Controllable Preparation Of Polystyrene-supported Acid-base Cooperative Catalytic Systems And Their Applications In Aldol Condensation

The intermolecular carbon-carbon bonds that can be created by the aldol condensation can be used to make the commonly used aldehyde/ketone and α,β-unsaturated aldehyde/ketone.The development of efficient catalysts for aldol condensation is one of the hot research topics.The creation of supported acid-base cooperative catalysts and its applications have drawn a lot of interest since they are inspired by the acid-base cooperative behaviors of aldolase.By utilizing the synergistic impact between the acid and base functional groups,an acid-base cooperative catalytic system can considerably increase the catalytic activity during catalytic processes.Meanwhile,the supported catalytic system not only provides excellent catalytic activity,but also greatly improves the stability and reusability of the catalyst.Among the varies of supporting materials,polymers are favored by researchers for their advantages such as highly controllable and flexible chain segments.Based on this,a controlled preparation method of polystyrene-supported acid-base cooperative catalytic systems was developed in this thesis,which first grafted acid/base functional groups onto polystyrene in a controlled manner and then prepared acid/base functionalized polystyrene into spherical and uniform-sized nanoparticles under mild and controlled conditions using nanoprecipitation.These nanoparticles are abundant in acid/base functional groups,which can efficiently and synergistically catalyze the aldol condensation.Initially,the functional groups for the acid and base were determined to be catechol and benzylamine.Benzylamine-containing polystyrene and catechol-containing polystyrene with different compositions were synthesized by varying the feed ratio of styrene to functionalized styrene,which can be used for nanoprecipitation.Due to the hydrophobicity of polystyrene chains,the transformation process from linear polymers to spherical nanoparticles not only builds a hydrophobic microenvironment but also achieves the spatial proximity of catechol and benzylamine groups,thus facilitating the realization of synergistic catalysis.In addition,we investigated the effect of polymer composition on catalytic performance and the reusability performance of cooperative catalytic systems to elucidate their structure-activity relationships.Our results demonstrate that this polymer supporting strategy can build acid-base cooperative catalytic systems more efficiently and controllably.To further improve the synergistic catalytic effect and investigate the importance of spatial proximity and hydrogen bonding effects on synergistic catalysis,we optimized the polymer structure by modifying benzylamine-containing polystyrene to synthesize thiourea-containing polystyrene,whose thiourea groups have been shown to have strong potential to form hydrogen bonds and provide more powerful immobilization.Moreover,we used click chemistry to synthesize imidazolidinone-containing polystyrene.The polystyrene-supported imidazolidinone and thiourea acid-base cooperative catalytic systems showed higher and more stable synergistic catalytic performance for aldol condensation than the polystyrene-supported benzylamine and catechol acid-base cooperative catalytic systems,probably due to the greater stability of the acid-base pairs composed of imidazolidinone and thiourea.In order to investigate the relationship between catalytic activity/selectivity and structure/composition of this catalytic system,we designed Knoevenagel condensation to verify the important role of thiourea-containing polystyrene in the polystyrene-supported acid-base cooperative catalytic systems,which achieved selective catalysis of carbonyl compounds.In summary,this thesis provides a controllable preparation method for polystyrenesupported acid-base cooperative catalytic systems.We selected benzylamine/catechol and imidazolidinone/thiourea as acid/base functional groups,which realized the controllable preparation of polystyrene-supported acid-base cooperative catalytic systems by using nanoprecipitation.Our results show that benzylamine/catechol and imidazolidinone/thiourea can be used as acid/base functional groups to achieve the controlled construction of polystyrene-supported acid-base cooperative catalytic systems and show excellent catalytic performance for aldol condensation in water.The controllable preparation and modulation strategy reported in this thesis is expected to provide a reference for the preparation of polystyrene-supported acid-base cooperative catalytic systems.