In-Reactor Polypropylene FunctionalizationThe Influence of Catalyst Structures and Reaction Conditions on the Catalytic Performance

To unravel the relationship between silylene-bridged metallocene catalyst structures and polymerization conditions and their effect on the performance in in-reactor functionalization of polypropylene, the behaviors of rac -Me 2 Si­(2-Me-4-Ph-Ind) 2 ZrCl 2 /MMAO, rac -Me 2 Si­(Ind) 2 ZrCl 2 , rac -Me 2 Si­(2-Me-4-Ph-Ind) 2 HfCl 2 , and rac -Me 2 Si­(Ind) 2 HfCl 2 in propylene/aluminum alkyl-passivated 10-undecen-1-ol copolymerization were compared. Kinetic analysis revealed higher catalytic activities for zirconocenes compared to analogous hafnocenes. Both the zirconocene and hafnocene with substituted indenyl ligands afforded a higher molecular weight capability, improved stereo-selectivity, and enhanced ability to incorporate functionalized comonomers compared to their non-substituted congeners. An in-depth study of polypropylene functionalization using the best performing catalyst system, rac -Me 2 Si­(2-Me-4-Ph-Ind) 2 ZrCl 2 /MMAO, at temperatures ranging from 40 to 100 °C, revealed a linear inversely proportional correlation of polymerization temperature with functionalized comonomer reactivity (↑ T p → ↓ r 1 ), copolymer molecular weight (↑ T p → ↓ M n ), and melting temperature (↑ T p → ↓ T m ). While performing well under standard laboratory polymerization conditions, rac -Me 2 Si­(2-Me-4-Ph-Ind) 2 ZrCl 2 /MMAO showed limited molecular weight and stereo-selectivity capabilities under high-temperature (130–150 °C) solution process conditions. Although immobilization of rac -Me 2 Si­(2-Me-4-Ph-Ind) 2 ZrCl 2 onto silica, allowing it to be used under industrially relevant slurry and gas-phase conditions, led to an active catalyst, it failed to incorporate any functionalized comonomer.