With the bimetallic supported catalyst at disposal, it is crucialto fully activate the two catalytically active metals before molec-ular weight-disparate PP chains can be simultaneously generatedto afford broad/bimodal MWD PP. However, it has been reportedthat triethylaluminum (TEA), the most frequently used cocatalystfor Ziegler–Natta catalyst, is prone to complex with MAO-activatedmetallocene catalyst forming bimetallic stable species that deac-tivates the metallocene during propylene polymerization [24];nonetheless, triisobutylaluminum (TIBA), with bulky alkyls, canbe exempted from that negative effect and even boost the poly-merization by possibly functioning as a scavenger Consideringthat the bimetallic “two-in-one” catalyst contains much less Zr(0.56 wt%) than Ti (1.74 wt%) and at a normal molar ratio of tri-alkylaluminum to Ti (Al/Ti) to ensure a best performance of theZiegler–Natta catalyst (usually around 100) the amount of tri-alkylaluminum relative to the metallocene will be massive, wefirst tested the effects of TEA and TIBA on neat rac-[CH2(3-t-Bu-1-Ind)2]ZrCl2/MAO-catalyzed propylene polymerization to clarifytheir roles in the metallocene-functioned polymerization. Theseresults are summarized in Table 1. In this case the molar ratioof MAO to Zr was set at 1500, which should be appropriate for ametallocene-catalyzed solution polymerization. The ratios of TEAand TIBA to Zr were deliberately varied in a relatively high rangeof 500–4000. As evidenced, rac-CH2(3-t-Bu-1-Ind)2ZrCl2activatedby MAO is able to produce PP with a high activity, although themolecular weights and melting temperatures of polymers are bothmoderate due to solution polymerization conditions. However,when excess TEA were present in the polymerization, the cata-lyst activities gradually reduced at a relatively fast pace. On thecontrary, even at such high concentrations, TIBA did not causeany loss of catalyst activity, nor did it reduce the polymer molec-ular weights. With even higher catalyst activities, TIBA-presentpolymerizations produced PP no different from neat rac-CH2(3-t-Bu-1-Ind)2ZrCl2/MAO-produced ones.