Selective Quench-Labeling of the Hafnium-Pyridyl Amido-Catalyzed Polymerization of 1-Octene in the Presence of Trialkyl-Aluminum Chain-Transfer Reagents

Abstract

The pyrenyl-isonitrile quench-labeling reagent selectively labels Hf-polymeryls over Al-alkyl species allowing for quantification of active site counts in polymerization. This selectivity also enables differentiation between catalyst-bound and Al-bound polymer molecular weight distributions (MWDs) via dual detection gel permeation chromatography (GPC) methods (UV-GPC and RI-GPC) in the Hf-pyridyl amido-catalyzed polymerization of 1-octene. Inhibition of polymerization is observed when using trialkyl aluminum chain-transfer agents with this catalyst system; for AlEt3, such inhibition can be eliminated by addition of the chain-transfer reagent after initiation of polymerization. Inhibition of polymerization cannot be eliminated when AlMe3 is used in these polymerizations. With AliBu3, a larger s-branched Al-alkyl, polymerization is not inhibited. For AlEt3, the propagation to exchange coefficient (kex/kp) was determined; compared with ZnEt2, chain transfer is approximately an order of magnitude slower. Thro...