Preparation, Characterization And Catalytic Activity Of Cross-linked Polystyrene With Pendant Perfluoroalkylsulfonylimide Groups

The general sulfonated polymer has been widely applied as a kind multifunctional polymer in industry. It can not be employed in some reactions in catalysis domain because of its poor chemical stability and low acid strength (H0 = -3), which only use safely below 120℃and lose sulfonic group above 140～150℃. So it's necessary to develop novel strong Br?nsted acid polymer that can tolerate high temperature. But most of the researches were mainly focused on the investigation of perfluorinated sulfonated polmer or partly fluorinated sulfonated polmer in passed two decades. As a kind of outstanding weakly coordinating anions, perfluoroalkylsulfonylimide anions have been receiving continuous interests and extensively studied in recent years. However, there is no report on the polymer containing side perfluorosulfonylimide groups in catalysis domain. In this paper, crosslinked polystyrene was used as polymer support. The SO₂-NH-SO₂ units were introduced to the polymer and expected to show 'super'acidities due to the powerful electron-withdrawing effect of perfluoroalkylsulfonyl group (-SO₂CF₃, -SO₂CF₂CF₂CF₂CF₃). On the other hand, some of Lewis acids were immobilized onto the novel strongly acid polymer (PPFSI) and the preparation methods and property of the catalysts were investigated, too. In order to evaluate the physical properties and hole structure of the PPFSI, the thermal stability of the PPFSI was investigated by the thermogravimetric analysis and variable temperature infrared spectrum. The hole structure variety of the polymer via fluorination was analysed by SEM and the acid strength of the PPFSI was characterized by the Hammett indicator method. Results showed that the PPFSI was a kind strongly acid polymer that was tolerant of 170℃temperature. The direct esterification of carboxylic acids and alcohols was chosen to be a model reaction in 10 mol% amount of the PPFSI. The PPFSI could be reused more than five times successively at 120-125℃without any loss of its activity and showed to be higher catalytic activity compared with other solid-state acids, which also improved recycling stability and strong Br?nsted acidity in experiments. Due to the special characteristic (thermal stability,hydrophobic property and strong acidity) of the PPFSI compared with sulfonated polymer, its catalytic activity was investigated in aqueous media, too. We also increased carbon-fluorine chain length to strengthen the hydrophobic nature of the PPFSI, and discussed the reaction conditions, hydrophobic property and the chain-length effect on the catalytic activity in aqueous media. The results paved a way to the further study. In addition, the PPFSI was used as the support polymer, on which Lewis acid was immobilized in this paper. It was found that the reaction system, swelling reagent, reaction temperature and the configuration block played an important role in the load amount and support extent of the Lewis catalysts.