Solution-state NMR study of organic components of industrial Ziegler-Natta catalysts: Effect of by-products on catalyst performance

Abstract

Chemical routes for preparing Ziegler-Natta (ZN) catalysts accompany the formation of by-products that remain in final catalysts in different amounts. In the history of ZN catalysts, much less emphasis has been given to analyze such by-products present in catalysts. Herein, we prepared various Mg(OEt)2-based ZN catalysts and conducted solution-state NMR measurements to characterize and quantify the organic components of these catalysts. It was found that, depending on the molecular structure of the internal donor (ID) and catalyst preparation conditions, an ID can undergo side reactions to produce organic by-products. All the catalysts contained different amounts of titanium alkoxy by-products formed in the reaction between Mg(OEt)2 and TiCl4, which were detrimental for the catalyst activity. These by-products were responsible for increasing the amount of the amorphous fraction in polypropylene and decreasing the highly crystalline fraction's stereoregularity. Possible hypotheses to explain the negative impacts of titanium alkoxy by-products are discussed.