Comparative study of propylene polymerization using Me2Si(RInd)2ZrCl2/SiO2-SMAO/AlR3 and Me2Si(RInd)2ZrCl2/MAO (R = Me, H)

A mechanistic analysis of propylene polymerization was performed, in which the catalyst system was Me₂Si(R¹Ind)₂ZrCl₂/SMAO/AlR₃² (in situ supported catalyst onto MAO-modified silica) or Me₂Si(R¹Ind)₂ZrCl₂/MAO (homogeneous), where R¹ = H or CH₃, cocatalyzed by AlR₃² = TEA (triethylaluminum), IPRA (isoprenylaluminum), or TIBA (triisobutylaluminum). The catalyst activity of the homogeneous system Me₂Si(2-Me-Ind)₂ZrCl₂/MAO was almost 8 times higher than that observed for Me₂Si(Ind)₂ZrCl₂/MAO (38 vs 4.6 kg PP/g cat h), while the polypropylene molar mass was 3 times higher (M_w: 93 vs 34 kg/mol). Conversely, the in situ supported systems Me₂Si(Ind)₂ZrCl₂/SMAO/AlR₃ and Me₂Si(2-Me-Ind)₂ZrCl₂/SMAO/AlR₃ showed similar activities, ranging from 0.2 to 1.5 kg PP/g cat h. The molar mass of the resulting polymers prepared using the in situ procedure was dependent on the AlR₃ nature and on the Al/Zr ratio. Generally, the heterogeneous catalysts produced PP with higher molecular weights than that obtained with homogeneous ones. The influence of the alkylaluminum, used as the cocatalyst, on the chain-transfer termination reaction to the alkyl compound was evident from the activity and the molecular weight of the produced polymers.