Synthesis and characterization of substituted polynorbornene derivatives

This paper describes palladium (II) catalyst based synthesis and detailed characterization of vinyl-type polynorbornenes (PNBs) with bulky phenyl, adamantane, or norbornane substituents linked by ester, ether, or alkyl bridges. The structure-property relationships of the substituted PNBs were investigated concerning the thermal stability, glass transition temperature, wide-angle X-ray scattering (WAXS) patterns, mechanical properties, and dielectric characteristics. PNBs with phenyl substituted pendant groups improved the solubility and film forming properties due to aromatic-aromatic interactions. The substituted PNBs exhibited good thermal and thermo-mechanical properties with thermal decomposition temperature (Td,5%) above 300 °C and glass transition temperature in the range of 134-325 °C. WAXS studies revealed the presence of local nano-scale order in the noncrystalline state, especially in ester bridged adamantane and norbornane substituted polymers, probably due to the steric packing requirements of bulky side groups coupled with dipolar interactions. Nanoindentation results showed high modulus (6.5-7.9 GPa) and hardness (0.11-0.38 GPa) for PNBs with diester adamantane and norbornane substituted polymers. Excellent dielectric properties with a dielectric constant (ɛ) of 2.5 and a dielectric loss tangent (tan δ) of 0.0005 were measured for poly [2-(4-phenylbutyl)-5-norbornene] at 1 GHz, rendering it very attractive for interconnect dielectric films in high-frequency electronic devices.