(1)H/(29)Si cross-polarization NMR experiments of silica-reinforced polydimethylsiloxane elastomers: probing the...

Polydimethylsiloxane (PDMS) elastomers reinforced with fumed silica exhibit unusual strength characteristics that are necessary for their designed applications. The microscopic details of the surface interaction between the polymer and silica are not well characterized. (1)H/(29)Si cross-polarization (cp) experiments are used to characterize cured and uncured samples of Dow Corning silastic 745. Changes to the cp dynamics upon curing are evident by the variation in peak intensities in the variable contact-time spectra of the two samples. Estimates of the cp relaxation parameters are reported for the cured sample. Additional information can be obtained by expanding the (1)H/(29)Si cp to a two-dimensional heteronuclear correlation experiment. Dramatic differences between the cured and uncured (1)H/(29)Si HetCor spectra are observed that are not visible in the 1D spectra. These changes can be rationalized as a dehydration of the silica surface and an increased hardening of the polymer after the curing process. Furthermore, isolation of the NMR signal corresponding to nuclei at or near the polymer-filler interface may be achieved in the 2D (1)H/(29)Si HetCor spectrum.