The precipitation of cellulose and polyacrylonitrile and its copolymer (PAN) solutions is a well-known process that has been extensively described in numerous studies. It is suggested that “soft” precipitants (aqueous solutions of solvent, alcohols) be used in place of “rigid” ones (water) to control the rate at which solutions precipitate. Diffusion processes can also be controlled by lowering the temperature of the interacting system’s constituent parts. The appearance and structure of the resulting fibers (films) are directly correlated with the rate of coagulation. Adding a composite additive to the solution is an unusual method of altering the rate of polymer phase release. The introduced additive should dissolve in a common solvent, which will ensure the competition of precipitation between the polymer phases. It is shown that using optical methods it is possible to trace the evolution of the polymer phase precipitation and the formed morphology. For 12% solutions of cellulose, PAN and mixed systems in N-methylmorpholine-N-oxide (NMMO) the kinetics of the movement of isoconcentration planes was traced and the growth rates of the precipitated polymer zone were estimated. The introduction of PAN additives into cellulose enables the influence of diffusion processes and minimizes the formation of finger-like defects (vacuoles). When the PAN content in the system is 30% or more, the formation of defects in the precipitated solution is significantly suppressed, which is crucial for achieving a uniform morphology.

Crosslinking process kinetic parameters of mixtures based on low-molecular polyisoprene and MQ‑copolymers have been investigated by means of rotational rheometry. The rheological method allows tracking of the changes in the principal parameters of the system, such as viscosity, dynamic moduli, and the mechanical loss tangent during the entire chemical curing process. The evolution of viscous and viscoelastic properties of the system have been recorded under isothermal conditions as well as under conditions of continuous increase in temperature. Duration of the gelation in the systems has been determined under conditions of shear deformation via extrapolation of the dependence of reciprocal viscosity on time as well as from the crossover of the loss factor in a wide frequency range. Rheological properties of the filled systems about the gelation transition have revealed the power dependence of the dynamic moduli on the frequency, the critical parameter being equal to 0.54 at 100°C. The increase in the fraction of the inorganic component in the MQ-copolymers from 1 : 2 to 1 : 4 has led to an increase in the gelation time.

The rheological and rheokinetic properties of the compositions based on low-molecular rubber polyisoprene and MQ copolymer particles with decyl terminal groups were studied. The effect of the ratio of M and Q units in the copolymer on the rheological and mechanical properties of the compositions was analyzed. An increase in the length of a hydrocarbon substituent in M units was shown to lead to an increase in the affinity of the copolymer to the carbon-chain polymer matrix. An increase in the content of Q units facilitates the growth of the elastic modulus of the cured composites.

The structure and properties of the new material derived from binol (BCA), multifunctional chiral additive to liquid crystals (LC) with a high optical activity and the presence of free carboxylic groups in the molecule, are studied. The analysis of the thermal behavior of BCA is done by means of DSC, rheology methods, dielectric, and IR spectroscopy. The agreement between the rheological and dielectric data indicates the similar relaxation mechanisms, described within the WLF model. The analysis of the IR spectra proves the change in dielectric and rheological parameters induced by the variation in the structure of associates of hydrogen-bonded complexes. The modification of the sizes and quantity of the connected structures with the temperature may result in the possible appearance of nonlinear effects in LC composites associated with the simultaneous complex change in the dielectric and rheological properties.

A series of linear high molecular weight acrylonitrile homopolymers have been synthesized using controlled anionic polymerization. The possibility of producing polyacrylonitrile with a wide range of molecular weights by controlling the concentrations of metal-free initiator and water has been demonstrated. The resulting homopolymers exhibit excellent spinnability.

