Siloxanes properties

J.P. Cohen-Addad, NMR approach to siloxane properties Melts, gels, silica mixtures. In S.J. Clarson and J.A. Semiyen (Eds.), Siloxane Polymers, Prentice Hall, Englewood Cliffs, 1993, p. 511. 

Davis GC, Heath BA, Gildenblatt G (1984) Polyimide-siloxane properties and characterization for thin film. Electronic Applications in Ref 1 847-869... 

Because of their monofiinctionality, the title compounds may be used as a silicone offset for many organic molecules and additives. While the monosilanol oil is prone to spontaneous condensation reactions and has limited pot life, the amino- and chlorofiinctional fluids will confer the silicone haptics, surface tension, weatherability, and other sought-after siloxane properties onto the organic formulation. 

Cohen-Addad, J. P., NMR Approach to Siloxane Properties Melts, Gels, Silica Mixtures. In Siloxane Polymers, Clarson, S. J. Semiyen, J. A., Eds. Prentice Hall Englewood Cliffs, NJ, 1993 pp 511-566. 

Synonyms Ethylmethyl, methyl (2-phenylpropyl) siloxane Properties Cl. to It. amber vise, liq. insol. in water sp. gr. 1.01 vise. 1000-2000 cSt m.p. < 0 C b.p. > 205 C flash pt. (COC) 209 C Hazardous Decomp. Prods. Org. acid vapors, formaldehyde and silicon dioxide HMIS Health 1, Flammability 1, Reactivity 0... 

Table 2. Properties of Hydride Functional Organosilanes, Siloxanes, and Silazanes ...

Many of the unique properties of siUcone oils are associated with the surface effects of dimethylsiloxanes, eg, imparting water repeUency to fabrics, antifoaming agents, release liners for adhesive labels, and a variety of poHshes and waxes (343). Dimethylsilicone oils can spread onto many soHd and Hquid surfaces to form films of molecular dimensions (344,345). This phenomenon is greatly affected by even small changes in the chemical stmcture of siloxane in the siloxane polymer. Increasing the size of the alkyl substituent from methyl to ethyl dramatically reduces the film-forming abiUty of the polymer (346). The phenyl-substituted siUcones are spread onto water or soHd surfaces more slowly than PDMS (347). 

Performance of coupling agents in reinforced composites may depend as much on physical properties resulting from the method of appHcation as on the chemistry of the organofunctional silane. Physical solubiUty or compatibiUty of a siloxanol layer is determined by the nature and degree of siloxane condensation on a mineral surface. 

The siloxane Si—O link has a number of interesting properties which are relevant to the properties of the polyorganosiloxanes. TTiese will be dealt with later. 

As another consequence of the properties of the siloxane bond, the value of n in the common linear trimethylsiloxy-endblocked-PDMS, (M-D -M) can vary from zero to tens of thousands giving a range of viscosity from 0.65 to 2,500,000 centipoise to the polymeric material. This relationship between viscosity and polymer chain length allows PDMS polymers to vary in form from water-like fluids to a flowable gum, while retaining the same chemical character. 

Once cured, PDMS networks are essentially made of dimethylsiloxane polymeric chains crosslinked with organic linkages. The general and inherent molecular properties of the PDMS polymers are therefore conferred to the silicone network. Low surface energy and flexibility of siloxane segments are two inherent properties very useful in adhesion technology. 

PDMS based siloxane polymers wet and spread easily on most surfaces as their surface tensions are less than the critical surface tensions of most substrates. This thermodynamically driven property ensures that surface irregularities and pores are filled with adhesive, giving an interfacial phase that is continuous and without voids. The gas permeability of the silicone will allow any gases trapped at the interface to be displaced. Thus, maximum van der Waals and London dispersion intermolecular interactions are obtained at the silicone-substrate interface. It must be noted that suitable liquids reaching the adhesive-substrate interface would immediately interfere with these intermolecular interactions and displace the adhesive from the surface. For example, a study that involved curing a one-part alkoxy terminated silicone adhesive against a wafer of alumina, has shown that water will theoretically displace the cured silicone from the surface of the wafer if physisorption was the sole interaction between the surfaces [38]. Moreover, all these low energy bonds would be thermally sensitive and reversible. 

Stepto, R.F.T., Theoretical aspects of conformation-dependent properties. In Clarson, S.J. and Semiyen, J.A. (Eds.),. Siloxane Polymers, Polymer Science and Technology Series. PTR Prentice Hall, Englewood Cliffs, NJ, 1993, pp. 373-414. 

St. Clair et. al. investigated a series of maleimide and nadimide terminated polyimides and developed LARC-13 [8,9]. Changing the terminal group from maleimide to nadimide, the value of the lap shear strength of a titanium lap shear joint increased from 7 to 19 MPa [9]. They also added an elastomeric component to the adhesive formulation. The introduction of 15 wt% of a rubbery component, ATBN (amine terminated butadiene nitrile polymer) and ADMS (aniline terminated polydimethyl siloxane) enhanced the adhesive properties as follows 19 MPa to 25 MPa (ATBN) titanium T-peel strength 0.2 kN/m to 1.4... 

An artificial neural network based approach for modeling physical properties of nine different siloxanes as a function of temperature and molecular configuration will be presented. Specifically, the specific volumes and the viscosities of nine siloxanes were investigated. The predictions of the proposed model agreed well with the experimental data [41]. 

R. Keshavaraj, R. W. Tock, R. S. Narayan, and R. A. Bartsch, Fluid Property Prediction of Siloxanes with the Aid of Artificial Neural Nets, Polymer-Plastics Technology and Engineering, i5(6) 971-982 ( 996). 

Silane coupling agents may contribute hydrophilic properties to the interface, especially when amino functional silanes, such as epoxies and urethane silanes, are used as primers for reactive polymers. The primer may supply much more amine functionality than can possibly react with the resin at the interphase. Those amines that could not react are hydrophilic and, therefore, responsible for the poor water resistance of bonds. An effective way to use hydrophilic silanes is to blend them with hydrophobic silanes such as phenyltrimethoxysilane. Mixed siloxane primers also have an improved thermal stability, which is typical for aromatic silicones [42]. 

Another approach to molecular assembly involves siloxane chemistry [61]. In this method, the electrically or optically active oligomers are terminated with tii-chlorosilane. Layers are built up by successive cycles of dip, rinse, and cure to form hole transport, emissive, and electron transport layers of the desired thicknesses. Similar methods have also been used to deposit just a molecular monolayer on the electrode surface, in order to modify its injection properties. 

An important property of these siloxane phases is their stability under the conditions used in most chromatographic separations the siloxane bonds are attacked only in very acidic (pH < 2) or basic (pH > 9) conditions. A large number of commercial bonded-phase packings are available in particle sizes suitable for HPLC.48... 

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