Homopolymerization and copolymerization of styrene and norbornene with Ni-based/MAO catalysts
Résumé
The homopolymerization of styrene (Sty) and norbornene (NBE) was investigated in the presence of the nickel stearate (NiSt)/methylaluminoxane (MAO) catalytic system in toluene and in chlorobenzene at 20 8C. The fully saturated structure of polynorbornene indicates that the two monomers polymerize by an ethylenic type addition reaction. The synthesis of true copolymers shows that one type of active species is operating for the two monomers. Determination of reactivity ratios (r NBE = 20.8 and r Sty = 0.02) indicates a much higher reactivity of NBE, which is interpreted by a coordination mechanism. The styrene-norbornene copolymers exhibit glass transition temperatures (T g) which range from 100 8C to 320 8C and follow Kovacs' law. The absence of crystallinity and the homogeneous repartition of monomer units along the chains yield highly transparent materials of high thermal stability.