| abstract |
In a polymerization of alpha mono-olefins by means of certain supported coordination catalysts systems which comprise (a) a procatalyst, (b) a cocatalyst, and (c) a selectivity control agent, wherein (a) is a highly active solid composition which comprises magnesium chloride, titanium tetrachloride and an electron donor; and (b) is an aluminum trialkyl; the selectivity control agent comprises a strong selectivity control agent and a weak selectivity control agent. |