Propene/Ethene-[1-¹³C] Copolymerization as a Tool for Investigating Catalyst Regioselectivity. MgCl₂/Internal Donor/TiCl₄−External Donor/AlR₃Systems

Abstract

The propene/ethene-[1-13C] copolymerization method has been applied to measure precisely the regioselectivity of two modern MgCl2-supported Ziegler−Natta catalyst systems for the industrial production of isotactic polypropylene, namely MgCl2/di(isobutyl)-o-phthalate/TiCl4−cyclohexylmethyldimethoxysilane/AlR3 (1) and MgCl2/2,2-di(isobutyl)-1,3-dimethoxypropane/TiCl4−AlR3 (2). System 2 turned out to be slightly less regioselective than system 1 (on average, 0.26% 2,1 misinsertions instead of 0.18%), but the distribution of the regiodefects throughout the polymer was found to be more uniform, most likely as a result of a lower differentiation of the active species. This provides a simple explanation for the different response of the two catalysts to molecular hydrogen as a chain transfer agent. In system 1, indeed, part of the active species are almost completely regioselective, which means that H2 finds very few preferential “cutting points” in the form of growing chains with a sterically hindered 2,1 last-inserted unit; therefore, a higher H2 partial pressure is neededcompared with system 2in order to achieve the same decrease of average polymer molecular mass.

Spectroscopic Investigation of Heterogeneous Ziegler–Natta Catalysts: Ti and Mg Chloride Tetrahydrofuranates, Their Interaction Compound, and the Role of the Activator

“…More recently, also the role of electron-donor molecules has been revisited. [13,22] In the new models, the donor molecules are supposed to have a direct role in the shape definition of the active pocket around the Ti center, which in turn suggests that these molecules interact directly with the catalytic Ti sites, and are able to exert non-bonded interactions with the growing polymer chain and/or the incoming monomer. The current scenario is extremely complex, and it is clear that all the catalyst components strongly interact with one another.…”

Hydrogen Effects for Propylene Polymerization with Ultra Low TiCl3 Loading MgCl2‐Supported Catalyst

“…In order to overcome this problem, more detailed understanding of the hydrogen acting mechanism has been regarded as the most important subject. [5,6] In a series of our studies, the hydrogen effects were investigated with the stoppedflow technique, by which the chain transfer reactions by Al-alkyl cocatalyst or monomer could be negligible and quasi-living polymerization can be realized within an extremely short polymerization period (ca. 0.2 s).…”

“Dormant” secondary metal-alkyl complexes are not omnipresent

“…This series of study, initially performed for two siliconbridged indenyl systems (2), has been extended to include the predecessor of heterogeneous catalysts (1) and two modern systems with a Lewis base (3). The plentitude and miscellany of systems displaying dormancy, discussed in refs.…”