A propargyl ether-functionalized poly(m-phenylene) (PE-PMP) is reported here. This polymer exhibits good solubility and film-forming ability. After postpolymerization at high temperature, the polymer transforms to a cross-linked network, which shows high thermostability with a 5% weight loss temperature at 471 degrees C and a char yield of 67% at 1000 degrees C under N-2. Thermo-mechanical analysis (TMA) reveals that the cured polymer shows an average linear coefficient of thermal expansion (CTE) of 30.6 ppm degrees C-1 ranging from 30 to 300 degrees C and a glass transition temperature (T-g) near 330 degrees C. Moreover, even at temperatures up to 300 degrees C, the cured polymer possesses a storage modulus exceeding 4.0 GPa. These data are superior to those of the commercial epoxy and novolac resins and polyimides. Furthermore, the cured polymer film has good mechanical properties with hardness, Young's modulus and a bonding strength to a silicon wafer of 1.22, 9.44 and 0.78 GPa, respectively. The cured polymer film also shows good dielectric properties with an average dielectric constant of 2.93 in a range of frequencies from 2 MHz to 30 MHz. Such results suggest that the polymer is a useful precursor for preparation of insulating materials with high modulus and Tg in the microelectronics industry.