Pseudoliving polymerization of vinyl acetate mediated by reversible addition-fragmentation chain-transfer agents

The homopolymerization of vinyl acetate mediated by dithiobenzoates and trithiocarbonates as reversible addition-fragmentation chain-transfer agents is studied. The polymerization of vinyl acetate is characterized by some distinct features: (i) a substantial role of chain-termination reactions involving radical intermediates in the kinetics of the process that increases as the concentrations of the reversible additionfragmentation chain-transfer agent and the initiator increase and as temperature decreases and (ii) the occurrence of side reactions of chain transfer to monomers and polymers. The role of these reactions significantly increases with conversion of the monomer. Thus, in order to prepare a narrowly dispersed PVA via the reversible addition-fragmentation chain-transfer mechanism, the process should be conducted to small conversions (15–20%) at moderately high temperatures (80°C) and at a small molar excess of the reversible addition-fragmentation chain-transfer agent with respect to the initiator. A technique for the synthesis of block copolymers based on PVA and poly(n-butyl acrylate) via the reversible addition-fragmentation chain-transfer mechanism is developed.     

Sorption of anionic amphiphilic block copolymers by a network polycation

The interaction of amphiphilic block copolymers comprising an anionic block (polyacrylate or polymethacrylate) and a hydrophobic block (polystyrene, poly(butyl acrylate) or polyisobutylene) with lightly crosslinked poly(N,N-diallyl-N,N-dimethylammonium chloride) is studied for the first time. It is shown that the cationic hydrogel can sorb anionic amphiphilic block copolymers via electrostatic interaction with the corona of block copolymer micelles. The rate of sorption of block copolymer polyelectrolytes is significantly lower than the rate of sorption of linear polyions and is controlled by the lengths of the hydrophilic and hydrophobic blocks and the flexibility of the latter blocks. The sorption of amphiphilic block copolymers is accompanied by their self-assembly in the polycomplex gel and formation of a continuous hydrophobic layer impermeable to water and the low-molecular-mass salt dissolved in it.     

On the Asymptotics of Solutions of the Second-Order Differential Equations with Rapidly Varying Nonlinearities

Ukrainian Mathematical Journal - We establish new results concerning the conditions of existence of one class of monotonic solutions of a two-term nonautonomous differential equation of the second...     

Steady-State Heat Distribution in Bimaterial with an Interface Crack: Part 2

Computational Mathematics and Mathematical Physics - The problem of a steady-state heat distribution in a domain consisting of two subdomains filled with different inhomogeneous materials is...     

On the Asymptotics of Solutions of Second-Order Differential Equations with Rapidly Varying Nonlinearities

Ukrainian Mathematical Journal - We establish conditions for the existence of one class of monotone solutions of two-term nonautonomous differential equations of the second order with rapidly...     

Two-Dimensional and Screw Growth of MoS2 Films in the Process of Chemical Deposition from the Gas Phase

Russian Journal of Applied Chemistry - The method of deposition from the gas phase is applied to the synthesis of thin films of molybdenum disulfide. It was established that varying the rate of...     

Thermal transformations of gamma alumina with phosphorus oxide surface nanostructures

Differential scanning calorimetry, thermogravimetry, and X-ray diffraction analysis were used to study the fundamental aspects of structural-chemical transformations occurring under the action of temperature in the range 50–1530°C in the system constituted by alumina core and phosphorus oxide shell synthesized by the molecular-layering method. It was shown that, as the P/Al molar ratio in the system increases from 0.05 to 0.14, the stability range of low-temperature forms of alumina extends to higher temperatures because crystalline aluminum phosphate is formed on the surface. It was demonstrated that using an inorganic binder based on a silicate binding agent and alumina modified with an aluminum phosphate layer provides a ~3.5-fold increase in the mechanical strength of the material at a ~5-fold decrease in the internal stress as compared with the composition with the unmodified oxide.     

New statistical data on the topology of homomolecular organic crystals

M. V. Lomonosov State University, Moscow. L. Ya. Karpov Scientific-Research Physicochemical Institute. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 4, pp. 148–153, July–August, 1990.