Siloxane elastomers, properties

At AWE, the Lewis acid-catalyzed bulk polymerization route has been the main synthesis route to poly(m-carborane-siloxane) elastomers. Our selection has been based on considerations of safety, availability of key reagents, and ease of scale-up operations. An understanding of the physical and chemical properties of these materials, and how these properties can be modified through the synthesis process, is essential in order to develop materials of controlled characteristics. 

Atomic oxygen is a highly reactive species that can pose serious problems for spacecraft in low Earth orbit due to degradation of materials of construction. In the case of siloxane elastomers and coatings88,89, it has been shown that surface oxidation occurs to give a silica layer which then protects the bulk material from further oxidation, with the result that little loss of physical properties occurs. 

In the case of siloxane elastomers, the testing of mechanical properties is of particular importance. Elongation or tensile measurements are used almost to the exclusion of other types of mechanical tests, probably because of their simplicity. In this way, structural information is obtained about the networks, such as their degrees of cross-linking.92 Measurements of the ultimate strength (modulus at rupture), and the maximum... 

Han, Y Zhang, J. Yang, Q. Shi, L. Qi, S. Jin, R., Novel Polymethoxysiloxane-Based Crosslinking Reagent and Its In-Situ Improvement for Thermal anad Mechanical Properties of Siloxane Elastomer. J. Appl. Polym. Sci. 2008,107, 3788-3795. 

Mayer, B. P. Lewicki, J. P. Weisgraber, T. H. Small, W. Chinn, S. C. Maxwell, R. S., Linking Network Microstructure to Macroscopic Properties of Siloxane Elastomers Using Combined Nuclear Magnetic Resonance and Mesoscale Computational Modeling. Macromolecules 2011,44,8106-8115. 

Urayama, K. Kawamura, T. Kohjiya, S., Structure-Mechanical Property Correlations of Model Siloxane Elastomers with Controlled Network Topology. Polymer 2008, 50, 347-356. 

TABLE 9.1 Properties of Typical Commercial Siloxane Elastomers [9]... 

McCai thy D W, Mark J E and Schaffer D W (1998) Synthesis, structure, and properties of hybrid organic-inorganic composites based on polysiloxaiies I Poly(dimethyl-siloxane) elastomers containing silica, J Polym Sci Part B Polym 36 1167-1189. 

---