Radical Reactivity of Hydrovinylsilanes:  Homooligomers

Diphenylvinylsilane ( 1 ) undergoes oligomerization when initiated by azobis(isobutyronitrile) or peroxide initiators (benzoyl peroxide, di- tert -butyl peroxide, dicumyl peroxide). With the exception of the reaction with di- tert -butyl peroxide, the efficiency of the radical reactions is very low: 15% starting material was recovered even with 1 equiv of added initiator. The Si vinyl groups are consumed preferentially to the Si H groups. The magnitude of the relative rates of consumption depends upon the reaction conditions and the nature of the initiator. At lower temperatures (80 °C), k Si CH CH2 / k Si H ≈ 2, which decreases to about 1.2 at elevated temperatures (160 °C). The relative radical reactivities of the two functional groups are discussed. The residual Si H moieties can be subsequently coupled by hydrosilation with alkynes or vinylsilicones to form star silicones.