Step of Substrate to Polymer-Cu Catalysts

As Table 15 shows, the rate constant k of the polymer catalyst system is smaller than that of the monomeric pyridine-Cu catalyst, because of the bulky polymer ligand obstructing the coordination of the substrate to the catalyst153.  

The formation constant (Ka) of the substrate-coordinated complex, polymer-ligand-Cu(lI)-substrate, was kinetically determined for the dimerization of XOH 

XOH = 2,6-dimethylphenol, oligo-PO = oligo(2,6-diinethylphenyleneoxide)(DP 24), PDA = partially diethylaminomethylated poly(styrene), benzene solvent, 30 °C. Ka and k2 are formation constant and rate constant in Eq. (21). 

On the other hand, an attempt to accelerate the step of coordination of the substrate to the Cu catalyst was successful because it used the hydrophobic domain of the polymer ligand156 That was the oxidation catalyzed by polymer-Cu complexes in a dilute aqueous solution of phenol, which occurred slowly. The substrate was concentrated in the domain of the polymer catalyst and was effectively catalyzed by Cu in the domain. A relationship was found to exist between the equilibrium constant (Ka) for the adsorption of phenol on the polymer ligand and the catalytic activity (V) of the polymer-ligand-Cu complex for various polymer ligands K a = 0.21 1/mol and V = 1(T6 mol/1 min for QPVP, K a = 26 and V = 1(T4 for PVP, K a = 52 and V = 10-4 for the copolymer of styrene and 4-vinylpyridine (PSP) (styrene content 20%), and K a = 109 and V = 10-3 for PSP (styrene content 40%). The V value was proportional to the Ka value, and both Ka and V increased with the hydrophobicity of the polymer ligand. The oxidation rate catalyzed by the polymer-Cu complex in aqueous solutions depended on the adsorption capacity of the polymer domain. 

This hydrophobic polymer-Cu catalyst was utilized to remove phenol from an aqueous solution157. A dilute aqueous solution of phenol was made to flow through the column packed with the PSP-Cu resin. Phenol was adsorbed on the polymer and furthermore oxidized to insoluble polymeric compounds in the column. 

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