D. I. Kalugin

Gradient Copolymers: Synthesis, Structure, and Properties

Conditions of formation of gradient copolymers characterized by a continuous change in composition along each chain and methods of their synthesis by living ionic and pseudoliving radical polymerizations are considered. Characteristics, structure, and physicochemical properties of gradient copolymers are discussed.

Radical Polymerization of N -Vinylcaprolactam in Benzene Solutions in a Wide Conversion Range

The kinetics of radical polymerization of N-vinylcaprolactam initiated by the thermal decomposition of AIBN at 60°C in monomer solutions in benzene has been studied in a wide range of conversions. The heat of polymerization of N-vinylcaprolactam is 76.0 ± 0.9 kJ/mol; at initial conversions, the polymerization of N-vinylcaprolactam is of the first order with respect to the monomer and of the 0.5th order with respect to the initiator. The ratio of chain propagation and chain termination rate constants kp/kter0.5 is 0.578 l0.5/(mol s)0.5, thus suggesting a high propagation rate constant kp > 103 l/(mol s). At a high initial concentration of the monomer, the kinetic curves demonstrate a weakly pronounced gel effect, and, in the gel permeation chromatography curves of the polymers, the second high-molecular-mass mode emerges, whose intensity grows with conversion. The observed kinetic features are interpreted in terms of the diffusion control of the gel effect.

Synthesis of gradient copolymers of styrene and tert-butyl acrylate by pseudoliving radical polymerization mediated by the reversible inhibitor TEMPO

The gradient copolymers of styrene and tert-butyl acrylate are synthesized by pseudoliving free-radical polymerization in the presence of TEMPO. Despite the inability of tert-butyl acrylate to undergo polymerization in the presence of the nitroxide TEMPO, the introduction of styrene makes it possible to perform the process under the controlled reversible-inhibition regime. The introduction of an additional high-temperature initiator, cumene hydroperoxide, increases the yield of the copolymer, while the pseudoliving mechanism of the process is preserved. This phenomenon is confirmed by the facts that the concentration of nitroxide remains almost invariable during polymerization and that the molecular mass of the polymerization product increases with conversion. Variations in the composition of the copolymer and its molecular mass during polymerization are evidence that the gradient copolymers are formed.

Coal Tar Pitch Modification Methods: Effect of Surfactant Substances and Carbon Additives on Binder Properties

The effect of modifying coal tar pitch with different additives is studied; surfactant substances (SAS), carbon-containing modifiers, and high-temperature binder additives. Using SAS a reduction is observed in viscosity for a system of original pitch–modifier, and with a concentration of 7 wt.% it is most effective to use oleic acid, but with a concentration of 10 wt.% to use myristic acid. In both cases viscosity is reduced by almost a factor of ten with respect to original pitch viscosity. In the case of carbon-containing additives viscosity increases, the same as with use of a high-temperature binder. The effect of modifiers on coke residue yield is studied. On modifying pitch with SAS the reduction in coke residue obeys an additivity rule, which is explained by total removal of SAS from a pitch–modifier system. With use of carbon-containing modifiers and high-temperature binder the coke residue also increases by an additive rule.

Experimental and theoretical determination of Young’s modulus for a composite material made of phenolic resins reinforced by short fibers

The elastic moduli of a composite material made of high-temperature modified phenolic resins with short carbon fibers are studied. Several analytical formulas used to determine the effective moduli of such composites are compared and experimentally verified.