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含有全氟烷基磺酰亚胺基侧链聚苯乙烯的合成﹑表征及其催化研究

Preparation, Characterization and Catalytic Activity of Cross-linked Polystyrene with Pendant Perfluoroalkylsulfonylimide Groups

【作者】 肖杰展

【导师】 聂进;

【作者基本信息】 华中科技大学 , 有机化学, 2005, 硕士

【摘要】 普通的磺酸树脂作为一种多功能高分子已获得广泛的应用,在催化领域由于其热稳定性较差,使用温度仅限120℃以下,在140-150℃会失去磺酸基团而失活; 同时由于其酸强度偏低(H0 = -3),在一些反应的应用上受到了限制,因此开发新型、耐高温的强Br?nsted 酸高分子一直是人们关注的课题。但是,目前开发的主要还是全氟化的或部分氟化的磺酸树脂。近年来,全氟磺酰亚胺类阴离子作为一类重要的弱配位有机阴离子,受到广泛关注并开展了深入的研究。然而,有关新型含氟氮超酸树脂用于催化方面还未见报道。本文以交联的聚苯乙烯为高分子载体,通过一定的手段将全氟磺酰亚胺基团悬挂到高分子载体上,形成一种氮超酸式的离域结构而显示出很强的酸性,成为了一种新的强酸高分子(PPFSI); 同时,本文还就一些Lewis 酸在PPFSI 上的负载形式和方法进行了一些探索。为了评价PPFSI 的物性和结构,用热重分析和可变温红外测试了热稳定性、用环境扫描电镜分析了氟化高分子孔洞结构的变化、用Hammett 指示剂蒸汽吸附法测量了酸强度。结果表明,这种悬有全氟磺酰亚胺基团的聚苯乙烯(PPFSI)是一种能耐170℃高温的强酸高分子。同时,我们以酯化为模型反应,在10 mol% PPFSI 用量下考察了各种羧酸和醇的酯化反应。在120~125℃高温条件下,循环催化5 次未发现PPFSI催化活性的降低,表明PPFSI 是一种有效的、能耐较高温度的Br(?)nsted 酸催化剂。由于氟化高分子相对于磺化高分子的特殊性(热稳定性﹑疏水性和强酸性),本文也在水相体系中考察了PPFSI 的催化活性。并延长碳氟链,增加疏水性,探讨了在水相催化体系中碳氟链长的变化﹑疏水性﹑反应比例以及温度等对催化活性的影响。初步证实了反应物和催化剂形成的疏水环境推动反应平衡进行的原理,这为后面设计更为有效的水相体系的催化剂提供了理论指导。另外,本文也在PPFSI 上进行了一些Lewis 酸负载的探索和尝试,但我们发现反应体系﹑溶涨试剂﹑反应温度以及与金属阳离子成键的阴离子位阻都与负载量和负载牢固的程度有着很大的关系,这就为后面开展Lewis 酸负载的工作打下了很好的基础。

【Abstract】 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.

  • 【分类号】O631.3
  • 【被引频次】4
  • 【下载频次】174
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