Preparation And Catalytic Properties Of Polysiloxane Loaded Metal-organic Framework Composites

Knoevenagel condensation reaction is one of the effective ways to prepare C=C,and the reaction products are widely used in various organic reactions.In the past century,many studies have been carried out on this reaction,and the catalysts are mainly primary amine and secondary amine salt.However,due to many by-products and difficult separation,the effect is not good.In order to better obtain olefin compounds,it is urgent to develop environmentally friendly heterogeneous catalysts.In recent years,researchers have tried to use metal-organic frameworks（MOFs）as catalysts.Although they are easy to separate,the yield is still lower than expected.As an important branch of functional polymers,polymer-supported catalysts have high activity,good stability,easy separation,purification and recycling.In this paper,the preparation of polysiloxane supported metal-organic framework mil-101（Cr）composites based on amino functionalization（MIL-101（Cr）/pr-NH₂-PSi OA）,and the catalytic Knoevenagel condensation reaction of benzaldehyde and malononitrile was used as a probe experiment to explore the properties of the composites.The research contents are as follows:（1）A kind of side chain amino-modified polysiloxane（pr-NH₂-PSi OA）was successfully synthesized by polycondensation reaction using measuredγ-aminopropylmethyldiethoxysilane（APDES）and dimethyldimethoxysilane（DMDMS）as raw materials,potassium hydroxide as catalyst,and hexamethyldisiloxane（MM）as capping agent.A series of characterization instruments were used to investigate the physical and chemical properties of pr-NH₂-PSi OA.The molecular structure of pr-NH₂-PSi OA was determined by Nuclear Magnetic Resonance and Fourier Transform Infrared spectroscopy.The molecular weight,viscosity and amine value of pr-NH₂-PSi OA were investigated by Gel Permeation Chromatography,rotary viscometer and Hydrochloric acid titration.（2）A series of polymer-loaded heterogeneous composites x MIL-101（Cr）/pr-NH₂-PSi OA were prepared by using pr-NH₂-PSi OA,which was self-synthesized in the laboratory,as the carrier and MIL-101（Cr）as the active site,and the unsaturated metal sites in the MOFs were ligand-bonded to the amino groups by post-synthetic modification techniques.The physicochemical properties of x MIL-101（Cr）/pr-NH₂-PSi OA composites were also characterized with the help of various characterization instruments:the compositional structure of the composites was characterized by Fourier Transform Infrared;the crystalline shape and physical appearance of the composites were investigated by wide-angle X-ray Powder Diffraction;the composition and thermal stability of the composites were investigated by Thermogravimetric analysis;the elemental composition of the surface of the composites and the atomic valence state were obtained by X-ray Photoelectron Spectroscopy;the hydrophobicity of the composites was compared by water Contact Angle test;the surface morphology of the composites was observed and analyzed by ultra-high resolution thermal field emission Scanning Electron Microscopy;the specific surface area,pore size and their distribution of the composites were fitted by nitrogen isothermal adsorption and desorption tests.（3）Taking the Knoevenagel condensation reaction of benzaldehyde and its derivatives with malononitrile as the model reaction,the effects of the molar ratio of the reaction substrate,the loading amount of MIL-101（Cr）in the composite,the type of solvent,the reaction temperature,the amount and type of catalyst and the number of cycles on the catalytic performance were investigated by single factor experiment.The structural formula of condensation product was determined by NMR technique,and the yield of condensation reaction was calculated by gas chromatography.Finally,the cyclic performance of 0.3MIL-101（Cr）/pr-NH₂-PSi OA composite was investigated.