Solid-state nuclear magnetic resonance studies of vinyl polymer/silica colloidal nanocomposite particles.

Solid-state nuclear magnetic resonance (NMR) has been used to characterize the interface between the organic and inorganic components of "core-shell" colloidal nanocomposite particles synthesized by in situ aqueous (co)polymerization of styrene and/or n-butyl acrylate in the presence of a glycerol-functionalized silica sol. Polymer protons are in close proximity (<5 A) to surface silanol sites in all the nanocomposites studied, indicating that either styrene or n-butyl side groups extend between the glycerol-functional silane molecules toward the surface of the silica particles. For the poly(styrene-co-n-butyl acrylate)/silica nanocomposite n-butyl acrylate residues are located closer to the surface of the silica particle than styrene residues, suggesting a specific interaction between the former and the glycerol-functionalized silica surface. The most likely explanation is a hydrogen bond between the ester carbonyl and the glycerol groups, although this cannot be observed directly. For the Bindzil CC40 glycerol-functionalized silica sol the relative intensities of (29)Si NMR lines corresponding to T and Q(3) environments imply that there are approximately twice as many unreacted silanol groups on the silica surface as attached silane molecules.