Vinyl-substituted silphenylene siloxane copolymers: Novel high-temperatureelastomers

The synthesis of a series of vinyl-substituted silphenylene siloxane polyme rs of high molecular weight is described. Si-29 NMR spectroscopy indicates that the polymers possess an exactly alternating microstructure of the silp henylene and siloxane moieties. The materials are completely amorphous with glass transition temperatures between -60 and -86 degrees C. All polymers degrade thermally only above 500 degrees C under both oxidative or inert at mosphere. The char yields at 900 degrees C increase with increasing vinyl c ontent from 30% up to almost 70%. Cross-linking of a small fraction of viny l groups by hydrosilylation gives materials with elastomeric properties. Dy namic mechanical experiments indicate that the bulk of vinyl groups cross-l inks thermally at temperatures above 230 degrees C. Therefore, the temperat ure window for possible applications of these materials as fire-safe elasto mers extends from about -86 degrees C to approximately 230 degrees C.