Influence of Ziegler−Natta Catalyst Regioselectivity on Polypropylene Molecular Weight Distribution and Rheological and Crystallization Behavior

Abstract

Fundamental implications of occasional secondary (2,1-) insertions in propene polymerization with different MgCl2-supported Ziegler-Natta catalysts are discussed, with reference to the properties of the polymers obtained. The relatively narrow molecular weight distribution of polypropylene prepared using catalysts of type MgCl 2/TiCl4/diether-AlR3 is ascribed to the fact that the active species in this system are relatively uniform, in the sense that significant 2,1-insertion takes place at both highly isospecific and weakly isospecific active species. In contrast, the isospecific species in the catalyst system MgCl 2/TiCl4/diisobutyl phthalate-AlEt3-alkoxysilane undergo less 2,1-insertion and are therefore less responsive to chain transfer with hydrogen. The presence of (some) highly regiospecific active sites in such catalysts will therefore lead to the formation of a high molecular weight polymer fraction and, overall, a broad molecular weight distribution. The presence of high molecular weight chains leads to relatively slow molecular relaxation and a more rapid onset of crystallization of the polymer from the melt, as evidenced by rheological studies of polypropylenes prepared using different catalysts and having different molecular weight distributions.

Influence of Internal Donors on the Performance and Structure of MgCl2 Supported Titanium Catalysts for Propylene Polymerization

“…[5][6][7][8][9] The main focus in the production of polypropylene is the continual development and improvement of existing catalysts, to achieve higher productivity with stereospecific control for the desired physico-chemical properties of the product. The wider applications of polypropylene in vast end uses is due to good mechanical properties, chemical resistance, and excellent insulation characteristics.…”

Nature of Phthalates as Internal Donors in High Performance MgCl2 Supported Titanium Catalysts

“…TiCl 4 reacts with DIBP (5) to form product 7, which in the presence of excess amount of TiCl 4 gives phthaloyl chloride (8). Product 7 on reacting with 4 results in isobutyl ethyl phthalate (9) formation and phthaloyl chloride on reacting with 4 results in the formation of diethylphthalate (10). Internal donors (ID), Scheme 1, (5), (7), (8), (9) and (10) (Lewis bases) and TiCl 4 get coordinated to MgCl 2 matrix, forming the active catalyst.…”

“…High performance MgCl 2 supported Ziegler-Natta catalysts have played dominant role in industrial polyolefin production [1][2][3][4][5] by providing high productivity and stereoregularity [6][7][8][9][10][11]. Internal donors play the pivotal role in controlling productivity and stereo-specificity of these catalysts [12][13][14][15][16][17][18].…”

Propylene Polymerization over MgCl2‐Supported Ziegler–Natta Catalysts Containing Tri‐Ether as the Internal Donor

“…26 Concerning the high activity and high hydrogen response of the diether-based catalysts, it was reported that dietherbased catalysts had a high content of active sites with low regioselectivity, 19 that this effect can be ascribed to chain transfer after the occasional secondary (2,1-) rather than the usual primary (1,2-) insertion. 27 Additionally, the 1,3-diether strongly coordinates to the support and cannot be easily extracted 2 from the catalyst surface on contact with a cocatalyst such as alkylaluminum 19 because the 1,3-diether show higher affinity toward magnesium chloride than to a cocatalyst, and consequently diether-based catalysts make polypropylene having comparatively high isotacticity without an external donor. 16,19 The development of new electron donors (Lewis bases, usually containing oxygen atoms) is one of the chief areas of research in Ziegler-Natta olefin polymerization systems.…”