INITIATION OF POLYMERIZATION OF PHENYLACETYLENE WITH WOCl4 AND WCl6 "SINGLE-COMPONENT" METATHESIS CATALYSTS
Jiøí Vohlídal1, Jan Sedláèek1, Marta Pacovská1, Majda Žigon2
1Department of Physical and Macromolecular Chemistry,
Laboratory of Specialty Polymers*, Faculty of Science, Charles University,
Albertov 2030, CZ-128 40 Praha 2, Czech Republic, E-mail: email@example.com
2Polymer Department, National Institute of Chemistry, Hajdrihova 19, SLO-61115 Ljubljana, Slovenia
At low monomer-to-catalyst mole ratio (3:1) in benzene or toluene, phenylacetylene (PhA) re-acts with WOCl4 to arylderivatives belonging to five homologous series with increment equal to PhA unit, low amount of chloroderivatives and traces of PhA oligomers, mainly cyclotrimers. Aryls built in the derivatives originate from the solvent used. Hydrogen transfers between PhA units were found to participate in the overall reaction. An increase in the PhA/WOCl4 mole ratio results in a lowered yield of arylderivatives, higher yield of cyclotrimers and formation of higher PhA oligomers (ratio 12:1) or poly(phenylacetylene) (ratio 100:1). Chloroderivatives are formed in comparable amounts at any PhA/WOCl4 mole ratio so that they can be regarded as the key by-product of reduction of WOCl4 to low-valent tungsten species. In reaction systems with the mole ratio up to 12:1, WOCl4 is transformed into black solid assigned to WOCl2. It dissolves in PhA inducing its polymerization in which only PhA cyclotrimers are the side products. Formation of aryl- and chloroderivatives as well as tungsten growing species is discussed in terms of reaction pathway presuming an important role of oxo ligand of tungsten species. Reaction of PhA with WCl6 results in a formation of various PhA chloroderivatives and a fine precipitate of reduced tungsten species, which polymerizes PhA after poorly reproducible induction period.