Description:
<jats:title>Abstract</jats:title><jats:p>The results of <jats:sup>13</jats:sup>C NMR analysis of chain end groups of poly(propylene) samples prepared with traditional δ‐TiCl<jats:sub>3</jats:sub> and high yield TiCl<jats:sub>4</jats:sub>/MgCl<jats:sub>2</jats:sub> catalysts in the presence of different <jats:sup>13</jats:sup>C enriched alkylaluminium cocatalysts — Al(<jats:sup>13</jats:sup>CH<jats:sub>2</jats:sub>CH<jats:sub>3</jats:sub>)<jats:sub>3</jats:sub>, Al(<jats:sup>13</jats:sup>CH<jats:sub>2</jats:sub>CH<jats:sub>3</jats:sub>) (is‐o‐C<jats:sub>4</jats:sub>H<jats:sub>9</jats:sub>)<jats:sub>2</jats:sub> and Al(<jats:sup>13</jats:sup>CH<jats:sub>2</jats:sub>CH<jats:sub>3</jats:sub>)(CH<jats:sub>3</jats:sub>)<jats:sub>2</jats:sub> — have been compared. The data show that, while molecular weights and fraction distribution change from one cocatalyst to another, the mechanism of steric control is the same independent of the cocatalyst used. This supports the hypothesis that the role of the metal alkyls is that of activating the solid catalyst by alkylation of the titanium surface complexes, but they do not participate directly in the structure of the active center.</jats:p>