Mechanistic aspects in propene polymerization using mgcl2-supported ziegler-natta catalysts: behaviour of silane as an external lewis base

Kinetic study of a highly active MgCl2‐supported Ziegler–Natta catalyst in liquid pool propylene polymerization. II. The influence of alkyl aluminum and alkoxysilane on catalyst activation and deactivation

“…This result shows that alkoxysilane as well as TEA is actually involved in the activation of the catalyst, as reported by Spitz and coworkers. 15,16 Figure 5 also shows that the response of ED addition is rather fast. This means that the coordination equilibrium of alkoxysilane is rapid between liquid propylene and the surface of the solid catalyst component even at low concentrations, as was suggested by Spitz et al 15 The mechanism of activation by alkoxysilane was explained by Spitz et al 15 Alkoxysilane as an ED converts a fluctuating site, which produces less isotactic PP, into a highly isotactic site.…”

“…15,16 Figure 5 also shows that the response of ED addition is rather fast. This means that the coordination equilibrium of alkoxysilane is rapid between liquid propylene and the surface of the solid catalyst component even at low concentrations, as was suggested by Spitz et al 15 The mechanism of activation by alkoxysilane was explained by Spitz et al 15 Alkoxysilane as an ED converts a fluctuating site, which produces less isotactic PP, into a highly isotactic site. 1,17 In general, the activity is higher at highly isotactic sites than at less isotactic sites because the propagation constant is higher at highly isotactic sites.…”

“…Interestingly, only the initial TEA concentration, that is, the TEA concentration when the solid catalyst component comes into contact with TEA for the first time, shows a clear tendency against R p,0 . The importance of the TEA concentration for catalyst activation was also pointed out by Spitz et al 15 Note that the initial TEA concentration without preactivation is low because TEA is dissolved in a large amount (2600 mL) of liquid propylene. However, the initial TEA concentration with preactivation is high because the amount of the solvent is very small (see the Experimental section).…”

Improvement in productivity and molecular weight of polypropene-block-poly(ethene-co-propene) obtained by a modified stopped-flow method using various external electron donors

“…However, one should consider the possibility of whether the external donor alone, the external donor/alkylaluminum complex, or a product of the decomposition reaction of the external donor with alkylaluminum is responsible for the poisoning. Trialkylaluminum compounds are recognized to react with silane compounds producing complexes [22][23][24][25] . Based on the consideration combined with our results in which the minimum Si/Ti mole ratio giving effective improvement of the molecular weight and the catalyst activity was 1.0, the influence of the pre-treatment of the catalyst with TEA in the presence of the external donor could be regarded as an interaction of the complex of TEA and the external donor with the active sites.…”

Polymerization of propylene by using MG(OEt)2-DNBP-TiCl4 catalyst with alkoxy disilanes as external donor

“…17 The structure of the 1/1 complex has been depicted by Iiskola et al 18 These authors have shown that the alkoxymonosilane as external donor was tightly connected to the active site structure, as a 1/1 complex with alkylaluminum.…”