The vinylic polymerization of norbornenes upon catalysis with Pd2' complexes with norbornylnitrile as ligands is reported. The polynorbornenes (a,,, = lo6) display a set of unique properties including a dense packing in the amorphous state, high glass transition temperatures, large refractive index, low birefringence and significant brittleness. To test the concept that these properties can be traced back to the conformational constraints of the polymer chains, we performed ab initio calculations, semi-empirical quantum mechanical calculations and force-field calculations employing a force field developed by us for polynorbornenes.

Pd(I1) catalysts with nitrilo ligands and BK counter ions give the best results in vinylic polymerization of norbornene. Absolute molecular weight determination of polynorbornene (PN) by means of light scattering and the three-dimensional shape of PN were also investigated. By correlation of molecular weights a, with intrinsic viscosity (Staudinger-index) [q], yield a close to 0.5 exponent for the Mark-Houwink equation with solvents chlorobenzene and cyclohexane at 25 "C expected for polymer molecules with confined conformation. The vinylic polymerization of norbornene with [(CH,CN),Pd] [BF& (I) in nitromethane in the presence of ethylene results in PN with narrow molecular weight distribution. No termination and transfer reactions were found, nor any incorporation of ethylene could be detected.

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