The surface modification of silicon (Si) by polymer has great values for insulation film in microelectronics. Necessarily, the polymer film should be thermally stable to withstand the temperature in packaging process. Herein, we report a thermally stable structure of aromatic amide rings by heat treating the radical grafted poly (methylacrylic acid) (PMAA) film. The initiator, 4-Nitrobenzene diazonium tetrafluoroborate (NBD), can provide -NH2 groups (reduced by -NO2 groups) in the polymer film. Dehydration reaction happens between -COOH groups (from PMAA) and -NH2 groups at 200 degrees C. The products are intramolecular or intermolecular amide rings on benzene ring, with the wettability changing from hydrophilic to hydrophobic. The new structure shows excellent thermal stability after heat treating and the heat-resisting index can be up to 226.6 degrees C. In addition, the polymer film shows the similar dielectric properties with SiO2 that could be used as a refined insulation film in microelectronics or semiconductor industry.