V. P. Grachev

Synthesis, Structure, and Properties of Branched Polymethacrylates

The methacrylate: branching agent: chain growth regulator optimal ratios that allow the synthesis of branched polymethacrylates via the crosslinking free-radical copolymerization under the regime of conventional or catalytic chain transfer have been estimated. Relationships between the molecular-mass characteristics of the copolymers, their content of intact C=C bonds, the composition of the starting monomer mixture, and the structure of the branching agent and polymer chain growth regulator have been established. The rheological properties of the branched MMA-based copolymers have been studied. It has been shown that the copolymers are characterized by a weaker dependence of reduced viscosity on the polymer concentration in solution than that for the linear PMMA. The diffusion-sorption behavior of the branched polymethacrylates is determined by the content of the branching agent in them.

Effect of the nature of a solvent on pseudoliving free-radical polymerization of styrene mediated by TEMPO

The kinetics and mechanism of the pseudoliving free-radical polymerization of styrene are studied for the first time under the conditions of reversible inhibition by TEMPO nitroxides. An abnormal decline in the reduced rate of polymerization, which is inconsistent with a decrease in the concentration of the monomer, and an increase in the steady-state concentration of the free nitroxide are discovered. The main quantitative characteristics of the pseudoliving process are determined, namely, the rate constants of reinitiation and reversible recombination, and the constant of pseudoliving equilibrium between dormant and growing chains. It is shown that the polarity of a medium and the concentration of the monomer determine the character of polymerization in a solution: With an increase in the polarity of the solvent, the pseudoliving equilibrium constant increases, the reduced rate of styrene polymerization decreases, and the molecularmass-distribution of the polymer formed at initial conversions narrows. The smaller the concentration of styrene in the reaction system, the more pronounced the above differences associated with the solvent nature.

Three-dimensional free-radical polymerization of vinyl monomers in the presence of oxygen as a new method of preparing hyperbranched polymers: A theoretical calculation

Hyperbranched macromolecules have been first synthesized by the three-dimensional free-radical polymerization of vinyl monomers in the presence of oxygen, which is known to be a strong inhibitor of freeradical chain processes. The inhibition of free-radical polymerization by molecular oxygen results in the shortening of primary polymer chains with pendant double bonds. As a consequence, the formation of insoluble gel, which develops at conversions of less than 1%, when the crosslinking free-radical polymerization is carried out under ordinary conditions, may be avoided up to a conversion of 100%. In terms of the kinetic scheme, including nearly 100 elementary reactions, the effects of temperature and concentration of reagents on the kinetic parameters of the process and the structural parameters of hyperbranched polymers based on methacrylate and styrene-like monomers have been studied. Optimal conditions that make it possible to synthesize hyperbranched polymers of the desired architecture and functionality at a sufficiently high yield, which are specified by the occurrence of oxygen-containing groups in primary polymer chains and at its ends, have been estimated.

Comments on M.Yu. Zaremski, Chen Xin, A.P. Orlova, I.V. Blagodatskikh, and V.B. Golubev’s Paper “General Features and Specifics of the Kinetics of the Pseudoliving Radical Polymerization of 4-Vinylpyridine and Styrene Mediated by TEMPO”

It is shown through a numerical experiment that, in the presence of extra (spontaneous) initiation, the equilibrium constant and the ratio between the rates of quadratic and reversible terminations cannot affect the rate of pseudoliving radical polymerization. The kinetics of the process in the steady-state region is determined only by the ratio between the rates of additional initiation and quadratic chain termination. Discrepancies between experimental data and theory must be explained with allowance for side reactions that can occur in these complex systems rather than via re-examination of the reliably verified mechanism of pseudo-living radical polymerization.

