NMR spin-spin relaxation studies of silicate-filled low molecular weight poly(dimethylsiloxane)s

Nuclear magnetic resonance (NMR) spin-spin relaxation measurements were used to investigate the mobility of poly(dimethylsiloxane) (PDMS) polymers, below the molecular entanglement point, when mixed with trimethylsilyl-treated polysilicate nanoparticles. The results showed that a high molecular weight polysilicate caused a dramatic reduction in the overall PDMS chain mobility at all concentrations. The relaxation decays were deconvoluted into multiple exponential decays using nonlinear least squares and the DISCRETE algorithm. The components of these decays were associated qualitatively with adsorbed and nonadsorbed polymer segments. When compared with differential scanning calorimetry measurements, the reduction in the mobility of the PDMS chains as seen in the NMR experiments corresponded to a shift in the glass transition to higher temperatures, a decrease in the specific heat increment at the glass transition, and a loss in the ability of the polymer to crystallize at high concentrations of polysilicate.