The catalyst-free hydrolytic polycondensation of methyltrimethoxysilane under microwave radiation has been studied. The effect of molar ratios of the reagents (MTMS/H2O = 1/0.5–1/9), radiation power (20–300 W), temperature (30–50 °C) and duration of exposure (2.5–90 min) on the course of the process is considered. It has been shown that the use of microwave radiation promotes the activation of the process, and almost complete conversion of the monomer can be achieved in 5 min at 30 °C, 20 W and an MTMS/H2O ratio of 1/3. The optimal radiation power for the maximum conversion of the monomer and MeO-groups is in the range from 20 to 100 W. An increase in the water amount, the duration and temperature of the process contribute to an increase in the monomer conversion, a decrease in the content of residual MeO-groups and the yield of non-volatile oligomethylsilsesquioxanes. The limits of this approach using to the synthesis of multifunctional branched polyorganosilsesquioxanes are determined. Depending on the process conditions, homogeneous water–alcohol solutions of oligomethylsilsesquioxane with a concentration of 20 to 50 wt.% can be obtained. The OH-group content and the molecular weight of the obtained oligomers vary from 10 to 30 wt.% and from 1000 to 600 Da, respectively.

PDMS telechelics are important both in industry and in academic research. They are used both in the free state and as part of copolymers and cross-linked materials. At present, the most important, practically used, and well-studied method for the preparation of such PDMS is diorganosiloxane ring-opening polymerization (ROP) in the presence of nucleophilic or electrophilic initiators. In our brief review, we reviewed the current advances in the field of obtaining polydiorganosiloxane telechelics and monofunctional PDMS, as well as well-organized branching centers by the ROP mechanism and catalytic rearrangement, one of the first and most important reactions in the polymer chemistry of silicones, which remains so at the present time.

The process of hydrolytic polycondensation of diethoxymethylsilane in water under pressure was investigated without the use of organic solvents in non-catalytic conditions and in carbonic acid. It is demonstrated that in both cases the process of the formation of methylsiloxane polymers proceeds with 100% conversion of the monomer and complete preservation of hydrosilyl groups. The conditions for the selective production of linear products were found.

Dense purely methylsiloxane molecular brushes with high molecular masses were obtained by the 'grafting to' method. Vinyl groups of poly(vinyldimethylsiloxy)methylsiloxane were converted into (chlorodimethylsilyl)ethyl ones whose active chlorine atoms were replaced by monofunctional dimethylsiloxane oligomers having OLi terminal group to arrange side arms of the product. The molecular brushes thus prepared were characterized using physicochemical methods of analysis.

The review is devoted to the analysis of the currently available data in the field of the molecular organization of multiarm stars, macromolecules-particles characterized by the dualism of macromolecular and colloidal properties. Until now, the question of the predominance of polymeric or colloidal behavior for such objects remains open. The distinctive properties of multiarm stars—very low intrinsic viscosity and the formation of monomolecular micelles—are determined by the peculiarities of their molecular organization. The appearance of dendrimers as the initial branching centers made it possible to create a representative number of objects, and this allowed one to study the property–structure relationship for this group of objects at a new qualitative level. The results obtained are important for studying the factors that determine the “anomalous” behavior of macromolecules-particles, such as dendrimers, nanogels, and dense molecular brushes, and provide an important experimental basis for theoretical understanding of the behavior of these objects as a function of their structure.

New non-functional methylsiloxane dendrimers possessing a sparse structure with a trimethylsiloxy outer layer containing a flexible dimethylsiloxane link between branch points have been synthesized. Two alternative synthetic protocols were employed, namely, a divergent scheme comprising an additional stage of generating a spacer –OSiMe2– group with sodium ethoxy(dimethyl)silanolate, and a hybrid method using monofunctional dendrons with a sparse structure.

New multiarm stars have been synthesized based on polylithium derivatives of high-generation carbosilane dendrimers. In the synthesis of multiarm stars based on the eighth-generation dendrimer, steric hindrances were observed even during the synthesis of a polylithium initiator. Subsequently, this led to chain transfer reactions between growing arms, as well as other side effects. As a result, dense nanogel formations with a higher tendency of ordering than in classical objects of this type were isolated from the reaction mixture. The study of the rheology of multiarm stars based on sixth-generation dendrimers made it possible to determine the activation energies of viscous flow in these objects, which makes it possible to consider them as objects with a macromolecular nature and a reptation flow mechanism.

