Dynamics of cyclic poly(methylphenylsiloxane)

Fluorescence spectra of cyclic poly(methylphenylsiloxane)s having 3, 4.4 and 9.0 monomelic units, and of the monochromophoric analog methylphenyldimethoxysilane (MS), were measured as a function of temperature in the range 150 to 320 K. Both the low- and the high-temperature limits were reached in this range. The crossover temperature between both limits was thus determined, as well as the activation energy for excimer formation and the excimer binding enthalpy. From measurements of the lifetime of MS as a function of temperature, the rate constant for excimer formation was also determined, and its relationship with the rate constant for rotation through backbone bonds was discussed.