DYNAMIC STUDIES OF THE MOLECULAR RELAXATIONS AND INTERACTIONS IN MICROCOMPOSITES PREPARED BY INSITU POLYMERIZATION OF SILICON ALKOXIDES

In-situ polymerization of silicon alkoxide was used to prepare composites of silicon dioxide and poly(vinyl acetate) (PVAc). The local environment of the PVAc chains was probed using FTIR, dielectric, and dynamic mechanical spectroscopy. Dielectric relaxation master curves were prepared, and the dielectric data were fit to the empirical Kohlrausch-Williams-Watts function (KWW). The results showed that beta decreased with increasing sol-gel concentration, indicating that there is a broadening in the distribution of relaxation times for PVAc chains. The results suggest that there exists an interfacial region in the composites where the mobility of the PVAc is reduced by the interactions with the silicate network. In addition, at high concentrations of tetraethoxysilane (TEOS) it was not possible to shift the data because of a breakdown of time-temperature superposition. Further, at these concentrations a plateau region above T(g) was observed by dynamic mechanical analysis. The results show that the silicate network inhibits the relaxation of at least a portion of the PVAc chains, and it is believed that the plateau is a manifestation of the PVAc chains that are entrapped in a continuous silicate network and of the nature of the network itself It was also shown that the distribution of relaxation times narrows as the cure temperature increases. In addition, as the composite is cured, the amount of hydrogen bonding between the PVAc and the silicate network decreases. This is presumably due to further condensation of the silicate and the proportional decrease in the amount of available silanol groups.