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

Abstract

A mechanistic analysis of propylene polymerization was performed, in which the catalyst system was Me2Si(R1Ind)2ZrCl2/SMAO/AlR 3 2 (in situ supported catalyst onto MAO-modified silica) or Me2Si(R1Ind)2ZrCl2/MAO (homogeneous), where R1 = H or CH3, cocatalyzed by AlR3 2 = 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 (Mw: 93 vs 34 kg/mol). Conversely, the in situ supported systems Me2Si(Ind)2ZrCl2/SMAO/AlR3 and Me2Si(2-Me-Ind)2ZrCl2/SMAO/AlR 3 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.