Preparation and properties of polyallenes. Part I Polymerization of allene by Ziegler-type catalysts

The polymerization of allene induced by organoaluminum-vanadium oxytrichloride catalysts has been investigated in aliphatic hydrocarbons and at normal pressure. For the catalysts investigated, the polymerization activity decreases at decreasing order of alkylation of the aluminum alkyl: AIR3 > AIR2X > AIRX2 (R is Et or i-Bu; X is halogen). Compared with other aluminum trialkyls, trimethylaluminum shows a low activity. For the Al-i-Bu3-VOCl3 system, the effects of catalyst ratio, reaction time, and temperature have been studied. The polyallenes obtained are generally highly crystalline and melt between 115 and 125½C. The structure of the polymers was investigated by means of an NMR-infrared analysis. The activity of the initiating systems has been related to reactions taking place between the catalyst components. It is concluded that active catalysts are formed under conditions that favor the formation of vanadium (I1 or 111)-aluminum complexes of a relatively low solubility and stability. A polymerization mechanism is proposed in which the propagation starts with a coordination of the monomer with a vanadium center. In the next step the monomer is inserted into the vanadium-carbon bond of the growing polymer chain. It is assumed that the chain grows at the central carbon atom of the monomer unit. Vinyl and internal double bonds may have been formed as a result of isomerization of the chain end by a proton shift. © 1968, Taylor & Francis Group, LLC. All rights reserved