Synthesis of Vinyl-Containing Polydimethylsiloxane in An Active Medium.

This research deals with the synthesis of copoly(methylvinyl)(dimethyl)siloxanes by the copolycondensation of dimethyldiethoxy- and methylvinyldimethoxysilane in an active medium, followed by thermal condensation in a vacuum. We achieved a range of copolymers exhibiting finely tuned molecular weights spanning between 1500 and 20,000 with regulated functional methylvinylsiloxane units. Analysis of the microstructure showed that the copolymerization predominantly formed products demonstrating a random distribution of units (R~1). However, an increase in the content of vinyl-containing monomers increases the R parameter, indicating an enhanced tendency towards alternating linkages within the copolymer matrix.

Multiarm Star-Shaped Polydimethylsiloxanes with a Dendritic Branching Center.

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.

Synthesis of 1,1,3,3,5,5-Hexamethyl-7,7-diorganocyclotetrasiloxanes and Its Copolymers.

This paper reports a method for the synthesis of 1,1,3,3,5,5-hexamethyl-7,7-diorganocyclotetrasiloxanes by the interaction of 1,5-disodiumoxyhexamethylsiloxane with dichlorodiorganosilanes such as methyl-, methylvinyl-, methylphenyl-, diphenyl- and diethyl dichlorosilanes. Depending on the reaction conditions, the preparative yield of the target cyclotetrasiloxanes is 55-75%. Along with mixed cyclotetrasiloxanes, the proposed method leads to the formation of polymers with regular alternation of diorganosylil and dimethylsylil units. For example, in the case of dichlorodiethylsilane, 70% content of linear poly(diethyl)dimethylsiloxanes with regular alternation of units can be achieved in the reaction product. Using 7,7-diethyl-1,1,3,3,5,5-hexamethylcyclotetrasiloxane as an example, the prospects of the mixed cycle in copolymer preparation in comparison with the copolymerization of octamethyl- and octaethylcyclotetrasiloxanes are shown.

Solvent-free synthesis and characterization of allyl chitosan derivatives.

The solvent-free synthesis of allyl-substituted chitosan derivatives through reactive co-extrusion of chitosan powder with allyl bromide at shear deformation was performed. For the structural characterization, FTIR and NMR methods were employed. The results were confirmed by chemical analysis. The total content of allyl substituents from 5 to 50 per 100 chitosan units as a function of the component ratio in the reactive mixtures was revealed. Carrying out the reaction without any additives leads to the selective formation of N-alkylated derivatives, whereas in the presence of alkali the ethers of chitosan were preferentially formed. The results suggest that the proposed approach allows significantly higher yield of products to be obtained at high process speeds and significantly lower reagent consumption as compared with the liquid-phase synthesis in organic medium. The synthesized unsaturated derivatives are promising photosensitive components for use in laser stereolithography for fabrication of three-dimensional biocompatible structures with well-defined architectonics.