MQ resins have proved to be promising fillers for obtaining molecular composites based on silicone and carbon-chain rubbers. In the present work, MQ copolymers play the role of a complex filler with an inorganic core (Q unit) and an organic shell (M unit). Copolymers, in which the ratio of M and Q units was 1 : 2, 1 : 3, and 1 : 4, were used as fillers. Grafted methyl and decyl groups made it possible to use the MQ copolymer as a reinforcing filler of a carbon-chain polymer, polyisoprene. The thermal and rheokinetic behavior of filled compositions during the transformation of elastomers into rubbers was studied. Using differential scanning calorimetry and rheology techniques, the temperature parameters of the crosslinked structure formation process were determined and the values of the apparent activation energy of the crosslinking process were calculated. Increasing the proportion of the inorganic component from 1 : 2 to 1 : 4 resulted in an increase in the storage modulus of the crosslinked composites.

The rheological properties, spinnability, and thermal–oxidative stabilization of high-molecular-weight linear polyacrylonitrile (PAN) homopolymers (molecular weights Mη = 90–500 kg/mol), synthesized via a novel metal-free anionic polymerization method, were investigated to reduce coagulant use, enable solvent recycling, and increase the carbon yield of the resulting carbon fibers. This approach enabled the application of the mechanotropic (non-coagulating) spinning method for homopolymer PAN solutions in a wide range of molecular weights and demonstrated the possibility of achieving a high degree of fiber orientation and reasonable mechanical properties. Rheological analysis revealed a significant increase in solution elasticity (G′) with increasing molecular weight, facilitating the choice of optimal deformation rates for effective chain stretching prior to strain-induced phase separation during the eco-friendly spinning of concentrated solutions without using coagulation baths. The possibility of collecting ~80 wt% of the solvent at the first stage of spinning from the as-spun fibers was shown. Transparent, defect-free fibers with a tensile strength of up to 800 MPa and elongation at break of about 20% were spun. Thermal treatment up to 1500 °C yielded carbon fibers with a carbon residue of ~50 wt%, in contrast to ~35 wt% for industrial radically polymerized PAN carbonized under the same conditions.

Optical interferometry has been employed to study the mass exchange processes that accompany the dissolution of PAN ternary copolymer and to determine limiting copolymer concentrations in solutions in different crystal hydrate forms of N-methylmorpholine-N-oxide (NMMO). Turbidity spectra, interferometry, and optical microscopy have been used to study the effect of the nature of a precipitant on the phase transformations in the system during solution coagulation and to find the precipitation numbers upon the addition of water and aqueous NMMO solutions (20–50 wt

Branched polyacrylonitrile has been synthesized via anionic polymerization with the 1,4-diazabicyclo[2.2.2]octane–ethylene oxide initiating system. The degree of branching has been determined by means of NMR spectroscopy and indirectly confirmed by viscometry of the dilute solutions. Solutions of binary mixtures of the branched PAN with the industrial linear polymer in dimethyl sulfoxide with different ratio of the components have been prepared; their rheological behavior has been investigated. It has been shown that the introduction of the branched polymer in a solution of linear PAN allows significant decrease in the mixed solutions viscosity at equal total fraction of the polymer. The addition of branched PAN in a solution of the linear PAN has increased the total concentration of the polymer in the system favoring the increase in the viscosity of the mixed solution, but the viscosity has been significantly lower than this of the equally concentrated solution of the linear polymer. Investigation of the frequency dependences of the components of complex shear modulus of these solutions has revealed that the increase in the viscoelastic properties is mainly due to the increase in the elasticity modulus. Exponent of the frequency dependence of the loss modulus in the terminal zone has not been changed, whereas this of the elasticity modulus has been decreased to 0.4 over the entire range of the ratio between the branched and linear PAN. The specific relaxation time has been decreased with the increase in the fraction of linear PAN. Thermal behavior of linear and branched PAN has been investigated by means of DSC. The performed study has revealed the possibility of preparation of the mixed films and fibers based on linear and branched polyacrylonitrile.

