Preparation And Catalytic Study Of A Novel Strong Acidic Polymer With Pendant Perfluoroalkylsulfonylimide Groups

As an environment-friendly'green'catalyst, the structure design and study of solid acid is an important task in catalysis domain. One of the methods is to immobilize fluorine substitutional alkyl to organic polymer. It has received continuous interest in recent years, which can enhance the acidity and thermal stability, at the same time decrease the costs.In this paper, long alkyl chain and perfluoalkyl chain were introduced to linear polystyrene and a novel polymer-supported Brφnsted acid, 10- (4'-perfluorobutylsulfonamino sulfonylphenyl) decylpolystyrene (PS-SI), was prepared. It showed strong acidity due to the powerful electron-withdrawing effect of perfluoroalkylsulfonyl group and some unique catalytic properties of the long alkyl chain. The catalytic ability was investigated by the esterifcation in excess water.PS-SI was characterized by FT-IR, 19F solid-state NMR, TGA and SEM. The acidic strength and acid content of PS-SI was tested through Hammitt indicator method and acidimetry, respectively. The results showed that PS-SI had irregular distribution and rough surface, better thermal stability and stronger acidity than commercial sulfonic resins and much higher acid content than perfluorosulfonic resin Nafion. The properties indicate that PS-SI might be a promising catalyst in'green chemistry'.To access the catalytic activity of PS-SI, direct esterifications of equimolar carboxylic acids and alcohols in excess water catalyzed by PS-SI were investigated. The results showed that PS-SI was a new kind of Brφnsted polymer acid of highly catalytic property and could be recycled more than 5 times without any loss of activity. Compared with PPFSI, PS-SI were more active in the esterification reaction with excess water, which showed the long alkyl chain played an important role in such reaction conditions.