Yu. D. Semchikov

Controlled radical copolymerization of N-vinylpyrrolidone with 1,1,1,3,3,3-hexafluoroisopropyl-α-fluoroacrylate

Narrow disperse copolymers of N-vinylpyrrolidone with 1,1,1,3,3,3-hexafluoroisopropyl-α-fluoroacrylate have been prepared for the first time by reversible addition fragmentation chain transfer pseudo-living radical polymerization in the presence of benzyl dithiobenzoate. The relative activities of the monomers indicating the occurrence of alternating copolymerization have been estimated. The copolymerization of equimolar N-vinylpyrrolidone-1,1,1,3,3,3-hexafluoroisopropyl-α-fluoroacrylate mixtures shows typical features of reversible addition fragmentation chain transfer pseudoliving radical polymerization: deceleration of polymerization compared to the classical radical process, degeneration of the gel effect, successive increase in the number-average molecular mass with conversion, and formation of narrow disperse copolymers.

Classical and pseudoliving radical copolymerization of vinyl acetate and acrylic acid in methanol

The homogeneous free-radical copolymerization of vinyl acetate and acrylic acid is studied at 50 and 70°C in methanol with and without the reversible addition-fragmentation chain-transfer agent benzyl dithiobenzoate. It is shown that, under conditions of reversible addition-fragmentation chain-transfer copolymerization, the limiting conversion is 32% and the number-average molecular mass increases linearly with conversion. At the same time, in the absence of the reversible addition-fragmentation reversible chain-transfer agent, the conversion of the monomers amounts to 63% and the molecular mass of the copolymers decreases with conversion.

Hydrodynamic and molecular characteristics of graft copolymers of chitosan with acrylamide

The conformational properties of macromolecules of chitosan and its copolymers with acrylamide in a mixed solvent 0.33 M CH3COOH + 0.3 M NaCl have been investigated by means of translation diffusion and viscometry. The copolymer macromolecules in a solvent suppressing polyelectrolyte effects possess a higher intracoil density (ρav = 0.010 g/cm3) than the chitosan macromolecules (ρav = 0.006 g/cm3), even though the hydrodynamic radius R h of chitosan is smaller by a factor of ∼1.5.

Degradation of Chitosan in Solutions in the Presence of a Redox System

The degradation of chitosan in aqueous solutions of acetic and hydrochloric acids initiated by the hydrogen peroxide-ascorbic acid redox system has been studied. The nature of acid strongly affects the degree of degradation and the molecular mass of oligochitosan—the reaction product. The relationship between the molecular mass of oligochitosan and the concentration of acetic acid in the solvent is described by a curve with a minimum. If acetic acid is present in a 5-fold molar excess with respect to chitosan units, the starting solution behaves as a Newtonian liquid. It has been demonstrated that, exactly in this solution, oligochitosan with the minimum amount of units is formed.

Controlled polymerization of methyl methacrylate in the presence of an FeCl3-complexing agent system

The controlled polymerization of methyl methacrylate in DMF with participation of FeCl3 and ligands (acrylamide, 1,1,1,3,3,3-hexamethyldisilazane, citric acid, and sulfosalicylic acid) has been studied. It has been shown for the first time that DMF ensures the polymerization of methyl methacrylate in the controlled mode without any other complexing agents. As temperature increases, the rate of the process and the polydispersity of PMMA increase.

Properties of films, solutions, and gels prepared from sodium carboxymethyl cellulose blends with synthetic polymers

An extremal dependence of the intrinsic viscosity of poly(vinyl alcohol) blends with sodium carboxymethyl cellulose and polyacrylamide on composition has been established. A correlation between the viscosity properties of solutions and mechanical properties of films made of sodium carboxymethyl cellulosepoly(vinyl alcohol) blends is observed that is indicative of the interpolymer interaction in these systems. The obtained regularities can be used to produce high-modulus coordination-crosslinked gels based on these blends.

Methacrylic silicon-containing tercopolymers for chemically amplified resists

Tercopolymers of methyl methacrylate with methacrylic acid and dimethylphenyl (methyldiphenyl)silyl methacrylates are synthesized and investigated as components of chemically amplified resistive formulations with sulfonium and iodonium salts as photoacid generators for UV lithography in the 254-nm range. The surface behavior and the kinetics of dissolution of resistive films in an aqueous solution of tetraethylammonium hydroxide in relation to the concentration of onium salts and the temperatures of postapply and postexposure bakes are studied. The introduction of sulfonium salt into the resistive formulation brings about an increase in the solubility of unexposed films, thereby erasing the difference in dissolution rates of exposed and unexposed areas of a resist and preventing image formation. The iodonium salt plays the role of an inhibitor for dissolution of unexposed films of both copolymers, which makes it possible to obtain a high-contrast positive image in resists.

Effect of cobalt(III) 1-nitroso-2-naphtholate on free-radical polymerization to vinyl monomers

It has been shown that, at 70°C, cobalt(III) 1-nitroso-2-naphtholate inhibits the free-radical polymerization of styrene, methyl methacrylate, butyl methacrylate, and butyl acrylate. The induction period linearly increases with complex concentration. The polymerization of styrene (120°C) carried out in the presence of cobalt(III) 1-nitroso-2-naphtholate shows typical features of pseudoliving polymerization, namely, linear ln[M]0/[M]-time and molecular mass-conversion plots. When the monomers are allowed to stand with a complex (7 × 10−3 mol/l) and an initiator (5 × 10−3 mol/l) for 1 day at 20°C, the ESR signal corresponding to the nitroxide radical appears. In the course of polymerization, the signal disappears, indicating the consecutive transformation of the cobalt(III) 1-nitroso-2-naphtholate radical into the macronitroxide adduct. Polystyrene samples isolated at various conversions initiate the secondary polymerization of styrene and its block copolymerization with methyl methacrylate.

Demonstration of the radical character of the mechanism of the thermal decomposition of polyacrylates

1. Additions of dicumyl peroxide and the tert-butyl ester ofΒ-(triethylsilyl) perpropionic acid accelerate the thermal decomposition of polymethyl methacrylate and polybutyl acrylate. 2. Methane, dimethylphenylcarbinol, and (C2H5)4Si were identified in the decomposition products of polyacrylates in the presence of peroxides, indicating stripping of a hydrogen by the peroxide radicals from the polymer molecules. 3. The data obtained confirm the free radical character of the mechanism of the thermal decomposition of polyacrylates.

Infrared spectra of vinyl compounds and the effects of conjugation involving the π-electrons of the vinyl group

The frequencies of the =CH2 group wagging vibration in CH2=CH-X compounds reflects both the inductive effect of the substituents X, and the effects ofπ, π-, π,p- and (d-p)π-conjugation in which these substituents take part.