New organosiloxanes based on 1-vinyl-2-perfluoroalkoxy-2,3,3-trifluorocyclobutanes

A new method for the synthesis of polyfluorinated compounds, viz., chlorosilanes with 2-perfluoroalkoxy-2,3,3-trifluorocyclobutane substituents containing different numbers of tetrafluoro(ethylene oxide) (CF₂CF₂O) _n units (n = 3–6), was developed. The structures of siloxanes formed by the hydrolysis of these chlorosilanes were studied: the hydrolysis of monochlorosilanes affords disiloxanes and that of dichlorosilanes produces cyclotrisiloxanes, cyclotetrasiloxanes, and cyclic (the number of siloxane units >4) and linear polysiloxanes. Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1215–1217, May, 2005.     

Synthesis and some properties of silanes and siloxanes with 5,5,6,6,7,7,7-heptafluoro-4,4-bis(trifluoromethyl)heptyl substituents

Methods for syntheses of new polyfluorinated compounds, viz., silanes containing substituents CF₃CF₂CF₂C(CF₃)₂(CH₂)₃ (R^F) at the silicon atom and 1,3,5-tris(R^F)-1,3,5-trimethylcyclotrisiloxane that can be used for the synthesis of fluorocontaining oligo- and polysiloxanes of different structure, were developed. The polymerization of cyclotrisiloxane in the presence of 1,3-divinyltetramethyldisiloxane gave linear oligomers, whose chain contain -(R^F)Si(Me)O- units.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2133–2136, October, 2004.     

Redistribution of cyclosiloxanes to favor formation of decamethylcyclopentasiloxane

Efforts to optimize the formation of the cyclic D₅ oligomer (D = Me₂SiO) of polydimethylsiloxane have led to the development of a new class of redistribution catalyst, the silyl perchlorates. Where as previous Lewis and Bronsted acid catalysts have transformed D₃ almost exclusively into D_3n oligomers, use of phenyldimethylsilyl perchlorate as the catalyst gives predominantly D₄, D₅, and other non-D_3n oligomers. This redistribution reaction is particularly useful for obtaining large amounts of the difficulty available D₅. Similar studies of D₄ with variation of solvent and catalyst led to little redistribution. © 1993 John Wiley & Sons, Inc.     

Dimesogenic liquid crystalline organosiloxanes

Liquid crystalline (LC) organosiloxanes with two terminal cyanobiphenylyl groups attached to a linear or cyclic siloxane center through an aliphatic spacer (CH₂) _n with i = 10 were synthesized. The ability of compounds to pass into the LC state was confirmed by thermooptical, X-ray diffraction, and calorimetric measurements. The temperatures and the enthalpies of phase transitions were determined. The types of LC structures and the capability of one compound for polymesomorphism to form the chiral S_mC* phase without a chiral center in the mesogenic group were established. The temperatures and the enthalpies of the reversible phase transitions, crystal S_mC S_mA melt and crystal S_mA melt, for linear and cyclic LC organosiloxanes, respectively, were determined. Models of molecular packing in the S_mA and S_mC* phases were proposed based on X-ray diffraction data. A specific feature of the S_mA phases of new LC organosiloxanes is a negative gradient of the temperature dependence of the interlayer spacing.     

Optically active dimethylsiloxane copolymers with nucleophilic chiral sulfur groups pendant to the polysiloxane chain

Polydimethylsiloxanes with part of the siloxane units bearing an optically active sulfoxide group were synthesized. These copolymers had chiral sulfur centres connected to the siloxane chain by a dimethylene bridge. They were obtained mostly by the kinetically controlled anionic ring-opening polymerization of 1-(2-organothioethyl)1,3,3,5,5-pentamethylcyclotrisiloxanes, followed by stereoselective oxidation of prochiral groups to yield partially enantiomeric sulfoxide groups. Sulfoxides bearing cyclic monomers were also used. Polymers were characterized by spectroscopy and polarimetry. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 879–888, 1997     

Synthetic and natural silica‐aluminates as inorganic acidic catalysts in ring opening polymerization of cyclosiloxanes

Ring opening polymerization (ROP) of hexamethylcyclotrisiloxane (D₃) and octamethylcyclotetrasiloxane (D₄) was promoted by acid‐treated synthetic and natural silica‐aluminates. Silica‐alumina (1:3 Si/Al molar ratio) was obtained using a simple and economic route from precipitation of aluminum sulfate solutions. The material was treated in an acidic medium to improve the content of acid sites and successfully tested as inorganic acidic catalyst for ROP of D₃ or D₄ cyclosiloxanes. Natural bentonite was treated and used in a similar manner. Once the ROP reaction completed, the catalyst was easily removed and it was found that the recovered synthetic silica‐alumina was active in a second ROP reaction. The effect of the concentration and type of catalyst in respect to the molecular weight and polydispersity of polydimethylsiloxanes was analyzed: increasing the amount of silica‐alumina in ROP of D₄ from 0.05 to 0.1 g decreased the average molecular weight (M_n = 13–1.8 kDa) associated with an increase in the polydispersity (2.95 vs. 1.81). Analogous results were found with bentonite. These values suggest that an increase in the catalyst concentration led to a lower M_n, with a more homogeneous molecular chain dimension. Copyright © 2012 John Wiley & Sons, Ltd.