New aspects of the mechanism of the ring-opening polymerization of cyclo-olefins

• Published in: Journal of molecular catalysis 1985, Vol.28 (1), p.337-349
• Main Authors: Ceausescu, E., Cornilescu, A., Nicolescu, E., Popescu, M., Coca, S., Belloiu, C., Dimonie, M., Gherorghui, M., Dragutan, V., Chipara, M.
• Format: Article
• Language: English
• ISSN: 0304-5102
• DOI: 10.1016/0304-5102(85)87039-5

The polymerization activity of the cyclopentene/WCl 6 system initiated by water has been correlated with the occurrence of paramagnetic species involving the lower oxidation states of tungsten as detected by ESR spectroscopy. The W(III) species formed by the cyclo-olefin-controlled reduction of WCl 6 were shown to be the precursors of the active species in polymerization reactions initiated by water in the absence of the alkylaluminium compound as a carbene source. The same W(III) species are assumed to be the precursor of the active species in the cyclopentene polymerization initiated by the WCl 6/i-Bu 3Al system. Attempts to polymerize cyclohexene in the presence of WCl 6/i-Bu 3Al failed; however, ESR signals assigned to W(V) and W(III) species were recorded. Independent studies carried out by mass spectrometry for the products resulting from the interaction between cyclopentene or cyclohexene and WCl 6 demonstrated the existence of well-defined cyclic hydrocarbons along with 3-chlorocyclopentene and 3-chlorocyclohexene, respectively. The formation of these compounds may be explained via a cationic mechanism. The mechanisms of the initiation and propagation steps in polymerizations generated by carbene species from cyclo-olefin and WCl 6 in the absence of alkylaluminium compounds are discussed. The role of the cyclo-olefin for reducing the tungsten compounds and producing the metallacarbene species is outlined. The sharp influence of strongly complexing additives on the reaction kinetics, catalyst activity and on the evolution of molecular weight with time in the polymerization of cyclopentene is presented.