. However, neither the similarity to an optically anisotropic crystal, nor the theory of scattering by a single particle (spherulite) [3, 4] explain the presence of central scattering when the axis of elongation is oriented along the plane of vibration of one of the polaroids. An attempt is made in this paper to give a possible explanation to this phenomenon.

Thermodynamics and dynamics of macromolecules in moderately concentrated polystyrene solutions in bromoform

On introducing into dilute ([η]McM⩽0·6) solution of the M-mer large amounts of the P-mer (M >P) in presence of a network of a “thickening agent” it is possible to study the properties of the M-mer macromolecules in moderately concentrated solutions. The dimensions of the M-mer macromolecules decrease with rise in [η]PcP and the retraction effect for large M is more strongly marked. Change in P does not alter the degree of retraction of the M-mer coils with no change in the nature of the dynamics of the M-mer as compared with the behaviour in the low molecular weight solvent at least up to [η]PcP≈4. In all cases the invariance of the relaxation time relative to [η], η0 and M in the intervals studied of variation in these parameters persists.

Study of modified epoxy polymers using the method of turbidity spectra

Abstract Turbidity spectra were used to study the dispersion of heterophase epoxy compositions obtained from Diane epoxy oligomers with dioctylphthalate and saturated polyether. It was shown that with 15–16 wt.% dioctylphthalate and 10–16 wt.% polyether the epoxide polymer-modifier system undergoes phase separation as a result of which the modifier separates in the form of particles with a radius of 0.1 μm. A study was made of the concentration dependence of the dimension and number of particles of the dispersed phase in the compositions. Satisfactory agreement was derived between results of determining dimensions of particles of the modifier separated using the method of turbidity spectra and phase contrast microscopy.

Study of the structure of interpenetrating polymer systems using the turbidity spectrum and X-ray diffractometry☆

A study was made of the microstructural heterogeneity of interpenetrating polymer systems (IPS) prepared using hexamethylenedi-isocyanate (HMDI)-ethylenesulphide (ES) and 2,4-toluylenedi-isocyanate (2,4-TDI)-propylenesulphide (PrS) by methods involving the turbidity spectrum and X-ray diffractometery. Methodical problems of using the turbidity spectrum to characterize IPS were described. It was shown that IPS are amorphous heterogeneous systems of colloidal level of heterogeneity. The degree of heterogeneity decreases markedly on increasing polyalkylenesulphide content which, apparently, reflects the type of micro-separation in HMDI-ES and 2,4-TDI-PrS systems.

Kinetic conditions for the forced transition of macromolecules of an acrylonitrile copolymer into the uncoiled state

Conclusions-- The transition of the macromolccule of an acrylonitrile copolymer into the uncoiled state in lengthwise flow of aqueous salt solutions at concentrations from 1 · 10−3 to 5 · 10−2 g/cm3 has been studied.-- The critical velocity gradients at which the tangled state of the macromolecules becomes unstable in a lengthwise field have been determined. It has been shown that the values of these agree well with predictions of the theory of semidilute polymer solutions.

Forced transition of cellulose macromolecules into the uncoiled state in amine oxide solutions

Conclusions-- The behavior of polymeric chains in dilute cellulose solutions in triethylamine oxide or in mixtures of this solvent with dimethylformamide under intense lengthwise flow, where the product of the velocity gradient by the chain relaxation time is approximately equal to unity, has been studied. It has been shown that under these conditions, the macromolecules go over into a practically completely uncoiled state.-- A decrease in the viscosity of the solvent as a result of increasing the experimental temperature, or selective solvation of the cellulose by molecules of TEAO, which takes place as a result of using a ternary mixture, shifts the region of the transition in the direction of larger velocity gradients.