Poly(N-vinylimidazole) (PVI) was grafted onto magnetic Fe3O4 nanoparticles through siloxane bonds to produce PVI-grafted Fe3O4 nanoparticles (shortened as Fe3O4-g-PVI). The amount of imidazolyl groups in Fe3O4-g-PVI was estimated to be 1.16 mmol/g by elemental analysis and thermal gravimetric analysis. The Fe3O4-g-PVI coordinated with Cu(II) to form the immobilized Cu(II)-PVI complex. The stoichiometric ratio between imidazolyl groups in Fe3O4-g-PVI and Cu(II) was found to be 4 and the complex formation constant (K) was calculated to be 5.6 x 10(14) mol-4 L4. The immobilized Cu(II)-PVI complex was employed to catalyze the oxidative polymerization of 2,6-dimethylphenol (DMP) in water and showed excellent C?O/C?C selectivity to form PPO. After polymerization, the immobilized Cu(II)-PVI complex catalyst was collected by an external magnetic field and reused in the next run with additional immobilized catalyst and copper ions. After three runs of oxidative polymerization of DMP, the recovery rate of the immobilized Cu(II)-PVI catalyst was above 95% and the yield of PPO maintained as high as 79.2% with the addition of supplementary catalysts. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012