Cyclic olefin polymerization and relationships between addition and ring opening metathesis polymerization

Results of our work concerning: (i) the elucidation of the role of the ionic species [CPTiCH]+[Cl · MAO] and of precursors of alkylidene CpTi=CH species in addition alkene polymerization, (ii) the synthetical strategies for converting the living active titanacyclobutanes into ?-titanocene complexes, and (iii) the evidence for the synthesis of polyethylene polynorbornene di-block copolymer are briefly summarized. C NMR spectra of ethylene-norbornene copolymers, prepared with addition catalysts based on ansa-zirconocenes and methylaluminoxane as cocatalyst, and assignments of comohomer pentads in ethylene-norbornene (EN) copolymers are reported.