Reaction for the preparation of unique cyclic polysiloxanes with large size and narrow distribution

Utilizing collective forces between reactant and multiple catalyst molecules has been unprecedented due to the difficulty in realizing high order catalysis. Inspired by the power of collective forces in enzymes and organic catalysts, herein we report a rare example of high order catalysis for ring opening reaction (ROR) of strained rings by methanol. ROR is an important way to produce various polysiloxanes, but usually suffers from serious side reactions especially at high conversion, and currently there is a need to design new reaction pathway to achieve low molecular dispersity. In our study, the judiciously designed strained spiral cyclosiloxanes enable a high order catalysis by methanol, and this new methodology leads to a cyclic polysiloxane with high molecular weight and low dispersity even at full conversion of reactants. Kinetic study indicates an extremely unusual high-order reaction involving multiple methanol molecules per reaction, also confirmed by quantum calculation which reveals the presence of zwitterionic ions stabilized by collecting force of hydrogen bonds by methanol molecules. The inherent driving force for this unusual phenomenon is dominated by enthalpy stabilization of the reactive intermediates through hydrogen bonding. The selective formation of Si O Si bonds, instead of silanol products, reflects the power of scientific design.     

The Synthesis of Fluorine Containing Polysiloxanes. Part 1. The Synthesis of Fluorine Containing Cyclosiloxanes

A new facile preparative method for the synthesis of semifluorinated organocyclosiloxanes is reported. Ring closure of the dichlorosilanes with NaHCO₃ and pyridine gave a mixture of semifluorinated organocyclosiloxanes with cyclotrisiloxane as the main product in yields 95–98% with yield of cyclotrisiloxanes up to 80%.     

正交试验法水解合成乙烯基硅烷混合环体

采用L9(3^4)正交试验法，研究了影响混合单体水解合成乙烯基环体的因素，通过对试验结果的分析找出水解合成乙烯基混合环体的最佳条件。     

Synthesis of microsequential methylvinylsiloxane–dimethylsiloxane copolymers by nonequilibrium copolymerization

Nonequilibrium anionic ring-opening copolymerization of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane (V₄) with hexamethylcyclotrisiloxane (D₃) was examined as a route to methylvinyl–dimethylsiloxane microsequential copolymers. The copolymerization was carried out in toluene and was initiated with Me₃SiCH₂Li using DMSO as the promoter. Distribution of siloxane units obtained from kinetic analysis based on first-order Markovian statistics was compared with that found from analysis by ²⁹Si NMR spectroscopy. Results showed that although chain transfer and back-biting play some role in this system, the kinetics of copolymerization may be described to a reasonable approximation by the first-order Markov model. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 137–145, 1998     

The Synthesis of Methyl-(β-cyanoethyl)cyclosiloxanes

A series of methyl-( g -cyanoethyl) cyclotri-, tetra-, and pentasiloxanes has been prepared using oxygen-halogen exchange between silicon and tin in the reaction of f , y -dichloro(methyl- g -cyanoethyl)oligosiloxanes with bis-tri-n-butylstannyloxy-diorganosilanes.     

1,2-Dimethyl-1,2-diphenyidisilane-1,2-diol and its K,Na, and FeII derivatives. Molecular structure of the all-trans-isomer, 2,3,5,6-tetra-methyl-2,3,5,6-tetraphenyl-1,4-dioxa-2,3,5,6-tetrasilacyclohexane

Hydrolysis of 1,2-dimethyl-1,2-diphenyl-1,2-dichlorodisilane yields 1,2-dimethyl-1,2diphenyldisilane-1,2-diol, which undergoes dimerization into stereoisomeric 2,3,5,6-tetramethyl-2,3,5,6-tetraphenyl-1,4-dioxa-2,3,5,6-tetrasilacyclohexanes under the action of H₂SO₄. Pure all-trans-isomer has been isolated and characterized by¹H NMR and IR spectroscopy and X-ray analysis. The reaction of sodium disilanediolate with FeBr₂ results in the formation of 1,2-dimethyl-1,2-diphenyl-4-ferra(ii)-3,5-dioxa-1,2-disilacyclopentane.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2550–2556, October, 1996.     

Synthesis of methylcyclotetra(hexa)siloxanes with different reactive groups at the same silicon atom

Representatives of methylcyclotetra(hexa)siloxanes with two different reactive groups at the same silicon atom (CH₂=CH and Cl, H and Cl, CH₂=CH and OH) were synthesized for the first time by condensation of trichlorovinylsilane with dihydroxydimethylsilane, and by stepwise condensation of trichloro-and trichlorovinylsilane with 1,3-dihydroxy-1,1,3,3-tetramethyldisiloxane in the presence of amines (aniline, pyridine, and triethylamine). The condensation with 1,3-dihydroxy-1,1,3,3-tetramethyldisiloxane with a large excess of trichlorosilane, unlike the condensation with trichlorovinylsilane, occured intramolecularly to give monochlorotetramethylcyclotrisiloxane in a high yield and intermolecularly to give 1,1,7,7-tetrachloro-3,3,5,5-tetramethyl-1,7-dihydrotetrasiloxane. The structures of the synthesized compounds were confirmed by ¹H and ²⁹Si NMR spectroscopy, IR spectroscopy, and mass spectrometry. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 932–936, June, 2006.     

Copper/sodium-directed hydrolytic condensation of methyltriethoxysilane: Self-assembly of polyhedral Cu/Na-methylsiloxane. Synthesis and properties of new stereoregular macrocyclosiloxane

A hydrolytic condensation of methyltriethoxysilane was performed in the presence of sodium and copper ions. A crystalline copper/sodium-methylsiloxane of a general formula {Na₄[(MeSi(O)O)₁₂Cu₄]} · 6(n-BuOH) (1a) was obtained as the only product in a high yield. X-ray analysis of a single crystal obtained after recrystallization of 1a by slow diffusion of methanol vapours into its ethanol solution was characterised as {Na₄[(MeSi(O)O)₁₂Cu₄]} · 4(MeOH) · 4(EtOH) (1b). In the crystal molecules are assembled into zig-zag chains by O-H?O bonds. Removal of metal ions by a reaction of 1a or 1b with Me₃SiCl gave a new siloxane macrocycle tris-cis-tris-trans-dodecamethyldodecatrimethylsiloxycyclododecasiloxane, [MeSi(O)OSiMe₃]₁₂ (2), in a high yield.     

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.