Research On The Design,Preparation And Application Of Polymer Brush-based Catalyst Carrier

Catalysis plays a vital role in chemical engineering including the preparation of dyes and printing and dyeing auxiliaries.How to improve the efficiency of catalytic reactions is a current research hotspot.Homogeneous catalysis and heterogeneous catalysis are two important directions in the field of catalysis.In homogeneous catalysis,the catalyst and the substrate are fully dissolved in the solvent,and the reaction selectivity is high.However,due to the thorough mixing of the entire system,it is difficult to recover the catalyst.On the contrary,the catalyst in the heterogeneous catalytic reaction is easy to recover,but the catalytic efficiency is low.The emergence of the micellar nanoreactor perfectly combines the advantages,using the small size effect and confinement effect of its special structure to achieve highly efficient chemical conversion,and can use its macromolecular characteristics for catalyst recovery and reuse.The micellar nanoreactor is usually prepared by self-assembly of hundreds or even thousands of amphiphilic block copolymer chains.The preparation is simple,the dispersion in the water phase is good,and the structure is easy to adjust.However,its stability is poor because the structure is greatly affected by temperature and concentration.Bottlebrush polymer is a kind of polymer with high-density grafted side chains on the linear polymer main chain.Nanoreactors from bottlebrush polymers have greatly enhanced structural stability compared with the self-assembly of traditional amphiphilic copolymers.Because of this,the thesis is devoted to the development of bottlebrush polymer-based catalyst supports,and the construction of catalytic nanoreactors with high catalytic efficiency and stable structure through self-assembling in water.The main research contents and results are as follows:（1）In this study,the hydrophobic copolymer NB-P（BEMA-co-MMA）containing a terminal norbornene（NB）group was prepared by reversible addition fragmentation chain transfer（RAFT）polymerization of methyl methacrylate（MMA）and bromoethyl methacrylate（BEMA）firstly.Next,the water soluble polymer NB-PEG was synthesized by the condensation reaction of polyethylene glycol monomethyl ether（PEG,Mn=5000）and 5-norbornene-2-carboxylic acid.Then,the 3^rd Grubbs catalyst was used to catalyze the ring-opening metathesis polymerization（ROMP）of the hydrophilic and hydrophobic segments to form amphiphilic polymer brushes.Finally,different types of catalysts such as triethylenediamine（DABCO）and 4-dimethylaminopyridine（DMAP）were introduced by simple nucleophilic substitution of Br on the halogenated monomer BEMA,and the micellar catalytic nanoreactor was formed by self-assembly in water.The structure and molecular weights of the polymers were characterized by Nuclear Magnetic Resonance（NMR）and Gel Permeation Chromatography（GPC）;the size and morphology of the micellar nanoreactor were characterized by Dynamic Light Scattering（DLS）and Transmission Electron Microscopy（TEM）.The DABCO-functionalized nanoreactor can efficiently catalyze the Knoevenagel condensation reaction in water.For different substrates,more than 93%yields were achieved within 1 h with 5 mol%catalyst loading.The DMAP-functionalized nanoreactor can efficiently catalyze the acylation reaction of alcohol in water.For different alcohols,more than 97%conversion could be obtained within 1 h with 5 mol%catalyst loading.All reactions use water as the medium,the reaction conditions are mild,and the catalyst can be recycled and reused.（2）Further,this study designed and prepared a kind of polymer brush-based catalyst carrier suitable for tandem catalysis,and discussed its application in acid-base tandem catalysis.First,a hydrophobic polymer with NB at the end（NB-PMMA）,a hydrophilic polymer with a tert-butyl protecting group poly-tert-Butyl acrylate（NB-Pt BA）,and a functional monomer（NB-NHS）with N-hydroxysuccinimide（NHS）activated ester were synthesized.Then,the 3^rd generation Grubbs catalyst catalyzed the ring-opening metathesis polymerization（ROMP）of above 3 NB monomers to form the bottlebrush polymer PMMA-b-NHS-b-Pt BA.Finally,the activated ester functionalization strategy was used to load DABCO onto the polymer to obtain basic catalytic sites.The acidic catalytic sites were obtained by deprotection of tert-butyl acrylate,followed by self-assembling in water to achieve the catalytic nanoreactor.We preliminarily studied the Deacetalization-Knoevenagel tandem reaction by the developed nanoreactor.The results showed that all benzaldehyde dimethyl acetal can be completely converted within 3 h,and all the benzaldehydes produced undergo Knoevenagel condensation reaction to provide the corresponding tandem catalytic products within 24 h.