Novel anion-exchange organic–inorganic hybrid membranes: Preparation and characterizations for potential use in fuel cells

A new series of supported anion-exchange organic–inorganic hybrid membranes were prepared by quaternizing the copolymer of vinylbenzyl chloride (VBC) and γ-methacryloxypropyl trimethoxy silane (γ-MPS) and then applying a sol–gel reaction to the copolymer and monophenyltriethoxysilane (EPh). The membranes were characterized for potential use in fuel cells. The results show that the physicochemical properties, including ion-exchange property, hydrophilicity, and thermal/chemical stability, can be easily controlled by adjusting the quaternization extent of the copolymer and the dosage of EPh. The hybrid membranes have relatively strong alkali resistance, high temperature tolerance (thermal degradation temperature in air, Td, in the range of 250–300 °C), high tensile strength (TS) and elongation at break (E_b). The hydroxyl ion conductivity is in the range of 2.27–4.33 × 10⁻⁴ S/cm.     

A new silane precursor with reduced polymerization shrinkage

There is a growing interest in precursor molecules for the sol-gel process which allow the formation of inorganic-organic copolymers, the so-called ORMOCER^®s, with no or only low shrinkage. A new silane type, the spiro ortho ester silanes, which can be polymerized by a ring opening reaction has been developed in order to overcome problems associated with loss of precise dimension and poor cohesion or stresses in coatings or in bulk materials caused by shrinkage during the curing step. In this paper, the synthesis of the new reactive silane precursor, the incorporation into the sol-gel process and the ring-opening reaction that can be UV-induced, for instance, will be described. First investigations show that the last reaction step is accompanied by a volume change of only <0.30 vol. -%.     

Chemically stable hybrid polymer electrolyte membranes prepared by radiation grafting,sulfonation, and silane‐crosslinking techniques

To prepare a crosslinked hybrid polymer electrolyte membrane (PEM) with high chemical stability, a silane monomer, namely p‐styryltrimethoxysilane (StSi), was first grafted to poly(ethylene‐co‐tetrafluoroethylene) (ETFE) film by γ‐ray preirradiation. Hydrolysis‐condensation and sulfonation were then performed on the StSi‐grafted ETFE (StSi‐g‐ETFE) films to give them crosslinks and proton conductibility, respectively. Thus, a crosslinked proton‐conducting hybrid PEM was obtained. The crosslinks introduced by the silane‐condensation have an inorganic ? Si? O? Si? structure, which enhance the chemical and thermal stabilities of the PEM. The effect of the timing of the hydrolysis‐condensation (before or after sulfonation) and the sulfonation method (by chlorosulfonic acid or H₂SO₄) on the properties of the resulting hybrid PEMs such as ion‐exchange capacity, proton conductivity, water uptake, chemical stability, and methanol permeability were investigated to confirm their applicability in fuel cells. We conclude that the properties of the new crosslinked hybrid StSi‐grafted PEMs are superior to divinylbenzene (DVB)‐crosslinked styrene‐grafted membranes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5559–5567, 2008     

Preparation and properties of alkoxy(methyl)silsesquioxanes as coating agents

Polysilsesquioxanes were prepared through the acid‐catalyzed hydrolytic polycondensation of triethoxy(methyl)silane, triisopropoxy(methyl)silane, or triisobutoxy(methyl)silane and subjected to dip coating to form coating films. The film formation depended on the polarity and crystallinity of the substrate, and a correlation was found between the substrate and polysilsesquioxane solubility parameters. When the coating film was heated, thermal condensation occurred at about 500 °C between hydroxy groups or between hydroxy and alkoxy groups. The methyl group attached to silicon decomposed, and siloxane bonding formed at about 800 °C. The adhesion and hardness of the coating films were evaluated with the Japanese Industrial Standard K5400 protocol, and they increased with increases in the heating time and heat‐treatment temperature. The refractive index of the coating films decreased when the heat‐treatment temperature was increased to 500 °C because of the combustion of organic groups. In contrast, the surface electric resistance increased with the heat‐treatment temperature up to 500 °C. The dielectric constant was 2.6–2.8 and decreased with an increases in the molecular weight and the degree of crosslinking of the polysilsesquioxanes. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3676–3684, 2004     

Effects of refractive index modifiers and UV light on an epoxy-functional inorganic-organic hybrid sol-gel derived thin film system