Highly filled vulcanizates based on polyisoprene, organosilicon fillers (polymethylsilsesquioxane and MQ-copolymers), and p-quinone dioxime derivative as a rubber cross-linking agent were prepared. The properties of model rubbers are compared with those formed on the basis of the same elastomer with standard reinforcing fillers, namely, carbon black and aerosil. The effect of fillers on the thermal and mechanical properties of cross-linked objects is estimated. The presence of organosilicon compounds as fillers increases the thermal stability of the composites, and in the case of polymethylsilsesquioxane, both the strength and the tensile modulus of vulcanizates are increased in comparison with rubbers based on standard fillers.

Evolution of the morphology of cellulose solutions in N-methylmorpholine-N-oxide during coagulation with a “soft” coagulant, isobutyl alcohol, at different temperatures is considered. Using optical interferometry and transmitted and scanning electron microscopy the mechanism of phase separation of the system to form a polymer phase is studied depending on the temperature of alcohol. It is shown that, in the case of a room temperature coagulant, a heterogeneous film with a droplet texture enlarging over thickness appears along the precipitation front. At a high temperature of alcohol the coagulation of the solution occurs in two stages. At the first stage the penetration of the coagulant into the jet of spinning solution leading to the formation of vacuoles occurs. The phase separation of the solution proceeds within the vacuoles as microreactors to form a polymer-concentrated shell and a polymer-diluted phase in the vacuole cavity. At the second stage the coagulant diffuses through the vacuole shell into the bulk of the solution and causes its uniform coagulation. The process of vacuole formation is visualized. The transverse cleavage of the film is analyzed by energy dispersive X-ray spectroscopy. The difference in the content of C, N, and O atoms on the walls of vacuoles and in the region of a film with a uniform cellular morphology is established.

This study focuses on the preparation of carbon fiber precursors from solutions of cellulose in N-methylmorpholine-N-oxide with the addition of bis(trimethylsilyl)acetylene, studying their structural features and evaluating thermal behavior. The introduction of a silicon-containing additive into cellulose leads to an increase in the carbon yield during carbonization of composite precursors. The type of the observed peaks on the differential scanning calorimetry (DSC) curves cardinally changes from endo peaks intrinsic for cellulose fibers to the combination of endo and exo peaks for composite fibers. For the first time, coefficient of thermal expansion (CTE) values were obtained for Lyocell fibers and composite fibers with bis(trimethylsilyl)acetylene (BTMSA). The study of the dependence of linear dimensions of the heat treatment fibers on temperature made it possible to determine the relation between thermal expansion coefficients of carbonized fibers and thermogravimetric curves, as well as to reveal the relationship between fiber shrinkage and BTMSA bis(trimethylsilyl)acetylene content. Carbon fibers from composite precursors are obtained at a processing temperature of 1200 °C. A study of the structure of carbon fibers by X-ray diffraction, Raman spectroscopy, and transmission electron microscopy made it possible to determine the amorphous structure of the fibers obtained.

The kinetics of formation of a three-dimensional structure in compositions based on butyl rubber and silicon-containing hyperbranched polymethylsilsesquioxanes and MQ copolymers is studied in comparison with compositions containing common dispersed phases: carbon black and silica. Features of the chemical structure of the synthesized organosilicon polymers make it possible to treat the morphology of their elementary particles as core–shell. The role of an inorganic “core” is played by silica structures, whereas methyl shells should ensure compatibility with the carbochain matrix of the rubber. Quinol ether is used as an agent of crosslinking via double bonds of the isoprene part of the rubber. The crosslinking process is carried out in the mode of continuous heating of compositions with registration of thermal effects by differential scanning calorimetry and dynamic moduli by oscillatory rheometry. The apparent activation energies of the process of chemical crosslinking under nonisothermal conditions are calculated in terms of various models. It is shown that the apparent activation energy of crosslinking is lower for filled systems. This indicates that rubber macromolecules are partially uninvolved in chemical crosslinking as a result of adsorption and loss of relaxation mobility. The adsorption activity of fillers is estimated from a difference in the activation energies of the initial rubber and filled compositions; this parameter is the lowest for polymethylsilsesquioxanes.

