Reorientational motion of a crosshyphen;link junction in a poly(dimethylsiloxane) network measured by timehyphen;resolved fluorescence depolarization

摘要

The reorientational dynamics of a crosshyphen;link junction in poly(dimethylsiloxane) networks, measured by the fluorescence anisotropy decay of a chromophore tagged to the crosshyphen;link, have been investigated over a range of temperatures fromTg+75 toTg+150. The probe chromophore, 1hyphen;dimethylaminohyphen;5hyphen;sulfonylnaphthalene amide (dansyl amide), is pendant to a trifunctional silane that acts as a crosshyphen;linking molecule. In cyclohexanol, the fluorescence anisotropy decay is in agreement with Debyendash;Stokesndash;Einstein hydrodynamic theory (rotational diffusion) demonstrating that the crosshyphen;linker can be used as a probe of orientational relaxation. The fluorescence anisotropy decays at a rapid rate in an endhyphen;linked poly(dimethyl siloxane) network reflecting fast reorientational motion of the crosshyphen;link junction. This reorientation appears diffusive and has a temperature dependence in accord with the Williamsndash;Landelndash;Ferry equation. A model is proposed that suggests that reorientation and translational motion of the crosshyphen;link occur simultaneously and are both coupled to fluctuations of the polymer chain ends.