Solid polymer brush-supported molecular catalysts generally
exhibit
activity comparable to molecular catalysts, but they suffer the problems
of decreased activity with increasing recycled times in reactions.
This study explores the use of polymer brushes with a diblock architecture
to design durable silica-based polymer brush-supported sulfonic acid
catalysts. Two silica-based polymer brush materials, differing in
the amounts of polystyrene (PS) brush, were prepared by first growing
PS brush using copper-catalyzed ARGET SI-ATRP and growing poly(vinylimidazole)
using SI-ATRP. The resulting polymer brushes were then reacted with
1,3-propane sultone and trifluoromethanesulfonic acid to obtain two
solid acid catalysts. For comparison, a solid sulfonic acid without
a PS layer was also prepared. These solid acidic catalysts were applied
to synthesize acylals from aldehydes and acetic anhydride. The polymer
brush-supported acids demonstrated superior activity compared with
the molecular catalyst. Notably, the catalyst with PS protection could
be recycled 15 times (yield ≥95%) without a decrease in activity;
in contrast, the yield of the catalyst without PS protection decreased
to 35% in the 10th run. Thermogravimetric analysis indicated 3% loss
of materials for the catalyst with the PS layer and 9.5% loss for
the catalyst without the PS layer, after the specified numbers of
runs. Polymer brush protection probably finds more applications in
the design of more durable solid-based polymer brush-supported molecular
catalysts.