Specific behaviour of cycloolefins in ring-opening polymerisation

• Published in: Journal of molecular catalysis 1988-07, Vol.46 (1), p.433-444
• Main Authors: Ceausescu, E., Cornilescu, A., Nicolescu, E., Popescu, M., Coca, S., Cuzmici, M., Oprescu, C., Dimonie, M., Hubca, G.H., Teodorescu, M., Dragutan, V.
• Format: Article
• Language: English
• ISSN: 0304-5102
• DOI: 10.1016/0304-5102(88)85115-0

The relationship between the behaviour of cycloolefins in ring-opening polymerisation and copolymerisation and the ring size of the cycloolefin and nature of the catalytic system has been thoroughly studied [1], relating especially to the monomer reactivity, kinetic parameters, reaction stereochemistry and polymer structure. The results obtained in the reactions of cyclopentene, cyclohexene, cyclooctene, 1,5-cyclooctadiene and cyclododecene in the presence of WCl 6-based catalysts indicate that the monomer strongly influences the polymerisation process owing to its electronic, steric and thermodynamic characteristics. The oxidation state of the tungsten atom was found to be a determinant factor in exhibiting the particular behaviour of these cycloolefins. It was observed that cyclopentene reduces WCl 6 to the paramagnetic W(V) and W(III) species, while cyclohexene, cyclooctene and cyclododecene reduce WCl 6 to W(V), at specific rates, determined by the cycloolefin. For catalysts derived from WCl 6 and organotin or organosilicon compounds, a high oxidation state of the tungsten atom, W(V) or W(VI), is characteristic. These catalytic systems polymerise cyclopentene at high rates, to give cis-poly-pentenamer at −30 °C, but are totally inactive towards cyclooctene and cyclododecene at room temperature or at −30°C. It is significant that the polymerisation of the last two cycloolefins takes place if the above catalytic systems were pre-contacted with small amounts of cyclopentene, cyclohexene or 1,5-cyclooctadiene. In addition, 1,5-cyclooctadiene exhibited a high reactivity toward the above catalysts at room temperature. In the presence of ternary catalytic systems (WCl 6-Bu 3Al-epichlorohydrin and WCl 6-i-Bu 3Al-chloranil), where a low valence state of the tungsten atom is encountered (2.8–3.2), cyclopentene leads specifically to trans polypentenamer. Furthermore, these catalysts readily induce the ringopening polymerisation of cyclooctene, 1,5-cyclooctadiene and cyclododecene. The reactivity of the above monomers was found to be similar in both polymerisation and copolymerisation reactions and varied as follows: cyclopentene > 1,5-cyclooctadiene > cyclododecene > cyclooctene. The specific behaviour of the above cycloolefins in the presence of WCl 6-based catalytic systems is discussed in terms of the metallacarbenemetallacyclobutane mechanisms, supposing that several types of active centres are possible.