Facile route to synthesis of functionalised poly(methylalkoxy)siloxane under mild and aerobic conditions in the presence of platinum catalysts

A facile and high yield method of synthesis of novel and functional poly(methylalkoxy) siloxanes is reported. The Si–H groups of poly(methylhydrogen) siloxanes (PMHS) were treated with various simple (primary, secondary, tertiary) alcohols (1a–10a) in the presence of platinum based catalysts (Speier’s and Karstedt’s catalysts). Also oxyethylene, aldehyde, epoxide, halogen and allyl grafted polysiloxane were smoothly and quantitatively prepared by the alcoholysis between linear siloxanes polymer and functional alcohols (11a–20a) with use of Karstedt’s catalysts. It is found that alcoholysis reaction in the presence of the Karstedt’s catalyst proceed faster than Speier’s catalyst .In addition, the rate of alcoholysis reaction is dependent on amount of the catalyst and reaction temperature. The polymers prepared were characterized by IR, NMR spectroscopy and GPC analysis.     

1,4-bis[2,2-bis(trimethylsilyl)ethenyl]benzene: Regioselective ring opening of its α,β-epoxybis(silane) with some nucleophiles

The Peterson olefination reaction of terephthalaldehyde with tris(trimethylsilyl)methyllithium, (Me₃Si)₃CLi, in Et₂O gives disubstituted vinylbis(silane) 1 which reacts with MCPBA in CH₂Cl₂ at r.t. to afford mixture of mono and disubstituted epoxybis(silanes) 3 and 2. Vinylbis(silane) 1 can be completely converted into epoxybis(silane) 2 with an excess amount of MCPBA. The compound 2 was reacted with various reagents such as HX (X = Cl, Br), H₂SO₄, LiAlH₄ and MeLi/CuI and give the related products.     

Micromechanical characterizing elastic,thermoelastic and viscoelastic properties of functionally graded carbon nanotube reinforced polymer nanocomposites

In this work, elastic, thermoelastic and viscoelastic properties of functionally graded carbon nanotube reinforced polymer nanocomposites are investigated using a 3-dimensional micromechanics-based approach. The main advantage of the proposed micromechanical model is its ability to give closed-form formulation for predicting the effective properties of nanocomposites. In the micromechanical modeling, the interphase formed due to non-boned van der Waals interaction between the continuous CNT and polymer matrix is considered through employing an individual representative volume element. The validity of the model is examined by comparing its results with other theoretical approaches and experimental data available in the literature. The effects of various types of CNTs arrangement in the matrix, i.e. uniform distribution and different functionally graded distributions on the elastic, thermoelastic and viscoelastic properties of polymer nanocomposites are investigated in detail. Furthermore, random arrangement of CNTs in the matrix is modelled. The influences of CNT/polymer matrix interphase and CNT volume fraction on the effective properties of nanocomposites are also studied. Finally, the viscoelastic response of nanocomposites under multiaxial loading is extracted and interpreted.     

Synthesis and reactions of [tris(trimethylsilyl)methyl]ethyl dichlorosilane

The crowded dichlorosilane TsiSiEtCl₂, (1), (Tsi = (Me₃Si)₃C) was prepared from the reaction between EtSiCl₃ and TsiLi, then it was reduced with LiAlH₄ to give TsiSiEtH₂, (2). The hydride (2) was then treated with two equivalents of ICl/CCl₄ or Br₂/CCl₄ to produce TsiSiEtI₂, (3), and TsiSiEtBr₂, (4), respectively. The reaction of compound (2) with one equivalent of ICl/CCl₄ gives TsiSiEtHI, (5). This product reacted with H₂O/dioxane in the presence of AgClO₄ or with dry MeOH to produce TsiSiEtHOH, (6), and TsiSiEtHOMe, (7), respectively. The compound (3) reacted with H₂O in DMSO/CH₃CN to give TsiSiEt(OH)₂, (8), and the compound TsiSiEtIOMe, (9), was prepared from the reaction of the compound (7) with ICl/CCl₄. When the dichloride (1) was treated with NaOMe/MeOH it gave (Me₃Si)₂CHSiEt(OMe)₂. It is suggested that the reaction proceeds through an elimination-addition mechanism. The dichloride (1) was also treated with KSCN, NaN₃ or NaOCN in CH₃CN to give S_N2 substitution products. All the new products were characterized by FTIR, ¹H NMR, and ¹³C NMR spectroscopy, mass spectrometry and elemental analysis.     

A powerful, practical and chemoselective synthesis of 2-anilinoalkanols catalyzed by Bi(TFA)3 or Bi(OTf)3 in the presence of molten TBAB

A facile and efficient synthesis of β-amino alcohols by ring opening of epoxides with anilines in good to excellent yields in the presence of catalytic amounts of Bi(TFA)₃ or Bi(OTf)₃ via the use of molten tetrabutylammonium bromide (TBAB) as an ionic liquid is described. In addition, the observed chemoselectivity can be considered as a noteworthy advantage of this method.     

