N. G. Vasilenko

Preparation of multi-arm star polymers with polylithiated carbosilane dendrimers†

Polyfunctional dendrimers are employed for the synthesis of multi-arm star-shaped polymers. Terminal allyl groups of a carbosilane dendrimer have been partly extended by hydrosilylation-addition of didecylmethylsilane and partly lithiated by reaction with butyllithium. Due to the peculiar structure of the dendritic polylithium compounds, the carbanionic sites were screened from intermolecular interaction and did not aggregate. Good solubility and accessibility for different monomers allowed the preparation of new star-branched poly(dimethylsiloxane), polystyrene and poly(ethylene oxide) polymers.

Polycondensation of alkoxysilanes in an active medium as a versatile method for the preparation of polyorganosiloxanes

Hydrolytic polycondensation of functional derivatives of silicon is an important method for preparation of polysiloxanes of different structure ranging from organocyclosiloxanes to high-molecular-weight linear, cyclolinear, or branched polymers. The most widely used version of hydrolytic polycondensation is based on the use of organochlorosilanes. More than a five decade history of the industrial use of this process resulted in a broad range of organosilicon compounds without which modern technology cannot even be imagined [1]. However, until now, it was impossible to solve two fundamental problems, namely, eliminate the use of chlorosilanes in polysiloxane preparation processes and carry out hydrolytic polycondensation under homogeneous conditions. The significance of the first issue is obvious in view of the need to decrease the environmental pressure. Currently, the use of alkoxy derivatives instead of organochlorosilanes is held up not only by the lack of industrial direct synthesis of organoalkoxysilanes but also by the difficulty to control the polymer production processes from these raw materials. The solution of the latter problem would markedly increase the process controllability, most of all, through control of the product structures. A study of the reaction of organoalkoxysilanes with an excess of anhydrous acetic acid has shown that the process can be accompanied by complete conversion of alkoxysilyl groups within polyfunctional oligomers or their mixtures with alkoxysilanes. Acetic acid was used as the active reaction medium. A fundamental difference between the active medium and common organic solvents is that the former does not merely dissolve the reactants and products but is also a coreactant. Analysis of the literature concerning this pair of reactants has shown that acetic acid either functioned as an active solvent [2‐4] (in this case, water was added to the reaction mixture for hydrolysis) or as a reactant [5] (in this case, complete conversion of alkoxysilyl groups could not be attained). The authors were the first to demonstrate that an excess of anhydrous acetic acid induces the process to follow the hydrolytic polycondensation mechanism, the required water being generated in the reaction system in amounts needed for complete conversion of the alkoxysilyl groups. The key studies were performed for the reaction of acetic acid with dimethyldimethoxysilane. For the convenience of monitoring the reaction, it was carried out in deuterated acetic acid ( CD 3 COOD ). In this case, the variation of the reactant concentrations could be monitored by recording the 1 H NMR spectra of samples taken directly from the reaction mixture without any additional treatment. The signals for different methoxygroup protons (Fig. 1) were assigned on the basis of preliminary experiments including measuring the individual spectra of the major components of the reaction mixture. The absence of acetic acid protons in the spectrum made it possible to calculate the relative concentrations of functional groups in the reactants and products from the intensities I of the proton signals of these groups in the methoxy region (3.3‐3.7 ppm). In view of the fact that the sum of integral intensities in this region ( Σ I ) remains constant during the reaction, the relative concentrations of functional groups ( c rel ) in this spectral region were calculated using the formula c rel = I / Σ I .

Hydrolytic polycondensation of sodiumoxymethyl(dialkoxy)silanes as a method for producing linear poly[(sodiumoxy)methylsilsesquioxane]

Polyfunctional linear poly[(sodiumoxy)methylsilsesquioxanes] are obtained via the hydrolytic polycondensation of sodiumoxymethyl(dialkoxy)silanes. Blocking of sodiumoxy groups with vinyl(dimethyl)chlorosilane is employed to obtain vinyl(dimethyl)siloxane replicas of polyfunctional matrices. The linear structure of the polymers is studied by GPC, NMR spectroscopy, and elemental analysis. The specific properties of poly[vinyl(dimethylsiloxy)methylsilsesquioxane] are investigated and are shown to be primarily related to an abnormally dense organization of polymer coils in solutions.

