Counting the number of active centers in MgCl2-supported Ziegler–Natta catalysts by quenching with 2-thiophenecarbonyl chloride and study on the initial kinetics of propylene polymerization

Using 2-thiophenecarbonyl chloride (TPCC) as a quenching agent, the number of active centers in propylene polymerization with MgCl2-supported Ziegler–Natta catalysts were determined by measuring the sulfur content of the quenched polymer. Under suitable conditions, the thiophenecarbonyl-labeled polymer chains were stable in the reaction system when TPCC/Al > 1. The number of active centers was found to increase in the first 5 minutes of propylene polymerization, accompanied by rapid decrease of the propagation rate constant kp. Diffusion barrier from the polymer covering the catalyst fragments is thought as the main reason of the rapid decay of kp in the initial stage.

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► 2-Thiophenecarbonyl chloride was used as quenching agent.
► Number of active center in MgCl2-supported Z-N catalyst is counted with high accuracy.
► Initial kinetics of propylene polymerization was studied with the method.
► Gradual initiation of the active centers is accompanied by rapid decrease of kp.
► Diffusion barrier from polymer covering the catalyst accounts for decrease of kp.