Logarithmic thermal degradation of a silicone resin in air

The weight‐loss of a methyl‐phenyl silicone resin was determined over the temperature range from 135 to 240°C. and up to approximately 10% volatilization. Weight‐fraction volatilized varied linearly with the logarithm of time. The history of such logarithmic processes is reviewed briefly. The empirical rate‐equation is discussed in terms of the data. On the basis of a surface‐removal experiment, and on the basis of the chemistry of the degradation, a mechanism of Fickian diffusion is proposed, wherein the diffusion coefficient varies exponentially as the degree of crosslinking and shrinkage, while the concentration gradient of volatilizable molecules remains constant.