The effect of the amido substituent on polymer molecular weight in propenehomopolymerisation by titanium cyclopentadienyl-amide catalysts

In the homopolymerisation of propene by the cyclopentadienyl-amide titanium catalyst systems [eta(5),eta(1)-C5H4(CH2)(2)NR]TiCl2/MAO and [eta(5),eta(1 )- C5H4(CH2)(2)NR]Ti(CH2Ph)(2)/B(C6F5)(3) (R = Bu-t, Pr-i, Me), the catalys t with the smallest substituent (Me) on the amido moiety consistently gives the highest polymer molecular weight. This differs from the trend usually observed in related catalysts with tetramethylcyclopentadienyl-amide ancill ary ligands, where larger amide substituents result in higher molecular wei ghts. Based on the present information a hypothesis is formulated in which an increased cation-anion interaction for the less sterically hindered cata lyst is responsible for disfavouring chain transfer relative to chain growt h.