Enhanced Recyclability of Polymer Brush-Supported Sulfonic Acid with Diblock Architecture

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.