Elucidating the Stabilizing Effect of a Surface Polymer Layer in Grafted Ti(IV)‐Calixarene Complexes on Silica

We investigate the stabilizing effect of a styrenic surface‐polymer layer, which was previously shown to increase the robustness of grafted Ti(IV)‐calixarene on silica catalysts under harsh liquid‐phase environments (leading to extensive leaching in the absence of the polymer). This was performed using a combination of 13 C MAS NMR spectroscopy with isotopically‐labeled calixarene sites to confirm this leaching of sites previously inferred solely on the basis of gravimetric data, as well as leaching experiments involving sequential Ti(IV)‐calixarene grafting both before and after surface polymerization. The latter demonstrate protection of grafted Ti(IV)‐calixarenes added prior to but not after surface polymerization, demonstrating a lack of observed surface‐polymer reorganization to affect protection to all sites. Our data are consistent with a mechanism involving localized polymer interaction with grafted Ti(IV)‐calixarene sites, rather than a gatekeeping mechanism in which polymer acts to effectively entrap an ensemble of grafted calixarenes in a partially plugged (by polymer) pore. This mechanism is supported by the polymer imparting hydrophobicity, as verified with adsorption of Reichardt's dye, with this hydrophobicity slightly affecting the edge energy of the ligand‐to‐metal‐charge‐transfer band of the grafted Ti(IV)‐calixarene sites.