Conductivities of polysilanes

Measurements of the electrical conductivities of three types of polysilanes were carried out over a range of dc fields and temperatures. These polymers are varied in substituents and structures with formulas of [C₆H₅SiCH₃]_n, [(C₆H₅SiCH₃)₇₀(CH₃SiH)₃₀]_n, and [(C₆H₅SiCH₃)₅₀(C₆H₅SiH)₃₀(CH₃Si)₂₀]_n. Undoped polysilanes behaved as insulators since their conductivities were observed in the range of 10⁻¹⁰ to 10⁻¹³ S cm⁻¹, while SbF₅-doped polysilanes of all kinds behaved as semiconductors with conductivities in the range of 10⁻² to 10⁻⁴ S cm⁻¹. No significant difference in conductivities was observed among three SbF₅-doped polysilanes although these polymers are very different in chemical properties. These experimental results suggest that electrical conductivities of polysilanes are associated with the Si Si main-chain backbone rather than with the side groups. It is evident that the dopant is able to diffuse throughout the bulk of the polymer and the conductivity of the doped polymer is a function of the dopant concentration from the result of in situ monitoring of the resistance of the silane homopolymer during SbF₅ doping at room temperature. The conductivities of polysilanes appeared to be temperature-dependent. The activation energy for the conduction of SbF₅-doped silane copolymer was found to change at its glass transition temperature. © 1996 John Wiley & Sons, Inc.     

Structural characterization and thermal behaviour of block copolymers of polydimethylsiloxane and polyamide having trichlorogermyl pendant groups

Block copolymers having a pendant trichlorogermyl group as a part of polyamide segment? (CO? R′? CO? NH? Ar? NH? )_xCO? R′? CO? and polydimethylsiloxane of general formula [(? CO? R′? CO? HN? Ar? NH)_x? CO? R′? CO? NH(CH₂)₃SiO(CH₃)₂ ((CH₃)₂SiO)_ySi(CH₃)₂(CH₂)₃ NH? ]_n (where R′ = CH₂CH(GeCl₃), CH(CH₃)CH(GeCl₃), CH(GeCl₃)CH(CH₃); Ar = C₆H₄, (? C₆H₃? CH₃)₂, (? C₆H₃? OCH₃)₂, 2,5‐(CH₃)₂? C₆H₂, C₆H₄? O? C₆H₄) were prepared by a polycondensation reaction and characterized using CHN and Ge analysis, Fourier transform infrared (FTIR) and ¹H NMR spectroscopy, thermogravimetric analysis (TGA) and molecular weight determination. They have a lamellar structure with weight‐average molecular weight in the range 1.21 × 10⁵–4.79 × 10⁵ g mol^?1. These copolymers display two glass transition temperatures and have an average decomposition temperature of 489 °C. TGA, FTIR and gas chromatography/mass spectrometry studies indicate that degradation of these block copolymers results in carbon monoxide, oligomeric siloxanes and polyamide fragments. They are thermally stable due to the hydrogen bonded interlinked chains of polyamide, while they absorb water due to the presence of Ge? Cl bonding. Copyright © 2010 Society of Chemical Industry     

Two new siloxanic proton conducting membranes: Part II. Proton conductivity mechanism and NMR study

The synthesis and structural characterization of two types of membranes with formulas {Si(CH₃)₃O[Si(CH₃)HO]_21.26-[Si(CH₃)((CH₂)₃SO₃H)O]_1.8-[Si(CH₃)((CH₂)₃Si(CH₃)₂O-)-O]₁₄-Si(CH₃)₃}_n (A) and {Si(CH₃)₃O[Si(CH₃)HO]_21.26-[Si(CH₃)((CH₂)₃SO₃H)O]_1.8-[Si(CH₃)((CH₂)₃(Si(CH₃)₂O-w₎)-Ov_][Si(CH₃)((CH₂)₃Si(CH₃)₂O-)-O_]14−vSi(CH₃)₃}_n (B), (w=20.31), were previously proposed.The ac electrical response of A and B was fully characterized in the 40 Hz-2 MHz frequency region by studying the impedance spectra in the medium and low frequency regions by equivalent circuits and complex dielectric spectra at high frequency in terms of dielectric relaxation modes. Results demonstrated that A and B conduct ionically by means of a proton exchange event which occurs via a vehicular mechanism between neighboring water clusters formed by water molecules aggregated around each sulfonic acid group of the siloxane side chains. The proton conductivities at 115 °C of ca. 1.9 × 10⁻³ and 1.8 × 10⁻⁴ S cm⁻¹ of fully hydrated membranes A and B, respectively, classify these silicone networks as good proton conductors.Membrane B was chosen for a closer investigation using NMR spectroscopy. Solid state ²⁹Si MAS NMR experiments gave further insight about the three-dimensional structure. Proton diffusion measurements provided some encouraging results about proton dynamics of this membrane signaling the great potential of siloxanic based proton conductors.     

