Determination and tracing of active and dormant propagation chains in 1-hexene polymerization with supported Ziegler―Natta catalyst

Abstract Propagation chains with 1,2 and 2,1 last-inserted monomer unit in 1-hexene polymerization with MgCl2-supported Ziegler-Natta catalysts were quench-labeled by thiophene-2-carbonyl chloride, and the two kinds of 2-thenoyl-labeled chain ends were determined by 1H NMR analysis. The number of labeled chains was noticeably smaller than the number of dead chains formed by chain transfer with alkylaluminum cocatalyst, and grew with time more slowly than the latter, showing that side reactions between the quencher and Al-polymeryl moieties are negligible. The active sites with 2,1 last-inserted monomer were halted in dormant state, which lead to their gradual accumulation in the 30 s polymerization process. The catalyst containing phthalate type internal donor has higher percentage of dormant sites as compared with the catalyst containing diol ester. The combination of acyl chloride quench-labeling and 1H NMR analysis forms a reliable and easily accessible method of tracing and characterizing active sites in transition metal catalyzed olefin polymerization.