Accurately measuring mol. kinetics of catalytic olefin polymn. has been a challenging objective. Many methods have been proposed in the literature, but all of them have drawback(s). In this paper, we introduce a labeling method to count active sites employing Me propargyl ether (MPE) as the quench-labeling agent. It is com. available, does not react with Al-alkyl species, and has a labeling efficiency close to 100%. The labeling reaction was evidenced by a mechanistic study on the reaction between the model system Cp2ZrMe2/MAO (Cp = cyclopentadienyl) and MPE that it may occur through a coordination-insertion mechanism without noticeable multiple insertions. The method was benchmarked by studying a MgCl2-supported Ziegler-Natta catalyst in 1-hexene polymn. The fraction of the active transition metal χ* is found to be <1%. It rises in the very first few seconds and reaches a plateau within 10 s in the absence of precontact. With precontact, χ* remains const. over polymer yield from 0.3 up to 5.3 g(PH) g(cat)-1, demonstrating that χ* does not necessarily grow during polymn. Longer precontact resulted in decreased χ* and decreased av. rate const. of propagation which is in the order of 102 M-1 s-1.
Alkynyl Ether Labeling: A Selective and Efficient Approach to Count Active Sites of Olefin Polymerization Catalysts / Yu, Yue; Cipullo, Roberta; Boisson, Christophe. - In: ACS CATALYSIS. - ISSN 2155-5435. - 9:4(2019), pp. 3098-3103. [10.1021/acscatal.8b04624]
Alkynyl Ether Labeling: A Selective and Efficient Approach to Count Active Sites of Olefin Polymerization Catalysts
Cipullo, Roberta;
2019
Abstract
Accurately measuring mol. kinetics of catalytic olefin polymn. has been a challenging objective. Many methods have been proposed in the literature, but all of them have drawback(s). In this paper, we introduce a labeling method to count active sites employing Me propargyl ether (MPE) as the quench-labeling agent. It is com. available, does not react with Al-alkyl species, and has a labeling efficiency close to 100%. The labeling reaction was evidenced by a mechanistic study on the reaction between the model system Cp2ZrMe2/MAO (Cp = cyclopentadienyl) and MPE that it may occur through a coordination-insertion mechanism without noticeable multiple insertions. The method was benchmarked by studying a MgCl2-supported Ziegler-Natta catalyst in 1-hexene polymn. The fraction of the active transition metal χ* is found to be <1%. It rises in the very first few seconds and reaches a plateau within 10 s in the absence of precontact. With precontact, χ* remains const. over polymer yield from 0.3 up to 5.3 g(PH) g(cat)-1, demonstrating that χ* does not necessarily grow during polymn. Longer precontact resulted in decreased χ* and decreased av. rate const. of propagation which is in the order of 102 M-1 s-1.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