Dendrimeric silanes for formation of metallosilicates: new heterogeneous catalysts for the epoxidation of alkenes with tert-butylhydroperoxide

New metallosilicate catalysts were prepared by reacting a silanol capped dendrimer, Si[CH₂CH₂Si(CH₃)₂OH]₄ with MCp₂Cl₂ (M = Ti^IV, Mo^VI, W^VI and V^V). The resulting Si[CH₂CH₂>Si(CH₃)₂OMCp₂Cl]₄compounds were incorporated in a silica matrix by the sol–gel method. The catalytic activity of the metallosilicates after calcination revealed excellent activity and selectivity towards epoxidation of alkenes with tert-butylhydroperoxide. Maximum activity was observed with molybdenum-containing materials. Analysis of the catalytic activity revealed that the catalysts were truly heterogeneous.     

Some New Mixed-Substituent Phosphazenes Derived from N-Silylphosphoranimines

A series of mixed-substituent P-alkyl-N-silylphosphoranimines, Me₃SiN=P(R)XY (R = n-Pr, n-Bu, i-Pr; X, Y = Br, OCH₂CF₃, OPh), were studied as possible precursors to cyclic and/or polymeric phosphazenes. Three synthetic methods were investigated: sealed-ampule thermolysis, dynamic-vacuum thermolysis, and reactions with CF₃CH₂OH. While the results varied with the specific precursor and reaction conditions employed, these synthetic methods afforded a variety of new non-geminally substituted cyclic trimers, [N=P(R)X]₃ (R = n-Pr, n-Bu, i-Pr; X = Br, OCH₂CF₃, OPh), one new polymer, [N=P(n-Pr)OPh] _n , and a simple route to a known polymer, [N=P(Ph)OCH₂CF₃] _n . The trimers were generally obtained as mixtures of cis and trans isomers although, in one case, [N=P(i-Pr)OPh]₃, the pure trans isomer was isolated and structurally characterized by X-ray diffraction. This paper is dedicated to Professor Harry R. Allcock in honor of his pioneering research and his steadfast leadership in the field of inorganic polymer chemistry.     

Sol–gel formation of heteropolysiloxanes from diethylphosphatoethyltriethoxysilane and tetraethoxysilane

Transparent monolithic gels were prepared from the cohydrolysis of diethylphosphatoethyltriethoxysilane (OC₂H₅)₂P(O)CH₂CH₂Si(OC₂H₅)₃ (SiP) and tetraethoxysilane Si(OC₂H₅)₄ (TEOS) in various ratios, under acidic conditions. The hydrolysis and initial polycondensation of SiP were studied by high-resolution ²⁹Si-NMR. Based on signal intensities, singnals due to the following oligomers were identified: R(OH)₂SiOSi(OH)(R)OSi(OH)₂, R(OH)₂SiOSi(OH)₂, R(OH)(OEt)SiOSi(OH)₂R, R(OH)(OEt)SiOSi(OH)₂R, R(OH)₂SiOSi(OH)(R)OSi(OH)₂R and [R(OH)SiO-]-₃. ²⁹Si NMR Quantitative analysis was performed on SiP–TEOS mixtures during the hydrolysis-condensation reactions and on the final gels. This provided information on the formation of the gels molecular structure. © 1996 John Wiley & Sons, Inc.     