Thin film systems consisting of (3-glycidyloxypropyl)trimethoxysilane (GDPTMS), dimethyldimethoxysilane (DMDMOS) and, either zirconium(IV) n-propoxide (Zr(OPrⁿ)₄) or diphenyldimethoxysilane (DPDMS) were synthesised via the sol-gel method. GDPTMS and DMDMOS were employed as the main network formers, whereas Zr(OPrⁿ)₄ or DPDMS was both a network former and a refractive index modifier. The comparative effects of Zr and DPDMS content, and UV light on the optical and thermal properties of the system were evaluated. Refractive index measurements and cross-sectional scanning electron microscopy of the resultant thin films were performed. The thermal stability of each system, in terms of temperature at 10% mass loss, was characterised by dynamic thermogravimetry. It was demonstrated that the selection of refractive index modifier along with UV irradiation plays an important role in tuning the optical and thermal properties of an epoxy-functional inorganic-organic hybrid sol-gel derived thin film system.     

The stretching fundamental bands ν1, ν2 and ν4 of HSiD3

The ν₁(A₁), Si-H stretching, ν₂(A₁) and ν₄(E), Si-D stretchings, fundamental bands of HSiD₃ have been recorded at an effective resolution of ca. 0.003 cm⁻¹ between 2080 and 2280 cm⁻¹ and between 1480 and 1720 cm⁻¹, respectively. Ro-vibrational transitions of the H²⁸SiD₃ isotopologue have been assigned in the two spectral ranges, about 700 belonging to ν₁, with J′ up to 25 and K up to 21, and about 1600 to the ν₂/ν₄ dyad, with J′ up to 24 and K′ up to 19. The spectra of all the bands evidence the existence of several perturbations. The transitions of ν₁ have been analyzed either neglecting or including in the model A₁/E Coriolis-type interactions with nearby dark states. The υ₂ = 1 and υ₄ = 1 states have been fitted simultaneously taking into account several ro-vibrational interactions between them and, in addition, with the υ₅ = 2, l = 0 component, and with few other close dark states. The standard deviation of the fit for both ν₁ and the ν₂/ν₄ dyad is, however, more than one order of magnitude larger than the estimated experimental precision and is independent on the adopted model.     

Gas-phase ion chemistry in XH4--C3H4--ZH3 (X==Si, Ge; Z==N, P) mixtures

The gas-phase ion chemistry of silane-allene-ammonia, germane-allene (or propyne)-ammonia (or phosphine) systems was studied by ion trap mass spectrometry. Reaction sequences were determined and rate constants were measured for the main processes observed. The mixture containing silane displays higher reactivity with respect to that with germane. Comparison with analogous systems provides useful information about the reactivity of different hydrocarbon molecules and the different affinities of silicon and germanium towards nitrogen and phosphorus. The most interesting product ions observed are those containing Si (or Ge), C and N (or P) elements together, as these ion species may be considered precursors of doped amorphous carbides, which are widely used in semiconductor devices.     

Fracture behaviors of silane‐cured metallocene‐catalyzed polyethylene thermoplastic vulcanizate

Silane moisture‐cured metallocene‐catalyzed polyethylene (mPE) blend to form a novel thermoplastic vulcanizate (TPV) has been prepared. Metallocene polyethylenes with two different levels of comonomer contents were grafted with various amounts of vinyltriethoxy silane. As a result, tensile strength varies slightly with increasing the levels of silane concentrations, at all test temperatures. Tear strength generally decreases with reduced energy dissipation, at higher degrees of cure. “Threshold” fracture energy is roughly proportional to the reciprocal square root of Young's modulus. By relating tensile strength to tear strength, it was found that the corrected average depth of flaw is in the range of 29.3 ± 7.2 μm, which successfully confirms the extension of Rivlin and Thomas's theory for conventional elastomers to TPVs under an elaborate treatment, due to the limitation of the theory. Cutting strength of mPE TPVs gives an intermediate value when compared with that of crystalline plastics and conventional elastomers, which further signifies the importance of crystalline yielding even in the nanofracture zone of deformation. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2207–2218, 2005     

Dynamics of liquid silane

Neutron scattering of cold neutrons from liquid silane at 137° K and 98°K is explained on the basis of a simple model. The rotational diffusion constant,D _r, and the delay time,τ ₀, after which rotational diffusion may be said to occur are derived on the basis of this model. At 137° K we getD _r=0.22×10¹³ sec⁻¹ andτ ₀=0.68×10⁻¹³ sec. At 98°KD _r (=0.06×10¹³ sec⁻¹) is down by a factor of more than three butτ ₀=(0.54×10⁻¹³ sec) shows only a small change. By comparison with data on liquid CH₄ it is concluded that the law of corresponding states is not applicable for describing rotational dynamics of CH₄ and SiH₄. Rotational motions in SiH₄ are more hindered than in CH₄ at the same reduced temperature.