Structural Design And Catalytic Application Of Polymer-based Catalytic Nanoreactors

Catalysts play a key role in the production of printing and dyeing auxiliary and dye intermediate.It is extremely important to prepare catalysts with efficient catalytic performance.In homogeneous catalysis,both catalyst and reactants dissolve in the reaction medium,which increases the contact probability,and endows homogeneous catalysts the advantages of high activity and high selectivity.While,homogeneous catalysis also has problems such as difficulties in the separation of catalyst and products.As a stimuli-responsive material,temperature-sensitive polymer can change its properties with the change of temperature.Temperature-sensitive polymer-based nanomicelle as catalyst can not only achieve homogeneous catalysis,but also realize catalyst recovering using the temperature-sensitive property.On the other hand,catalytic nanomicelle containing a temperature-sensitive cross-linked layer in the middle layer is expected to regulate the catalytic reaction rate according to requirement.In addition,incompatible acid-base tandem catalyst can realize one-pot multi-step reactions,reducing consumption in separating and purifying intermediates.The main contents are as follows:（1）Temperature-sensitive polymer was synthesized by reversible addition fragmentation chain transfer（RAFT）polymerization of triethylene glycol methyl ether methacrylate（MEO₂MA）and N-hydroxysuccinimide ester（NMS）monomers.6-Aminohexanoic acid was introduced into the temperature-sensitive polymer using an activated ester strategy to obtain branched carboxyl-containing polymer.The carboxyl groups in the polymer were coordinated with iron ions to obtain a temperature-sensitive iron complex.The temperature-sensitive iron complex was applied as a homogeneous catalyst in the Fenton oxidation system,which improved the catalytic efficiency and reduced the use of iron ions.In the dye degradation experiments,97%and 96%decolorization were achieved for Rhodamine B（Rh B）and methylene blue（MB）within 2 h,respectively.In addition,the catalyst recycling was achieved by heating,centrifugation,and precipitation using the temperature sensitive property.（2）Multi-block copolymers were synthesized from hydrophobic monomer butyl methacrylate（BMA）,allyl methacrylate（AMA）,temperature-sensitive monomer MEO₂MA,and hydrophilic monomer N,N-dimethylacrylamide（DMA）by multiple RAFT polymerization.The polymers containing temperature-sensitive cross-linked layerswerepreparedbythiol-eneclickreaction.Then,2,2,6,6-tetramethylpiperidine-1-oxyl radical（TEMPO）was introduced into the polymers using an activated ester strategy,and polymer-based catalytic nanoreactors containing TEMPO were obtained by self-assembly in water.The size and morphology of the catalytic nanoreactors were characterized by dynamic light scattering（DLS）and transmission electron microscopy（TEM）.At low temperatures（0°C）,the catalytic nanoreactor CL-[D₅₇-b-(M₆₇-co-A₁₁)-b-B₁₈]-TEMPO（8）accomplished 99%efficient selective oxidation of benzyl alcohol with low catalyst loading.At a higher temperature（41°C）,only 56%yield was achieved.The results indicate that the hydrophilcity/hydrophobicity of the temperature-sensitive cross-linked layer of the catalytic nanoreactor can be altered by changing the temperature,which correspondingly can regulate the catalytic rate.（3）Tri-block copolymers were synthesized by RAFT polymerization of BMA,AMA,tert-butyl methacrylate（t BMA）,and poly（ethylene glycol）methyl ether methacrylate（OEGMA）.Base catalyst,acid catalyst,and acid-base tandem catalyst without cross-layer and with cross-layer were prepared by thiol-ene click reaction and post-polymer modification strategies.The structure and molecular weights of the catalysts were characterized by nuclear magnetic resonance hydrogen spectroscopy（¹H NMR）and gel permeation chromatography（GPC）.The sizes and morphologies of the catalysts were characterized by DLS and TEM.The catalytic effects of the above catalytic systems were investigated in the deacetalization-Knoevenagel tandem reaction,respectively.In 5 h,the conversion of the reactant benzaldehyde dimethyl acetal was 98%,and the yield of the final product was 91%under the synergistic effect of acid and base catalysts;the conversion of the reactant benzaldehyde dimethyl acetal was 95%and the yield of the final product was 32%under the acid-base tandem catalysis without cross-linked layer;the conversion of the reactant benzaldehyde dimethyl acetal was 96%under the acid-base tandem catalysis with cross-linked layer,and the yield of the final product was 82%.In whole,the acid-base tandem catalyst with an intermediate cross-linked layer exhibited the best overall efficiency considering the catalyst loading and catalytic efficiency.