B. G. Zavin

Metalasiloxanes: New structure formation methods and catalytic properties

This article is a review of present-day methods of the formation of the structure of various metalasiloxanes (MS’s). Methods of designing the structure of catalytically active MS’s are discussed. In the description of synthetic methods and catalytic properties, the MS’s are divided into two groups, namely, individual and oligomeric MS’s. The first section of the review is devoted to MS’s with coordinatively unsaturated metal sites and to cagelike MS’s. The methods of formation of MS-based catalytic surfaces are analyzed, and synthetic methods converting these surfaces into ordered inorganic catalytic systems are discussed. The second section of the review presents the methods of synthesis of MS oligomers, the ways of regulating the structure of these compounds, and the use of the MS’s as the basic component of catalytic systems for petrochemical syntheses and halohydrocarbon conversion.

Conformation‐Dependent Sequence Design of HP Copolymers: An Algorithm Based on Sequential Modifications of Monomer Units

We present a new modification of the so-called conformation-dependent sequence design scheme for HP copolymers which was proposed several years ago (H and P refer to the hydrophobic and polar monomer units, respectively). New method models the real chemical experiments more realistically. We performed Monte Carlo computer simulations using the bond-fluctuation model for protein-like copolymers obtained by means of the new “iterative” method and compared the results with those obtained for originally proposed “instantaneous coloring” procedure. Copolymers designed by the “iterative” method are shown to have better-optimized functional properties. The investigation of the influence of sequence preparation conditions has revealed that the statistical properties of designed HP sequences depend rather strongly on the density of the parent homopolymer globule but not on the composition of H and P units.

Nanocomposites of ZnS and poly-(dimethyl)-block-(phenyl)siloxane as a new high-refractive-index polymer media

In the present paper, we describe a new and original method to obtain transparent, siloxane-based composites, with high refractive index (up to 1.68). The method is based on the decomposition of Zn-siloxane, mixed with a poly-(dimethyl)-block-(phenyl)siloxane matrix in different ratios. It was found that after treatment of such mixed metal-containing polymer blend with H2S, the nanoparticles of ZnS are formed, with the size in a 1- to 5-nm range, which allow effective increase of the refractive index of the nanocomposite mixture with poly-(dimethyl)-block-(phenyl)siloxane without loss of film transparency. We succeded to increase the refractive index from 1.54 (pure matrix) up to 1.68 (composite with a ZnS content of 4.6 vol.%). The siloxane-based compositions are optically transparent, which makes it possible to use them as light-emitting diodes or solar cell sealants or adhesives.

Relaxation transitions in dimethylsiloxane-phenylsilsesquioxane block copolymers studied by differential scanning calorimetry☆

Changes in heat capacity, temperatures and widths of transitions, and activation energies were determined for relaxation transitions proceeding in samples of dimethylsiloxane-phenylsilsesquioxane block copolymers differing in the content of the stiff blocks, in molar mass of blocks, and in sample history. A number of anomalous transitions in the dimethylsiloxane blocks were observed, not encountered in the corresponding homopolymer. A general approach is suggested for elucidating and predicting the limits of these anomalies, based on the concept that in linear, flexible-chain polymers the α-transition and the β-transition represent respectively an intermolecular cooperative and a quasi-independent motion of segments with length comparable to that of the Kuhn segment.

Synthesis and study of the structure of cage-like metallosiloxanes with pair combinations of 3d transition and alkaline earth metals

The selective replacement of Na ions in cage-like (Cu,Na) organosiloxanes in reactions with divalent metal halides was studied. The sandwich-like isomer [PhSiO2]6Cu4Na4[PhSiO2]6 forms the corresponding bimetallic complexes [PhSiO2]6Cu4M2[PhSiO2]6 (M = Cu, Zn, Mg, Sr, Ba) retaining a sandwich-like structure (in 60–90% yields) regardless of the metal ion size in MCl2. Under similar conditions, the reactions of the globular isomers [RSiO2]12Cu4Na4 (R = Ph, Me, Vin) with CuX2 (X = Cl or Br) afforded insoluble polymer products. The reaction in dioxane or THF in the presence of DMSO gave the crystalline globular-type metal complexes [RSiO2]12Cu4[CuX]4, in which Na ions are replaced by CuX groups. The compositions and structures of the synthesized metal complexes were studied by X-ray diffraction, elemental analysis, and destructive silylation combined with gel permeation chromatography and 1H NMR spectroscopy.

New cyclolinear permethyloligosilane-siloxanes

Abstract α , ω -Bis(heptamethylcyclotetrasiloxanyloxy)oligodimethylsilanes have been synthesized by heterofunctional condensation of hydroxyheptamethylcyclotetrasiloxane with α , ω -dichloropermethyloligosilanes, Cl(Me 2 Si) n Cl ( n =1–4, or 6). The substances are characterized by mass spectrometry, 29 Si-NMR, IR and UV spectroscopy.

The free-radical mechanism of the SiO bond fracture in polysiloxanes as a result of mechanical disintegration☆

Abstract The structures of the free radicals produced by a mechanical disintegration of cyclic polysiloxanes (polymethyl- and polyphenyl-silsesquioxanes) and of linear structure (polydimethylsiloxane) have been studied by ESR. A free-radical type of siloxane bond fracture is produced by mechanical disintegration.

Oligomerization of organochlorosilanes in the acetylacetone—carbamide system

Condensation of acetylacetone with carbamide in nonpolar media (benzene, toluene) is initiated by organochlorosilanes. The reaction rapidly occurs under mild conditions to give oligosiloxanes and 4,6-dimethylpyrimidin-2(1H)-one hydrochloride. The conversion of chlorosilanes and the yields of oligosiloxanes are nearly ∼100%.

Synthesis of α,ω-dihalopermethyloligosilanes and silane-siloxane copolymers

Abstractα,ω-Dibromopermethyloligosilanes, Br(SiMe2)nBr (n=2–4, 6), were prepared by the reaction of dodecamethylcyclohexasilane with bromine. The reaction of (Me2Si)6 with MCl4 (M=Sn, Ti) proceeds with the cleavage of Si−Si- and Si−C-bonds with the formation of α,ω-dichloropermethyloligosilanes, Cl(SiMe2)nCl (n=2–4, 6), and chloro derivatives of cyclohexasilane, ClmSi6Me12−m (m=1, 2). Silane-siloxane copolymers of regular structure were obtained by heterofunctional copolycondensation of α,ω-dihalopermethyloligosilanes with 1,5-dihydroxyhexamethyltrisiloxane.

The hydrolytic polycondensation of phenyltrichlorosilane with vinyltrichlorosilane

A study was made of the hydrolytic cocondensation of phenyltrichlorosilane (PTCS) with vinyltrichlorosilane (VTCS). It was found that for each type of monomer unit the RSiO(OH)/RSiO1·5 ratio remains constant over the entire range of change in relative PTCS-VTCS concentrations. A feature of the system under review is the marked gelation tendency owing to condensation reactions mainly through OH groups of vinylsiloxane units without multiple bonds of the vinyl groups being affected.