Application of size exclusion chromatography to the structural study of polyorganometallosiloxanes

Size exclusion chromatography was employed to elucidate the structure of the organosiloxane moiety in trimethylsiloxy derivatives of organometallosiloxanes containing Na, K, Ni, Mn, Cu, and Fe. An efficient technique of trimethylsilylation of organometallosiloxanes was developed to minimize alterations in their structure. The TMS derivatives of organometallosiloxanes were found to exist mostly as a more or less polydisperse mixture of cyclic poly[phenyltrimethylsiloxy siloxane]s. The preferred size of the cycles depends primarily on the nature of the metal in organometallosiloxane.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1057–1062, June, 1994.This work was performed with the financial support of the Russian Foundation for Basic Research (Grant No. 93-03-18121).     

Effect of synthesis conditions on the mechanism of reversible inhibition in the TEMPO-mediated polymerization of 4-vinylpyridine

The effects of polymerization conditions (the types and concentrations of initiator and solvent, the TEMPO-to-initiator molar ratio, and temperature) on the kinetics and mechanism of pseudoliving radical polymerization of 4-vinylpyridine mediated by the nitroxide TEMPO are studied. The key quantitative parameters of the process are calculated: namely, the rate constant of reinitiation, the rate constant of inhibition, and the product of the propagation-rate constant and the pseudoliving equilibrium constant. The optimum conditions for the controlled synthesis of poly(4-vinylpyridine) mediated by TEMPO are ascertained.     

Simultaneous multiple capture in a simple pursuit problem

The necessary and sufficient conditions for simultaneous multiple capture in a simple group pursuit problem with different opportunities for the participants are obtained.     

Synthesis and molecular-mass characteristics of some cardo poly(benzimidazoles)

The GPC procedure for analyzing molecular mass characteristics of cardo poly(benzimidazoles) has been developed. In most cases, the reaction between 4,4′-oxydibenzene-1,2-diamine and 4,4′-(3-oxo-1,3-dihydroisobenzofuran-1,1-diyl)dibenzoic acid in Eaton’s reagent is accompanied by formation of a microgel. Depending on the synthesis conditions (temperature, duration of heating, and content of phosphorus pentoxide in the reaction mixture), polymers with both unimodal and bimodal molecular mass distributions can be prepared. Formation of the microgel fraction is observed for many representatives of poly(benzimidazoles) of various chemical structures. Based on the experimental evidence, the most probable pathway is suggested for the branching side reaction of poly(benzimidazoles) during their synthesis in Eaton’s reagent.     

Local mobility and rheological characteristics of gels based on hydrophobically modified poly(acrylamides)

For hydrophobically modified poly(acryl amide), we analyze the effect of various parameters of the macromolecular structure (number and length of side hydrophobic groups, content of charged groups, type of bonding between side chains and the polymer backbone, and the degree of blocking of hydrophobic groups distributed along the chain) on the local mobility of physical network junctions and rheological characteristics of gels. We have found that the local mobility measured by the method of spin-probe EPR spectroscopy is either independent or it slightly depends on the above parameters. At the same time, these parameters exert a strong effect on the rheological characteristics of gels. This disagreement can be explained by the fact that local mobility of junctions is primarily controlled by the intermolecular interactions of hydrophobic groups and by the covalent bonding between these groups and a macromolecule. However, the rheological characteristics depend on the number of junctions, their dimensions, and other parameters.     

New Approach to the Synthesis of Polyacrylamide in Miniemulsified Systems

Summary: A new approach to the preparation of water soluble polymer in inverse miniemulsions is proposed. A redox initiation system consisting of ceric ions and carbohydrate‐based surfactant Span 60 as a reducing agent is successfully used for the polymerization of AAm. This initiation system provides chain nucleation and growth near interfacial boundaries. As a result, stable uniform latex with particle radius of about 50–70 nm is obtained. The prepared PAAm has a rather high of up to about 2 × 10⁶ Da.

     

New polymers and copolymers based on 1-trifluoromethyl-1-ferrocenyl-2,2,2-trifluoroethyl methacrylate

Carbon-chain ferrocene-fluoro-containing (co)polymers are synthesized by the free-radical polymerization of 1-trifluoromethyl-1-ferrocenyl-2,2,2-trifluoroethyl methacrylate and its copolymerization with methyl methacrylate in organic solvents and supercritical carbon dioxide. The structures, solubilities, molecular masses, and thermal characteristics of these (co)polymers are studied. It is found that the introduction of 1–5 mol % of the ferrocene-fluoro-containing monomer in the chain of poly(methyl methacrylate) improves its thermal resistance and thermo-oxidative stability.