It has been reported that the polymerization of 5-methylenebicyclo[2.2.l]hept-2ene (1) is catalysed by EtAlCl, ') at -130°C, by A1Br3 2, at -78°C and by WC&/R,Sn (R = Bu, Ph)" at ambient temperature. IR and 'H NMR spectra indicate that the product obtained with the first two catalysts has no unsaturation. It is, therefore, thought to have structure 2*) and to be formed by a cationic mechanism, involving a transannular cyclopolymerization. On the other hand, the soluble part (25%) of the product obtained by WC&/R,$n catalysis has an IR spectrum resembling that of the ring-opened polymer of norbornene and is, therefore, thought to have structure 3 **I and to be formed by propagation through a metathesis-type mechanism, involving a metallacarbene carrier. *) Systematic name: poly(tricyclo(3.2.1 .03v7]o~t-4, I-ylenemethylene). **I Systematic name: poly(4-methylene-l,3-~yclopentylenevinylene).
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