DYNAMICS IN POLYDIMETHYLSILOXANE - THE EFFECT OF SOLUTE POLARITY

The temperature dependent dynamics of polydimethylsiloxane (PDMS) melt s are investigated by measuring orientational relaxation of a dissolve d probe molecule, 2-naphthyltriethoxysilane (NTES) using time resolved fluorescence depolarization. The temperature dependent viscosity of P DMS is also reported for two molecular weights. The measurements of no npolar NTES probe dynamics:are compared to previous measurements on th e polar probe, N-(triethoxysilylpropyl)dansylamide. The activation ene rgies for the orientational relaxation of the two probes are very diff erent. This is discussed in terms of the influence of the polarity of the solutes an the local structure in the melts. The results have impl ications for possible modifications of the physical properties of PDMS materials by using solutes or side groups of varying polarity. The sy nthesis of the NTES probe, which can also be used as a cross-linking r eagent for PDMS, is also described.