Synthesis of diethoxy(phenyl)silane and its polycondensation in acetic acid

Low-temperature reaction between phenylmagnesium chloride and triethoxysilane at lowered affords diethoxy(phenyl)silane, whose polycondensation in acetic acid gives oligomeric (phenyl)hydrosiloxanes.

Synthesis and properties of carbosilane dendrimers of the third and sixth generations with the ethylene oxide surface layer in bulk and in monolayers at the air-water interface

A number of carbosilane dendrimers with the ethylene oxide surface layer was synthesized. The density of the surface layer determines their capability to form a physical network due to intermolecular entanglements. The specific interactions of the ethylene oxide fragments exert a minor effect on the thermal behavior of dendritic macromolecules. The compression-expansion isotherms of Langmuir films together with Brewster angle microscopy data show that an increase in the core rigidity with increasing the generation number favors the formation of ordered molecular multilayers. The appearance of a pronounced hysteresis in the compression-expansion cycles is a common phenomenon for amphiphilic dendrimers of high generations.

Synthesis of dimethylcyclosiloxanes in the active medium

The process of condensation of dimethyldiethoxysilane in the active medium in a presence of acetyl chloride, trifluoroacetic acid, and sulfocationites has been investigated. Their impact on the rate and selectivity of the process has been estimated. The prospects of the application of sulfocationites for the polycondensation of dimethyldiethoxysilane in anhydrous acetic acid with an 99% yield have been demonstrated.

Comb-Like Polymethylsiloxanes. Synthesis, Structure and Properties

Comb-like polymethylsiloxanes consisting of a silsesquioxane backbone and dimethylsiloxane side chains were synthesized by means of the “grafting to” method using a linear polyfunctional matrix [SiMe(ONa)O]n and monofunctional oligomers (CH3)3Si[OSi(CH 3)2]nOCOCH3. The effects of architecture of the synthesized methylsiloxane polymers on their physicochemical properties, rheology, and behavior at the air–water interface were studied and compared with those for the linear analogue – polydimethylsiloxane.

Synthesis of alkoxybenzylmethylsilanes and polybenzylmethylsiloxane polymers on their basis

An efficient solvent-free procedure for the preparation of alkoxybenzylmethylsilanes by organomagnesium synthesis was developed. The reaction conditions gave the high yields of the target products. A number of benzylmethylsiloxane polymers was synthesized by polycondensation of alkoxybenzylmethylsilanes in anhydrous acetic acid. The products obtained can become a good alternative to phenylsiloxanes in some practical applications.

Synthesis and Gas-Transport Properties of Iron- and Zirconium-Containing Polydimethylsiloxanes

Novel membrane materials—three-dimensional polydimethylsiloxane networks with nonaggregated metal atoms (Fe, Zr)—have been synthesized using commercial siloxane rubber SKTN and polyfunctional metallosiloxane as a crosslinking agent. For the resulting composites, the permeability, diffusion, and solubility coefficients for a wide range of gases have been determined. It has been found that the permeability coefficients for most of the gases are close to values previously obtained for linear siloxanes; however, the permeability and Р(С4Н10)/Р(СН4) selectivity for n-butane are significantly higher. It has been shown that the differences in the permeability coefficients are attributed to higher solubility coefficients of gases in the synthesized composites.

Synthesis and Properties of MQ Copolymers: Current State of Knowledge

In this review, we discuss currently available studies on the synthesis and properties of MQ copolymers. The data on methods of producing hydrolytic and heterofunctional polycondensation of functional organosilanes as well as the obtaining MQ copolymers based on silicic acids and nature silicates are considered. The ratio of M and Q monomers and the production method determine the structure of MQ copolymers and, accordingly, their physicochemical characteristics. It is shown that the most successful synthetic approach is a polycondensation of organoalkoxysilanes in the medium of anhydrous acetic acid, which reduces the differences in reactivity of M and Q monomers and leads to obtaining a product with uniform composition in all fractions, with full absence of residual alkoxy-groups. The current concept of MQ copolymers is that of organo-inorganic hybrid systems with nanosized crosslinked inorganic regions limited by triorganosilyl groups and containing residual hydroxyl groups. The systems can be considered as a peculiar molecular composites consisting of separate parts that play the role of a polymer matrix, a plasticizer, and a nanosized filler.