A polymer-forming monomer, dimethylphenol, was incorporated into neat asphalt at 180 degrees C and tensile strength and rutting resistance of the asphalt improved dramatically. We found that polymerization occurred autonomously in the asphalt with some asphalt components and oxygen molecules in the air. The polymer produced was poly(phenylene oxide) (PPO), and its components were vanadium and its oxides. An increase in both the number and weight average molecular weights of PPO indicated a progress of polymerization. An increase in molecular weight contributed to an increase in the melting temperature, tensile strength, and rutting resistance parameter. NMR and IR spectra illustrate the corresponding peaks of PPO. DSC data reveals that the polymer has a melting temperature of 223 degrees C, confirming the presence of PPO. Moreover, the asphalt containing a purported PPO displayed a 35.4% crystallinity, compared to the amorphous structure of asphalt. POLYM. ENG. SCI., 55:1128-1132, 2015. (c) 2014 Society of Plastics Engineers