A synthetic process for new functional metallosiloxanes containing M-OEt groups (where M is metal) has been developed. Compounds of iron, aluminum and zirconium were obtained by the interaction of a corresponding metal chloride with a mixture of sodium organoalkoxysilanolate and sodium ethylate in a ratio that makes it possible to preserve and adjust the number of functional groups at the metal atoms. A process of partial hydrolysis of functional metallosiloxanes and a possibility of using the products obtained as a binder in compositions based on silicone rubber have been investigated. It has been shown that such compounds can be used as cross-linking agents in silicone rubber compositions.

The 1,5-disodiumoxyhexamethyltrisiloxane has been isolated in high yield with a purity of up to 98%, by simple interaction of dimethylsiloxanes with sodium hydroxide. The reasons of high selectivity of the reaction towards 1,5-disodiumoxyhexamethyltrisiloxane were analyzed. It was found that variation of reaction time, type of dimethylsiloxane precursor and ratio between sodium hydroxide and dimethylsiloxanes in wide range led to the materialization of most part of used sodium hydroxide in 1,5-disodiumoxyhexamethyltrisiloxane. Its fast crystallization and precipitation from the homogeneous reaction media were found to be the main reason of the high selectivity of the reaction towards 1,5-disodiumoxyhexamethyltrisiloxane. The crystalline structure of 1,5-disodiumoxyhexamethyltrisiloxane was determined and its packaging peculiarities were discussed and illustrated.

Non-functional derivatives of polymethylsilsesquioxane (PMSSQ) dendrimers of first to fourth generation were synthesized for the first time using combination of divergent and convergent synthetic approaches. Obtaining of non-functional derivatives allowed investigating their properties not only in solution, but also in the bulk. While having practically identical chemical composition with linear polydimethylsiloxanes, PMSSQ dendrimers demonstrated increased density, a significant increase in the viscous flow energy, an absence of crystallization, and a gradual increase in the glass transition temperature with the generation.

The rheological measurements of star-shaped polydimethylsiloxanes with 8, 32 and 128 arms synthesized from carbosilane dendrimers of 2nd, 4th and 6th generations, respectively, revealed the Newtonian character of flow in the systems with 8 or 32 arms and a pseudoplastic character of flow in the 128-arm one. The activation energy of viscous flow was found to be 18.5kJmol−1 for all the objects.

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.

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.

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.

New highly functionalized acyclic hyperbranched polyphenylsilsesquioxanes were obtained and transformed into acyclic nonfunctional or cross-linked nanogel particles with specified outer shell.

Hyperbranched polyvinyl- and polymethylethoxysiloxanes were obtained for the first time by heterofunctional polycondensation of the corresponding organoethoxysilanols derived from relevant monosodium organodiethoxysilanolates. Synthesized structures were characterized using 29Si NMR, 1H NMR and infrared spectroscopies, gel permeation chromatography and elemental analysis. On the basis of the obtained hyperbranched polyorganoethoxysiloxanes, new ‘core–shell’ structured polyvinyl- and polymethylsilsesquioxanes with adjustable sizes, different crosslinking densities and variable chemical natures of the core–shell surroundings were prepared, investigated and characterized using 1H NMR and infrared spectroscopies, gel permeation chromatography, thermogravimetric analysis, differential scanning calorimetry and elemental analysis. © 2015 Society of Chemical Industry

Polycondensation of diethoxydimethylsilane (DEDMS) in an active medium containing an excess of acetic acid was studied. It has been shown that the process selectivity could be well managed only if water was generated in the reaction mixture. We have found that both linear oligomers and cyclosiloxanes could be obtained with high selectivity and 80 % yield at least under conditions of the active medium. Further condensation of the linear oligomers led to the formation of α,ω-dihydroxypolydimethylsiloxanes with the molecular weight ranging from 3500 to 70000 Da. The obtained polydimethylsiloxane samples having hydroxyl end groups correspond to the industrial samples of liquid siloxane rubbers in terms of molecular weight parameters and virtually do not contain any low molecular cyclosiloxane impurities.