Preparation And Properties Of Triphenylphosphine Functionalized Polymer/Palladium Composite Catalyst

In organic synthesis,triphenylphosphine is an important small molecule tertiary phosphine compound.It is usually used as organic reagents or a ligand for metal complexing catalysts,but it is easy to dissolve in the reaction system and is difficult to separate after the reaction,which will pollute the product.Therefore,it is grafted onto a polymer carrier to form a polymer-supported triphenylphosphine and applied to an organic reaction.After the reaction,it was recycled by filtration or centrifugation,which not only simplified the separation and purification process,but also reduced the production cost and improved the production efficiency.At present,the research on the attachment of triphenylphosphine to macromolecular polymers has attracted more and more attention.The polymer-supported triphenylphosphine has been well used in organic synthesis chemistry,which promotes the development of organic chemical reactions involving small molecular tertiary phosphine compounds as organic reagents.Metal palladium is a catalyst with high catalytic activity and relatively low cost.It is widely used in many organic catalytic reactions such as Suzuki,Heck,Negishi and other C-C coupling reactions.In addition,palladium is also very effective in catalytic reduction of p-nitrophenol,an environmental pollutant.Because some macromolecule polymers are insoluble in the reaction system,the heterogeneous catalysts formed as the support of catalysts have the advantages of easy recovery and utilization,but the catalytic activity is not high.On the contrary,the homogeneous catalyst prepared by using the polymer soluble in the reaction system as catalyst carrier has the advantages of high catalytic efficiency,but the recovery is difficult and the reusability is low.Stimuli-responsive polymer is an intelligent polymer material that can generate a corresponding response behavior according to subtle changes?physical or chemical changes?of the external environment.When the external environment such as temperature,pH,solvent,magnetic field,electric field,ionic strength and illumination changes,the properties of polymer materials will change and produce response behavior.Stimuli-responsive polymer materials play an important role in drug release,environmental protection,bioengineering,and organic catalysis.Thermosensitive polymers are a kind of polymer materials which can change their properties according to the change of external temperature.There is a low critical solution temperature?LCST?in its aqueous solution.When the ambient temperature is below the LCST,the thermosensitive polymer exhibits hydrophilicity and dissolves in water to form a homogeneous system;when the outside temperature is above the LCST,the thermosensitive polymer changes from hydrophilic to hydrophobic and separates from the aqueous phase to form a heterogeneous system.Therefore,the use of thermosensitive polymer as a support for palladium while combining the advantages of a homogeneous catalyst with a heterogeneous catalyst makes the thermosensitive polymer/metal palladium composite catalyst have high catalytic activity,easy recovery,and reusability.In addition,temperature is an important factor affecting the organic catalytic reaction.The change of the external temperature will cause the structure of the thermosensitive polymer to change accordingly.Therefore,the progress of the catalytic reaction can be controlled by controlling the increase or decrease of the reaction temperature.In this paper,a thermosensitive polymer/metal palladium composite catalyst is prepared by complexing a triphenylphosphine functionalized thermosensitive polymer with metal palladium,and is applied to an organic catalytic reaction in an aqueous phase.It not only ensures the high catalytic activity and reusability of the catalyst,but also avoids the use of a large amount of organic solvents,which is in line with the development concept of green environmental protection.A series of thermosensitive polymers with different LCST were synthesized by using N-isopropylacrylamide,oligoethylene glycol methyl ether methacrylate with different molecular weights as thermosensitive monomers,and 4-vinyltriphenylphosphine containing vinyl structural unit as comonomer.Thermosensitive polymer/metal palladium composite catalyst with high catalytic activity and easy recovery was prepared by using thermosensitive polymer as palladium carrier.The structure and properties of the thermosensitive polymer carrier and its metal-palladium composite catalyst were characterized by FTIR,¹H NMR,³¹P NMR,XRD,DSC,TG,TEM,EDS.The prepared catalyst was evaluated by the Suzuki-Miyaura reaction in the aqueous phase and the catalytic reduction reaction of p-nitrophenol,respectively,and various factors affecting the catalytic effect were analyzed.It was found that thermosensitive polymer is an excellent carrier of Pd and the thermosensitive polymer/metal palladium composite catalyst has high catalytic activity and stability,is easy to recover,can be reused for many times,and can control the progress of the reaction with the change of temperature.It is of great significance for the design of intelligent catalyst.In addition,in order to design the thermosensitive polymer carrier with more clear structure,the polymer carrier with triphenylphosphine as ligand was prepared by reversible addition fragmentation chain transfer?RAFT?polymerization,which provided support for the support of metal catalysts.