To achieve successful integration of low dielectric constant materials with copper lines, it is critical to develop a low dielectric constant material with good mechanical properties. A new high strength spin-on low dielectric constant polymer, poly((m-diethynylbenzene)-co-(triethynylbenzene)), has been developed. Its oligomer showed good solubility, high thermal stability, low moisture pickup, and strong UV absorption. The cured polymer thin film displayed a dielectric constant of 2.7 at 1 MHz and a dielectric breakdown strength larger than 230 V/mu m. It had an extraordinarily high Young's modulus of 16.8 GPa and a hardness of 3.5 GPa. Compared to polyimide, it had stronger adhesion to Si and tantalum. By use of polystyrene as a porogen, a dielectric constant as low as 1.9 was obtained while still maintaining an acceptable high Young's modulus of 7.7 GPa and hardness of 2.0 GPa.