Effect of crosslink density on the refractive index of a polysiloxane network based on 2,4,6,8‐tetramethyl‐2,4,6, 8‐tetravinylcyclotetrasiloxane

Crosslink density is one of the factors which dictate the optical and mechanical properties of silicone‐based polymers. A series of hydrosilyl‐terminated polydimethylsiloxane cured with 2,4,6,8‐tetramethyl‐2,4,6,8‐tetravinyl cyclotetrasiloxane was prepared to form a crosslink network. They were clear gel forms whose elastomeric features were dependent on the end‐capper concentration, 1,1,3,3‐tetramethyldisiloxane, employed during their synthesis. The siloxane‐based polymers displayed excellent thermal stability whose decomposition temperature was around 480 °C. The refractive index was in the range 1.410–1.425. It was found that the refractive index is dependent on the crosslink density of the network. The effect of fractional free volume and ‘densification’ of the network was elucidated and found to contribute to this dependence. The Lorentz–Lorenz model was used to integrate these observations. © 2012 Society of Chemical Industry