Synthesis,Surface and Antimicrobial Activities of Novel Cationic Gemini Surfactants

A series of novel cationic gemini surfactants [C_nH_2n+1–O–CH₂–CH(OH)–CH₂–N⁺(CH₃)₂–(CH₂)₂]₂·2Br^? [ 3a (n = 12), 3b (n = 14) and 3c (n = 16)] having a 2‐hydroxy‐1,3‐oxypropylene group [?CH₂–CH(OH)–CH₂–O–] in the hydrophobic chain have been synthesized and characterized. Their water solubility, surface activity, foaming properties, and antibacterial activity have been examined. The critical micelle concentration (CMC) values of the novel cationic gemini surfactants are one to two orders of magnitude smaller than those of the corresponding monomeric surfactants. Furthermore, the novel cationic gemini surfactants have better water solubility and surface activity than the comparable [C_nH_2n+1–N⁺(CH₃)₂–(CH₂)₂]₂·2Br^? (n‐4‐n) geminis. The novel cationic gemini surfactants 3a and 3b also exhibit good foaming properties and show good antibacterial and antifungal activities.     

Low-Pressure Carbonylation of Benzyl Bromide with Palladium Complexes Modified with PNS (PNS = Ph2PCH2CH2C(O)NHC(CH3)2CH2SO3Li) or P(OPh)3. Structural Identification of Palladium-Catalyst Intermediate

The catalytic activities of two palladium complexes with water soluble phosphine PNS (PNS = Ph₂PCH₂CH₂C(O)NHC(CH₃)₂CH₂SO₃Li) (I) and phosphite P(OPh)₃ (II) were tested in the carbonylation of benzyl bromide in methanol at 40–50°C and 1 atm of CO. The first catalyst, (I), was formed in situ from PdCl₂(cod) and PNS, the second one, (II), was based on the PdCl₂(P(OPh)₃)₂ complex. At the ratio of [NEt₃]:[PhCH₂Br] equal to 2.5 the yields of phenylacetic acid methyl ester were 83–86% in the carbonylation with PNS and 100% in the carbonylation with P(OPh)₃. The palladium catalyst with P(OPh)₃ produced under the same conditions 70% of phenylacetic acid methyl ester in the carbonylation of benzyl chloride and 60% of 2-methylphenylacetic acid methyl ester in the carbonylation of 1-bromoethylbenzene. The lower rate of carbonylation of 1-bromoethylbenzyl bromide in comparison to that of benzyl bromide was explained by the lower rate of the substrate oxidative addition step leading to palladium benzyl complexes. Two palladium benzyl complexes, cis-PdBr(PhCH₂)(P(OPh)₃)₂ and trans-PdBr(PhCH(Me))(P(OPh)₃)₂ have been isolated and characterized (X-ray, ³¹P and ¹H NMR).     

Synthesis,properties, and application of novel silane-modified polyoxyethylene ether surfactants

Novel silane-modified polyoxyethylene ether surfactants (SMPES) were synthesized to improve the properties of water-based silicone rubber by reacting polyoxyethylene ether, RO(CH₂CH₂O)_nH (where R=nonylphenyl or dodecyl and n is 17 or 15), with 3-chloropropylalkoxylsilane, ClCH₂CH₂-CH₂SiR¹(OR²)₂ or CICH₂CH₂CH₂Si(OR²)₃ (where R¹=methyl and R²=methyl or ethyl). The structural characteristics of SMPES were indicated by Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance (NMR) spectroscopy, carbon NMR spectroscopy, silicon NMR spectroscopy, and electrospray ionization-mass spectrometry. The properties of SMPES were also investigated. SMPES were found to be good emulsifiers, with a low foaming power and low cloud point. The water-based silicone rubber prepared with SMPES exhibited a shorter tack-free time and resistance to frosting when it contacted water.     

Enantioselective Hydrogenation of Aromatic Ketones Catalyzed by a Mesoporous Silica‐Supported Iridium Catalyst

A mesoporous, silica‐supported, chiral iridium catalyst with a highly ordered dimensional‐hexagonal mesostructure was prepared by postgrafting the organometallic complex (1‐diphenylphosphino‐2‐triethylsilylethane)[(R,R)‐1,2‐diphenylethylenediamine]iridium chloride {IrCl[PPh₂(CH₂)₂Si(OEt)₃]₂[(R,R)‐DPEN] (DPEN=1,2‐diphenylethylenediamine)} on SBA‐15 silica. During the asymmetric hydrogenation of various aromatic ketones under 40 atm of hydrogen, the mesoporous, silica‐supported, chiral iridium catalyst exhibited high catalytic activity (more than 95% conversions) and excellent enantioselectivity (up to more than 99% ee). The catalyst could be recovered easily and used repetitively seven times without significantly affecting the catalytic activity and the enantioselectivity.     