The evolution of structural-morphological transformations of cellulose membranes obtained from solutions in N-methylmorpholine-N-oxide through various temperature isobutanol coagulation baths and subsequent treatment with water and their transport properties were studied. Using SEM, it was found that during coagulation in water and drying of the membranes, a uniform monolithic microheterogeneous texture was formed. The replacement of an aqueous precipitation bath with an isobutanol one leads to the formation of a porous structure with wide pore size and shape distributions. With an increase in precipitant temperature in the as-formed membrane, transverse tunnel cavities are formed with respect to the membrane-forming axis, which collapses when the membrane is washed with water, forming a dense texture with a non-uniform membrane volume. The mechanical properties of the obtained membranes were determined and a mechanism is proposed that allows their values to be correlated with structural-morphological and transport properties.

Replacing the aqueous coagulation bath with an alcoholic one during spinning cellulose fibers (films) from solutions in N-methylmorpholine-N-oxide leads to a radical restructuring of the hydrogen bonds net of cellulose and, as a result, to a change in the structure and properties of the resulting material. By the method of optical interferometry, it was possible to identify the intrinsic features of the interaction of the solvent and isomeric alcohols and to construct phase diagrams of binary systems describing the crystalline equilibrium. Knowledge of the phase states of the system at different temperatures renders it possible to exclude the process of solvent crystallization and conduct the spinning in pseudo-homogeneous conditions. The structure and morphology of samples were studied using X-ray diffraction and scanning electron microscopy methods for a specific coagulant. When the solution under certain conditions is coagulated at contact with alcohol, the solvent may be in a glassy state, whereas, when at coagulation in water, an amorphous-crystalline structure is formed. The structural features of cellulose films obtained by coagulation of solutions with water and alcohols help to select potential engineering or functional materials (textile, packaging, membranes, etc.), in which their qualities will manifest to the best extent.

A new method is developed for the production of composite fibers based on cellulose and vinyltriethoxysilane and formed from N -methylmorpholine- N -oxide solutions. Introduction of the organosilicon additive promotes the activation of cellulose pyrolysis processes, and its choice relies on the presence of a double bond in vinyltriethoxysilane, which can be opened when the temperature rises. Mixed solutions are emulsions with labile droplets of the organosilicon liquid that easily change their shape under deformation. The study of the rheological behavior of the mixed solutions of cellulose with vinyltriethoxysilane reveals an unusual character of a change in viscosity with the concentration of vinyltriethoxysilane—with a minimum at 10–15%. From joint solutions by the dry-jet wet method, composite fibers are spun in an aqueous coagulation bath at a rate of 50–70 m/min. The study of their thermal properties shows that in thermolysis vinyltriethoxysilane additives catalyze condensation processes in cellulose and lead to an increase in char yield. Using IR spectroscopy, the combined chemical transformations of cellulose and vinyltriethoxysilane at all stages of the heat treatment of composite fibers up to 1200°C are analyzed for the first time. It is found that during thermolysis the chemical interaction of vinyltriethoxysilane with cellulose occurs and carbon fibers “crosslinked” by silicon carbide fragments are formed.

In order to develop the compositions based on a new generation of environmentally friendly fillers that can improve mechanical characteristics, rubber compounds based on a model butyl rubber, polymethylsilsesquioxane (PMSS), and an MQ copolymer are explored. The effect of the organosilicon fillers on the rheological properties of the resulting rubber-based suspensions is evaluated. It is found that the introduction of 20 wt % of PMSS into the rubber already leads to the viscosity anomaly, while the MQ copolymer does not produce such an effect. The variation range of the moduli during a cross-linking process is significantly higher for the compositions containing the MQ resin. At the same time, absolute magnitudes of the storage and loss moduli for the systems with PMSS are much higher. One of the reasons for this behavior may be stronger adsorption of the rubber molecules on PMSS particles, which leads to the formation of a mixed network of the rubber with physical and chemical bonds.