The Karstedt-catalyzed hydrosilylation reaction used in curing of silicone release coatings was investigated using first-principle quantum mechanical techniques (density functional theory) as well as semiempirical methods to estimate solubility parameters. The results we obtain for the catalytic cycle indicate, in agreement with experimental results, that hydrosilylation occurs easily at room temperature. The detailed mechanism we suggest contains the key features of the models previously proposed in the literature by Lewis and ChalkHarrod and adds quantitative estimates of reaction energies and barriers. On the basis of the energy profile for the catalytic cycle in the presence of inhibitor molecules and on solubility parameters for the species involved in the reaction, we conclude that the role of the inhibitors we considered is to phase-separate the catalyst from the substrate. The reaction is thus quenched by introducing a microscopic second phase that interferes with the homogeneous reaction.
A high-throughput method for screening the moisture vapor transmission rate of barrier films was developed. This moisture high-throughput screening (MHTS) technique is based upon a Nafion-crystal violet (CVN) sensor that changes color from yellow to green upon absorption of water. Using an appropriate set of known standards, the slope of absorbance (at 630 nm) as a function of time can be converted into moisture vapor transmission rate (MVTR) values that agree with those obtained using ASTM F1290. High-throughput screening was demonstrated by depositing 20 emulsion-based poly(vinylidene chloride) films, using a 48-well template, of varying thicknesses onto the CVN sensor film and aging at 40 degrees C and 90% relative humidity for 72 h. MVTR values were accurately determined to a level of 0.9 g/m(2).day, at which point side-diffusion of moisture between the barrier and sensor films prevented observation of lower values. Larger sample size and edge-sealing are two proposed methods for improving the sensitivity of MHTS.
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