Synthesis and Characterization of a Quaternized Glucosamide-Based Trisiloxane Surfactant

The synthesis of quaternized glucosamide‐based trisiloxane surfactant (QGS) of the general formula Me₃SiOSiMeR¹OSiMe₃ (R¹ = (CH₂)₃N⁺(CH₃)₂(CH₂)₂R², R² = glucosamide group) was described, and the surface activity properties of the surfactant were studied. The N‐[2‐(dimethylamino)ethyl]‐d ‐gluconamide was synthesized by amidation of the ethylenediamine with d ‐gluconolactone. The 3‐(3‐chloropropyl)‐1,1,1,3,5,5,5‐heptamethyltrisiloxane was prepared by the acid‐catalyzed reaction of a silane monomer. The QGS was prepared by quaternization of the precursor halogenated hydrocarbon with a tertiary amine. They were structurally characterized by IR, ¹H NMR and MS. And it reduced the surface tension of water to approximately 21 mN m^?1 at concentration levels of 10^?3 mol L^?1.     

Investigation of Conformational Behavior and Mobility in Linear Liquid Crystalline Polyesters by 13C Solid State NMR-Spectroscopy

Abstract

Splitting of resonance signal of CH₂ group of spacer was observed in ¹³C solid state NMR spectra of liquid crystalline (LC) polyester with siioxane spacer [-OC-Pb-OOC-CH = CH-COO-Ph-COO-CH₂?_? Si(CH₃)₂-O-Si(CH₃)2-CH₂-O-]_n in LC-state. We consider that there are two conformations of-COO-CH₂-Si(CH₃)2-group of spacer. These conformations are stabilized by steric interactions of CH₂ groups of siioxane fragments with ortho-protons of phenylene rings of mesogene. As a result, there are hindrances to both flips of the phenylene rings and conformational transitions in the spacers.     

Ethylene polymerization by 3‐oxa‐pentamethylene bridged asymmetric dinuclear titanocene/MAO system

An asymmetric 3‐oxa‐pentamethylene bridged dinuclear titanocenium complex (CpTiCl₂)₂(η⁵‐η⁵‐C₉H₆(CH₂CH₂OCH₂CH₂)C₅H₄) ( 1 ) has been prepared by treating two equivalents of CpTiCl₃ with the corresponding dilithium salts of the ligand C₉H₇(CH₂CH₂OCH₂ CH₂)C₅H₅. The complex 1 was characterized by ¹H‐, ¹³C‐NMR, and elemental analysis. Homogenous ethylene polymerization catalyzed using complex 1 has been conducted in the presence of methylaluminoxane (MAO). The influences ofreaction parameters, such as [MAO]/[Cat] molar ratio, catalyst concentration, ethylene pressure, temperature, and time have been studied in detail. The results show that the catalytic activity and the molecular weight (MW) of polyethylene produced by 1 /MAO decrease gradually with increasing the catalyst concentration or polymerization temperature. The most important feature of this catalytic system is the molecular weight distribution (MWD) of polyethylene reaching 12.4, which is higher than using common mononuclear metallocenes, as well as asymmetric dinuclear titanocene complexes like [(CpTiCl₂)₂(η⁵‐η⁵‐C₉H₆(CH₂)_nC₅H₄)] (n = 3, MWD = 7.31; n = 4, MWD = 6.91). The melting point of polyethylene is higher than 135°C, indicating highly linear and highly crystalline polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Two new siloxanic proton-conducting membranes: Part I. Synthesis and structural characterization

