Catalyse de transformation des oléfines par les complexes du tungstène, 4. Evolution de la distribution des masses moléculaires au cours de la polymérisation des cyclooléfines

The molecular weight distribution of polypentenamer and polyoctenamer prepared in the presence of tungsten catalysts, was studied by GPC, as a function of reaction time. Polypentenamer shows a single distribution, the maximum and width of which decrease with increasing conversion. Polyoctenamer prepared either from cyclooctene or from a polymer of high molecular weight, shows a bimodal distribution which may be considered as the sum of two single distributions. The relative proportions of these two distributions are independent of the conversion. Each distribution finally becomes “log-normal” at high conversion. The cyclopentene-cyclooctene copolymer also shows a bimodal distribution. The oligomers possess octenamer as well as pentenamer units. The simultaneous formation of polymers of high molecular weight and of oligomers is explained in terms of a polyaddition reaction at the bond between the metal and the carbeneresidue with intramolecular chain transfer.