Synthesis, Microstructures, and Properties of Vinylic Poly(alkylnorbornenes)

A series of poly(alkylnorbornene) (PANB) homopolymers with alkyl side chains of 4, 6, and 10 carbons were synthesized using a (1,5-cyclooctadiene)PdMeCl/Ph3P/NaB[(3,5-(CF3)2C6H3)]4 catalyst, and their properties were thoroughly evaluated. In agreement with previous reports for PANBs, glass transition decreases with the alkyl side chain length (Nsc) due to a plasticizing effect of the side chains, which strongly impacts their mechanical response. A sharp transition from a very brittle to very ductile response is observed when Nsc increases from 4 to 10 carbons. Wide-angle X-ray scattering (WAXS) measurements were used to determine that the PANB microstructure consists of molecular bottlebrushes with the distance between adjacent backbones being an increasing function of Nsc. The increase in the side chain length also renders softer melts; hence, the rubbery plateau modulus, measured by linear rheology, is a decreasing function of Nsc. Consequently, the entanglement molecular weight increases with Nsc. The PANB melts are thermorheologically simple materials, as the time–temperature superposition principle holds for the three samples studied. The microstructure evolution of poly(hexyl norbornene) and poly(decyl norbornene) during uniaxial deformation was studied by in situ WAXS measurements. The backbones of these materials align parallel to the deformation direction, as expected, whereas the side chains align with an angle of 30°.