The development of stable polymer electrolytes having good proton conductivity, low cost and operating at medium temperatures represent a crucial step in the evolution of polymer electrolyte fuel cells. We describe two new siloxanic proton-conducting membranes that were synthesized through a two-stage protocol. In the first stage, a poly(methyl hydrosiloxane) precursor (P) bearing siloxane side chains with sulfonic acid groups was prepared. In the second step, the hydrolysis of pristine precursor or its derivative obtained by grafting siloxane chains on P yielded two types of membranes with the formulas {Si(CH₃)₃O[Si(CH₃)HO]_21.26[Si(CH₃)((CH₂)₃SO₃H)O]_1.8[Si(CH₃)((CH₂)₃Si(CH₃)₂O)O]₁₄Si(CH₃)₃}_n (A) and {Si(CH₃)₃O[Si(CH₃)HO]_21.26[Si(CH₃)((CH₂)₃SO₃H)O]_1.8[Si(CH₃)((CH₂)₃(Si(CH₃)₂O)_w)O]_v[Si(CH₃)((CH₂)₃Si(CH₃)₂O-)O]_14 − vSi(CH₃)₃}_n (B), with w = 20.31. Polymer membranes of A and B were prepared by means of a hot-pressing process at 80 °C and 10 t/cm². Scanning electron microscopy showed that A and B are rubbery materials with rough and transparent surfaces. Thermogravimetric investigations performed under air atmosphere disclosed that A and B are thermally stable up to at least 198 °C. DSC measurements yielded T_g(s) of −44 and −60 °C for A and B, respectively. The polymers exhibit ionic exchange capacities of 0.33 (A) and 0.15 meq/g (B). FT-IR and FT-Raman investigations revealed that the polymers consist of reticulated siloxane networks with pendant silicone chains having sulfonic acid groups.     

Rhodium catalysed hydroformylation using diphenylphosphine functionalised carbosilane dendrimers

Diphenylphosphine functionalised carbosilane dendrimers Si((CH₂)_nSi(CH₃)₂(CH₂PPh₂))₄ (n=2,3; generation 1–3) and Si((CH₂)_nSi(CH₃)(CH₂PPh₂)₂)₄ (n=2,3; generation 1–2) have been synthesised and used as ligands in the rhodium catalysed hydroformylation of 1-octene. The activity of the system depends on the size and flexibility of the dendrimeric ligand.     

Investigation of allyl‐capped carbosilane dendrimers used as crosslinker for silicone rubber

High‐temperature vulcanized silicone rubber was prepared by using allyl‐capped carbosilane dendrimers, in which the core molecules were Si(CH₂CH?CH₂)₄ and Ph₂Si(CH₂CH?CH₂)₂ as crosslinker and nanoscale reinforcing filler, respectively. Allyl‐capped carbosilane dendrimers improved the mechanical properties of silicone rubber. The optimum tensile strength and tear strength were 9.6 MPa and 31.0 kN/m, respectively, when using SiG_n(allyl)m as the crosslinker and 10.1 MPa and 32.0 kN/m, respectively, when using Ph₂SiG_n(allyl)m as the crosslinker. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1772–1775, 2006     

Synthesis of Ruthenium Hydride Complexes Containing beta‐Aminophosphine Ligands Derived from Amino Acids and their use in the H2‐Hydrogenation of Ketones and Imines

The new complexes RuHCl(PPh₂CH₂CHRNH₂)₂ and RuHCl(PPh₂CH₂CHRNH₂)(R‐ binap), R=H (Pgly), R=Me [(R)‐Pala] were prepared by the substitution of the PPh₃ ligands in RuHCl(PPh₃)₃ or RuHCl(PPh₃)[(R)‐binap] with beta‐aminophosphines derived from amino acids. The complex trans‐RuHCl(Pgly)[(R)‐binap] has been characterized by X‐ray crystallography. The complex trans‐RuHCl[(S)‐Ppro]₂ where (S)‐Ppro is derived from proline was also prepared and characterized by X‐ray crystallography. These were used as catalyst precursors in the presence of a base (KOPr‐i or KOBu‐t) for the hydrogenation of various ketones and imines to the respective alcohols and amines with H₂ gas (1–11 atm) at room temperature. Acetophenone was hydrogenated to (S)‐1‐phenylethanol in low ee (up to 40%) when catalyzed by the enantiomerically pure complexes. These complexes are especially active in the hydrogenation of sterically congested and electronically deactivated ketones and imines and are selective for the hydrogenation of CO bonds over CC bonds.     

