A new catalyst system is developed for regiocontrolled synthesis of poly(2,5-dialkyl-1,4-phenylene oxide)s by oxidative coupling polymerization of 2,5-dialkylphenol. The treatment of the a-benzoin oxime with manganese chloride in methanol under basic condition led to the formation of manganese benziloxime complex in which alpha-benzoin oxime was converted to benziloxime and coordinated to manganese as bidentate ligands. The polymerizations were conducted in toluene using manganese benziloxime complex and dibutylamine in a continuous flow of oxygen, and the structures, properties of the catalyst, and polymers were studied by nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and gel permeation chromatography (GPC). The catalyst showed high regioselectivity and reasonably good yields to afford the poly(2,5-dimethyl-7,4-phenylene oxide)s with 1,4-C-O linkage structure which possessed melting point higher than the poly(p-phenylene sulfide) or type II liquid crystalline polymer. The regioselectivity was enhanced when employing molecular sieves-supported manganese catalyst system at 90 degrees C and the crystallinity of poly(2,5-dimethyl-1,4-phenylene oxide)s was estimated by wide-angle X-ray scattering (WARS) and DSC. The crystallinity was calculated about 23.7% and a heat-reversible melting and crystallization behavior occurred at 327.8 and 306.8 degrees C, respectively. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 1501-1507,2009