One-pot, novel chemical modification of glycidyl methacrylate copolymers with very bulky organosilicon side chain substituents

Glycidyl methacrylate (GM) random copolymers with styrene and methylstyrene (in a 1:1 and 1:3 mole ratio) were synthesized by solution free radical polymerizations at 70 ± 1 °C using α,α′-azoisobutyronitrile as an initiator. The copolymer compositions were obtained using related ¹H NMR spectra and the polydispersity indices of the copolymers determined using gel permeation chromatography (GPC). Both types of polymer could be modified by incorporation of the highly sterically demanding tris(trimethylsilyl)methyl substituent (Me₃Si)₃C-(Tsi = trisyl) through the ring opening reaction of the epoxy groups in copolymers. Chemical modification was determined by ¹H NMR and infrared spectroscopies. The glass transition temperature T_g of all copolymers was determined by differential scanning calorimetry (DSC). The T_g value of the copolymers containing bulky trisyl groups was found to increase with incorporation of trisyl groups in polymer structures. The presence of trisyl groups in the polymer side chain created new macromolecules with novel modified properties and potential use as membranes for fluid separation.     

Enhancement of Photocatalytic Efficiency of TiO2 by Supporting on Clinoptilolite in the Decolorization of Azo Dye Direct Yellow 12 Aqueous Solutions

Structure and physico‐chemical properties of a photocatalyst, especially surface area and absorption ability, were correlated to catalytic activities in photodegradation of dye pollutants in water. In this investigation photocatalytic degradation of azo dye Direct yellow 12 (Chrysophenine G) in water was studied. Titanium(IV) oxide was supported on Clinoptilolite (CP) (Iranian Natural Zeolite) using solid‐state dispersion (SSD) method. The results show that the TiO₂/Clinoptilolite (SSD) is an active photocatalyst. The maximum effect of photo degradation was observed at 10 wt.% TiO₂, 90 wt.% Clinoptilolite. A first order reaction with k = 0.0108 min^?1 was observed. The effects of some parameters such as pH, amount of photocatalyst, initial concentration of dye were examined.     

Glass transition temperature modification of acrylic and dienic type copolymers of 4-chloromethyl styrene with incorporation of (Me3Si)3C- groups

The new functional styrenic monomer, 4-trisylmethyl styrene (TsiMS) [Tsi=trisyl=tris(trimethylsilyl)methyl], was synthesized by reacting 4-chloromethyl styrene (CMS) with trisyllithium (TsiLi) in tetrahydrofuran (THF) solvent in the presence of copper chloride (CuCl). Attempt for the free radical polymerization of TsiMS by α,α^′-azobis(isobutyronitrile) (AIBN) as an initiator at 70 ± 1 °C failed for several periods of times. This result showed that the trisyl group is a highly sterically hindered substituent and, subsequently, TsiMS becomes resistant for polymerization. Therefore, for preparation of new methacrylic, acrylic and dienic copolymers of TsiMS, we firstly synthesized the copolymers of CMS with different monomers such as methyl methacrylate (MMA), ethyl methacrylate (EMA), methyl acrylate (MA), ethyl acrylate (EA), n-butyl acrylate (BA) and isoprene (IP) by free radical polymerization method in toluene solution at 70 ± 1 °C using AIBN initiator to give the copolymers I-VI in good yields. The copolymer compositions were obtained using related ¹H NMR spectra and the polydispersity indices of the copolymers determined using gel permeation chromatography (GPC). The trisyl groups were then covalently attached to the obtained copolymers as side chains by reaction between excess of TsiLi and benzyl chloride bonds of CMS units, to give the copolymers - in 80-92% yields. All the resulted polymers were characterized by FT-IR, ¹H NMR and ¹³C NMR spectroscopic techniques. The solubility of all the copolymers was examined in various polar and non-polar solvents. The glass transition temperature (T_g) of all copolymers was determined by differential scanning calorimetry (DSC) apparatus. The T_g value of copolymers containing bulky trisyl groups was found to increase with incorporation of trisyl groups in polymer structures. The presence of trisyl groups in polymer side chains, create new macromolecules with novel modified properties.     

Preparation of tris(trimethylsilyl)methyl (“trisyl”) derivatives of silicon

Treatment of (Me₃Si)₃CLi (“trisyl”lithium, TsiLi) with appropriate silicon halides has given a range of compounds of the type (Me₃Si)₃CSiRR′X; e.g., TsiSiCl₃, TsiSiMeCl₂, TsiSiMe₂X (X = Cl, OMe), TsiSiPh₂X (X = F, Cl, OMe), and TsiSiPhMeH. The trisyl group causes very large steric hindrance to nucleophilic displacements at the silicon to which it is attached, so that (unless one or more hydride ligands are present) most of the common displacements at silicon do not occur. However, halides can be reduced to hydrides by LiAlH₄, and the hydrides can be converted into halides in electrophilic displacements by hallogens. The presence of even one hydride ligand markedly reduces the hindrance, so that, for example, TsiSiPhHI reacts with refluxing methanol to give TsiSiPhH(OMe).