Poly-n-alkyl-methylsiloxane als effektive BPA-Punkt- und Stockpunkterniedriger für Mineralöle

Poly-n-alkyl-methylsiloxanes: Effective Cloud Point and Pour Point Depressants for Petroleum Distillates Linear poly-n-alkyl-methylsiloxanes of the formulae (CH₃)₃Si-[OSi(CH₃)R]_n-OSi(CH₃)₃ with R = C₁₂H₂₅, C₁₄H₂₉, C₁₆H₃₃ and n ⩽ 8 were prepared by various synthetic methods. Both these substances and the analogous cyclic siloxane derivates [OSi(CH₃)R]_m (m = 3…6) were found to be effective cloud point and pour point depressants for petroleum middle distillates. Some ideas concerning the mechanism of could point depression are discussed.     

Synthesis and Characterization of 5-Coordinate Tungsten Hydride Anions: [(tBu3SiNH)(tBu3SiN=)2HWR]M

Treatment of (^tBu₃SiNH)(^tBu₃SiN=)₂WH ( 1 -H) with small alkyl anions (RM) afforded tungsten alkyl hydride anions [(^tBu₃SiNH)(^tBu₃SiN=)₂HWR)]M ( 3 -(R)M: R=CH₃, M=Li; R=ⁿBu, M=Li; R=^neoPe, M=Li; R=CH₂Ph (Bn), M=K (two isomers); R=CCH, M=Na; R=CH=CH₂ (Vy), M=Li). The saturated alkyl anions 3 -(R)M ( 3 -(R)M: R=CH₃, M=Li; R=ⁿBu, M=Li; R=^neoPe, M=Li; R=CH₂Ph (Bn), M=K) degraded via apparent 1,2-RH-elimination to produce the known [(^tBu₃SiN=)₃WH]M ( 2 -HM), but the acetylide ( 3 -(C₂H)Na) and vinyl ( 3 -(Vy)Li) anions converted to their hydrogenated isomers, [(^tBu₃SiN=)₃WVy]Na ( 2 -VyNa) and [(^tBu₃SiN=)₃WEt]Li ( 2 -EtLi), respectively. The structure of 3 -(ⁿBu)Li is reported, and a discussion of tungsten-hydride coupling constants in ^tBu₃SiX-ligated (X=O, NH, N) systems is given.     

Chitosan–organosilane hybrids—Syntheses,characterization, copper adsorption,and enzyme immobilization

New organic–inorganic hybrids SiGCX (X = 1 to 3) were prepared from the biopolymer chitosan with a degree of the deacetylation of 86% and three distinct silylating agents of the type (CH₃O)₃Si R NH₂ [R =  (CH₂)₃ ,  (CH₂)₃NH(CH₂)₂ and  (CH₂)₃NH(CH₂)₂NH(CH₂)₂ ]. Both chitosan and silylating agents have the amine groups crosslinking through linear glutaraldehyde units. Two stages were proposed for this synthetic method: crosslinking, and sol‐gel processes. The resulting dried hydrogels are amorphous, insoluble in organic as well as acidic or alkaline aqueous media, and exhibited a lamellae‐like surface morphology. The hybrids SiGCX (X = 2 and 3) have a larger adsorption capacity for copper ion than natural chitosan, with very similar kinetics of adsorption, defining a plateau after 1 h. The adsorption of copper increases with the organic chain length of the silylating agents: [(1.72 ± 0.05); (1.98 ± 0.06) and (2.49 ± 0.07)] × 10⁻² mmol/g for SiGCX (X = 1 to 3), respectively, and chitosan adsorbed (1.72 ± 0.05) × 10⁻² mmol/g. These hybrids presented a good capacity for immobilizing enzymes, which decreased with the increase of the organic chain length of the silylating agents, that is, from SiGC3 to SiGC1. The amount of catalase immobilized for the hybrids SIGCX (X = 1 to 3) is 29.03 ± 0.87; 25.79 ± 0.77, and 17.94 ± 0.54 mg g⁻¹, respectively, which is larger than the value of 12.21 ± 0.37 mg g⁻¹ obtained for chitosan. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 797–804, 2000