Research On Aza-Michael Addition Catalyzed By Quaternary Ammonium Salt And Tertiary Amine Bifunctionalized Polyacrylonitrile Fiber

Heterogeneous catalysts have overcome the drawbacks of small molecular catalysts,such as possible toxicity,difficult recovery and hard reuse,and have become a focus of urgent topic for chemists.Polyacrylonitrile fiber(PANF)has the advantages of high mechanical strength,anti-acid and base,good flexibility,low price and ease to obtain.A large number of cyano and ester groups contained in PANF can be transformed into amido group,carboxyl group and so on by appropriate chemical modification.Therefore,PANF has great potential as a good catalyst support.Compared with other catalyst supports,PANF can be modified much deeper than only on the surface.Due to the swelling of the fiber in the solvent,the small molecular grafted polymer chains in the fiber surface can form special surface microenvironment with solvent and reactant molecules,which renders the fiber catalyst special catalytic activity.A series of bifunctional polyacrylonitrile fibers with adjustable ratio of quaternary ammonium to tertiary amine have been synthesized and characterized by FT-IR,EA,XRD,TGA,mechanical strength,SEM,XPS and water contact angle.The functionalized fibers PAN_PQ-nF successfully constructed a special structure with hydrophobic surface layer and hydrophilic inner layer on the same molecular chain,leading to the high catalyst activities for the aza-Michael addition.The catalytic activity was explored by changing the ratio of quaternary ammonium to tertiary amine.The results showed that the PAN_PQ-1F had the best catalytic activity on the aza-Michael addition reaction of chalcone and aniline when the ratio of quaternary ammonium to tertiary amine was 1:1.More than 99%yield can be obtained at 60°C for 10 h in water with the presence of catalyst PAN_PQ-1F(10 mol%).In addition,the fiber catalyst can still maintain high catalytic activity after being used six times repeatedly under optimal conditions.Besides,the special microenvironment of fiber catalyst PAN_PQ-1F was explored,in which the effect of reactant molecule enrichment and product molecule desorption on the catalytic sites were described;and the mechanism of synergistic catalysis of quaternary ammonium salt and tertiary amine was proposed.