Effect of AlEt₃and an External Donor on the Distribution of Active Sites According to Their Stereospecificity in Propylene Polymerization over TiCl₄/MgCl₂Catalysts with Different Titanium Content

Abstract

The data on content of individual fractions with different microtacticity for poly(propylene) (PP) samples produced over titanium–magnesium catalysts (TMCs) with composition TiCl4/MgCl2 and different titanium contents (0.1 and 3.5 wt%), as well as on the effects of pretreatment of these catalysts with triethylaluminum and addition of an external electron donor to the polymerization reaction on the content of these fractions are obtained using preparative temperature rising elution fractionation. The TMC with low titanium content is found to contain more than 90% of aspecific sites and an insignificant number of sites with low isospecificity (IS1) and isospecific sites (IS2). Pretreatment of catalysts with triethylaluminum increases the contents of the IS1 and IS2 sites. Addition of an external donor results in a more noticeable increase in the contents of IS1 and IS2 sites and formation of highly isospecific IS3 sites. The data on molecular weight and thermophysical properties of individual PP fractions with different microtacticity produced over catalysts with different compositions are obtained.

Effects of titanium dispersion state on distribution and reactivity of active centers in propylene polymerization with MgCl2‐supported Ziegler‐Natta catalysts: A kinetic study based on active center counting

“…Cat-1 with ultralow Ti content is used as a model catalyst that mainly contains isolated mononuclear Ti species. [18][19][20][21][22][23][24][26][27][28][29][30] Cat-2 with higher Ti content and more clustered Ti species is similar with those supported ZÀ N catalysts used in polyolefin industry. Therefore, the catalysts used here can be taken as models for the two extremes of Ti dispersion states.…”

“…Similar phenomena have been reported in previous literatures. [34][35][36] It can be found that the melting temperature (T m ) and melting enthalpy (ΔH m ) gradually increased with proceeding of the polymerization for both catalysts. However, the T m and ΔH m of PP catalyzed by Cat-1 were lower than those of PP catalyzed by Cat-2 under the same conditions.…”

“…Similar phenomena have been reported in literatures dealing with similar model catalysts of different Ti load. [18][19][20][21][22][23][24][26][27][28][29][30] Due to broad distribution of stereoregularity, two endothermic peaks were observed on DSC heating trace of each PP product (see Figure S1 of Supporting Information). The glass-transition temperature appeared at around À 9°C (see Figure S1).…”

Propylene polymerization over supported Ziegler–Natta catalysts: Effect of internal and external donors on distribution of active sites according to stereospecificity

“…Stereospecificity of active sites depends on the additional surface compounds (aluminum alkyls or electron‐donating compounds) adsorbed on the neighboring metal ions in the second coordination sphere of active Ti ions. We have recently used this model for discussion of our results regarding the effect of organoaluminum cocatalyst and ED on the formation and distribution of fractions with different microtacticities for PP produced over the “donor‐free” TMC with very low titanium content at polymerization in the absence and presence of the ED …”

“…We have recently used the p‐TREF technique to study the distribution of active centers according to stereospecificity in “donor‐free” TiCl 4 /MgCl 2 catalysts with different titanium contents . In case of the catalyst with a very low titanium content (0.1 wt % of Ti), a much higher amount of non‐stereoregular (“atactic”) fraction (65%) is formed compared to the regular supported catalyst containing (3.5 wt % of Ti 35% of the “atactic” fraction).…”