The kinetics of living free-radical polymerization of styrene in the presence of alkoxyamine: Interpretation within the framework of secondary inhibition hypothesis

The kinetics of the free-radical polymerization of styrene at 120°C in the presence of alkoxyamine as a living polymerization agent has been studied. The alkoxyamine forms in situ with a 100-fold variation in the initial concentration of 2,2,6,6-tetramethyl-1-piperidinyloxy. The rate of the process at the stationary stage decreases with an increase in the initial concentration of 2,2,6,6-tetramethyl-1-piperidinyloxy. The computer simulation of the kinetic features of the process under study demonstrates that this tendency is related to the possible secondary inhibition of the process by alkoxyamine and/or hydroxylamine arising in the system in the course of polymerization.

Modification of epoxy polymers with small additives of multiwall carbon nanotubes

The effect of small additives of functionalized multiwall carbon nanotubes used as a modifier on the formation and properties of epoxy polymers cured with diaminodiphenyl sulfone is investigated. In the range of additive concentrations 0.01–0.50 wt %, there are extreme dependences of dynamic storage modulus and the glass-transition temperature on modifier concentration. As shown by electron microscopy and X-ray scattering, regions with increased packing densities of macromolecules are formed in the polymers in the presence of the modifier. The effect of the specific surface on the kinetics of curing of epoxy resins is observed. A mechanism controlling the formation of the epoxy matrix that is responsible for the inhomogeneous polymer structuring that defines the final properties of the polymers is suggested.

Synthesis and properties of polyvinylpyrrolidone films containing the photomagnetic chromium (tris)oxalate complex

Uniform composites of polyvinylpyrrolidone with the paramagnetic chromium (tris)oxalate complex (C23H23N2O+)3Cr(C2O4)3·11.56 H2O and cation of quinoline spiropyran of the indo-line series were obtained for the first time. Their photochemical properties and static and superhigh-frequency dynamic magnetic characteristics were studied. The change in the ESR spectra under UV irradiation in films of polyvinylpyrrolidone containing photochromic paramagnetic was observed.

Spectral and kinetic characteristics of formyl-substituted spiropyran in poly(methyl methacrylate) modified with elastomers

The efficiency of photochemical transformations of 1′,3′,3′-trimethyl-6′-formyl-8′-allylspiro[2H-1-benzopyran-2,2′-indoline] in PMMA modified with small amounts of poly(ethyl acrylates) of different structures is studied. It is shown that, in the presence of these additives, the quantum yield of the coloring reaction of the photochromic compound under UV irradiation and the rates of photochemical reactions (forward and back) increase. The maximum efficiency of photochemical parameters is observed for PMMA containing small amounts of linear poly(ethyl acrylate) occurring as a microphase in a glassy matrix.

Rate constants of substantial initiation in free-radical polymerization: A new method for determination of conversion dependences

A new method for determination of the conversion dependence of substantial initiation rate constants k i = f(C) in free-radical polymerization processes has been developed. On the basis of the known data on k i1 = f(C) dependences for initiator I1 and the kinetic analysis of a single trivial and simple experiment, this method allows one to calculate k i2 = f(C) function for any other initiator I2 under the same conditions (monomer, temperature). The reference experiment includes measurements of polymerization rates in the presence of initiator I1 in a wide conversion range from 0 to 100% and in the presence of I2, on the condition that the rates of initiation are equal w i1 = w i2, thus ensuring equal initial rates of polymerization. The above-described approach has been approved for the polymerization of styrene, methyl methacrylate, and vinyl acetate initiated with AIBN and benzoyl peroxide.

Modification of polymer surfaces based on polyurethanes with photochromic compounds

The possibility of covalent fixing of hydroxyl-containing photochromic compounds on the surface of polyurethane films containing excess isocyanate groups was studied. By comparing the spectral-kinetic characteristics of polyurethane films treated with solutions and films with chromene or spirooxazine derivatives introduced into the bulk polymer, it was concluded that in the first case the polymer swells and the photochromic compound becomes distributed predominantly in the bulk polymer rather than on the surface.