Zemin Xie

Controlled synthesis and characterization of poly[methyl(3,3,3-trifluoropropyl)siloxane] with selective end groups

Anionic ring-opening polymerization of 1,3,5-tris(trifluoropropylmethyl)cyclotrisiloxane in the bulk was studied using dilithium diphenylsilanediolate as an initiator (I); and N,N-dimethylformamide (DMF), bis(2-methoxyethyl)ether (Diglyme), and 1,2-dimethoxyethane (DME) as promoters (P). A detailed study on the kinetics of polymerization with different molar ratios of promoter to initiator ([P]/[I]) that were equal to 2.0, 4.0, and 6.0 revealed that the yield of linear polymers was the highest when [P]/[I] = 2.0 for all the promoters, among which DME was the most efficient promoter for suppressing the backbiting reactions. The reaction promoted by DME had a very broad “termination window” with the highest yield of linear polymer and very narrow molar mass distribution. The results of the matrix-assisted laser desorption/ionization time of flight mass spectrometry indicated that the intermolecular redistribution occurred during the process of polymerization. PMTFPS with end groups such as vinyl, hydroxyl, hydrogen and chloromethyl were prepared and characterized by 1H NMR, 29Si NMR and FT-IR. Polymers having vinyl end groups displayed higher thermo stability than those having hydroxyl end groups under nitrogen.

Synthesis and characterization of self-assembled three-dimensional flower-like iron(III) oxide–indium(III) oxide binary nanocomposites

Three-dimensional (3D) flower-like iron(III) oxide-indium( III) oxide (Fe2O3-In2O3) binary metal oxide nanocomposites were successfully fabricated by a simple and economical route based on an efficient ethylene glycol mediated process. Effects of the experimental parameters such as the ratio of Fe to In, type of acid absorber, solvent, and reaction temperature and time on the morphology of the nanocomposite were discussed in detail. The nanocomposites Fe2O3-In2O3 with flower-like morphology were readily obtained by annealing the precursor. The possible reaction mechanism leading to the precursor and the self-assembly process was also proposed. The results of the thermogravimetric analyses indicated that 3D flower-like Fe2O3-In2O3 binary metal oxide nanocomposites can be used as fillers to significantly enhance the thermal resistance of silicone rubber under nitrogen.

Carborane-Containing Solvent-Free Liquid Silicone Resin: Synthesis, Characterization, and High-Temperature Adhesive Properties

GRAPHICAL ABSTRACT Abstract A series of carborane-containing solvent-free liquid silicone resins were synthesized by a hydrosilylation reaction with silicone resins containing different vinyl contents and 1,7-bis (3-hydridotertramethyldisiloxanyl)-m-carborane (HCB). The structure and thermal properties of the silicone resins were characterized by nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), as well as dynamic mechanical analysis (DMA), respectively. The cured silicone resins containing carborane showed better thermal stability and thermal oxidative stability than its carborane-free counterpart. DMA showed that cured silicone resins had high tan δ value thus providing good prospects for damping material applications. Furthermore, adhesive properties of silicone resin adhered to stainless steel at various conditions were evaluated by lap shear strength (LSS) test. It was found that the LSS of adhesive containing carborane was higher than that of carborane-free adhesive at per testing temperature. The results also showed that the bonding strength of adhesive increased with increasing carborane content.

Nonequilibrium Anionic Ring-opening Polymerization of Tetraphenyltetramethylcyclotetrasiloxane (D4Me,Ph) Initiated by Sodium Isopropoxide

GRAPHICAL ABSTRACT Abstract The nonequilibrium anionic ring-opening polymerization (NAROP) of tetraphenyltetramethylcyclotetrasiloxane (D4Me,Ph) in the presence of initiator (sodium isopropoxide) and promoters including 12-crown-4, N-methyl-2-pyrrolidinone (NMP), N,N-dimethylformamide (DMF), and diglyme was investigated. It was found that the polymerization could be accelerated sharply by the increase of reaction temperature, as well as the mole ratio of promoter to initiator ([p]/[i] ratio). The NAROP rate of D4Me,Ph decreased in the order of promoters: 12-crown-4>> NMP >DMF >diglyme. In the presence of NMP and sodium isopropoxide ([p]/[i] ratio = 3.0, 10 h at 70°C), the polydispersity index (PDI) of the poly(methylphenylsiloxane) obtained is 1.52, and the conversion rate of the monomer can reach over 90%. The byproduct pentaphenylpentamethylcyclopentasiloxane (D5Me,Ph), which encountered in the 12-crown-4 promoted system upon prolonged reaction time, was not observed according to the 29Si NMR of the reaction mixtures. In conclusion, NMP turned out to be the best choice among those promoters to realize the NAROP of D4Me,Ph.

High-yielding and facile synthesis of organosilicon compounds containing a m-carboranylmethyl group

An efficient method for the synthesis of organosilicon compounds containing m-carboranylmethyl was developed, which afforded the products in good to excellent yields (up to 88%) compared to the literature methods affording a 38% yield. Moreover, the generated intermediate 5 containing a Si-Br bond could be functionalized conveniently.

Mechanism of the antioxidation effect of α-Fe2O3 on silicone rubbers at high temperature

The high temperature resistance of silicone rubber (SR) could be significantly improved by adding hematite (α-Fe2O3). In this study, the variation of α-Fe2O3 and polysiloxanes was investigated by ultraviolet-visible absorption spectroscopy, X-ray diffraction, Mossbauer spectroscopy, and 29Si NMR spectroscopy after SR aging for 12 h in air at 350 °C. The results indicate that Fe3+ is reduced to Fe2+ by organic free radicals (R˙) in the process of aging. Fe3+ captures R˙ to protect the polysiloxanes from being destroyed and is transformed into Fe3O4. Moreover, magnetic Fe3O4 is only found in the inner layer of SR; however, it is not detected in the outer layer. Therefore, a new mechanism of antioxidation is proposed: on the outer part of SR, the reduction–oxidation cycle of Fe3+ is formed because of sufficient oxygen; however, inside the SR, α-Fe2O3 is gradually reduced to Fe3O4.

2,2,4,4-Tetra­phenyl-1,3-bis­(3,3,5,5-tetra­methyl-1,1-diphenyl-5-vinyl­trisilox­an-1-yl)­cyclo­disilazane

The title molecule, C60H70N2O4Si8, lies on an inversion center. In the asymmetric unit, one of the phenyl rings is disordered over two sets of sites with refined occupancies 0.58 (2) and 0.42 (2). In addition, in two substitution sites of the terminal dimethyl(vinyl)silyl unit, a methyl group and the vinyl group are disordered over the same site with refined occupancies 0.523 (13) and 0.477 (13).

1,1,3,3,5,5,7,7-Octa­phenyl-2,6-dioxa-4,8-diaza-1,3,5,7-tetra­silacyclo­octa­ne

The title molecule, C48H42N2O2Si4, lies on a twofold rotation axis. The eight-membered ring has a slightly distorted boat conformation.

FACILE SYNTHESIS OF 1,3-DICHLOROTETRAORGANODISILAZANES

A new 1,3-dichlorodisilazane, 1,3-dichloro-1,3-dimethyl-1,3-divinyldisilazane (DMDV), was prepared from the trans-silylation reaction of hexamethyldisilazane (MMN) and methylvinyldichlorosilane. The reactions between MMN and other dichlorosilanes, R2SiCl2 (R = Me, Ph) in the absence of catalyst were also investigated, and the expected, 1,3-dichlorosilazanes, (ClSiMe2)2NH and (ClSiPh2)2NH were obtained, respectively.