The distributions of molecular weight and chemical composition of two linear low‐density polyethylene resins synthesized with Ziegler‐Natta catalysts were analyzed with several microstructural characterization techniques and the results were used to investigate the nature of the active site types present on the catalyst. Deconvolution of the molecular weight distribution measured by gel permeation chromatography and of the chemical composition distribution measured by either crystallization analysis fractionation or temperature rising elution fractionation leads to consistent results that indicate the presence of multiple active site types on the catalyst. This shows that these fractionation techniques, when combined with adequate mathematical models, are powerful tools to understand the behavior of Ziegler‐Natta catalysts and structural properties of the produced resins.

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A series of Ziegler-Natta catalysts, with and without diisobutylphtalate as an internal donor, were modified with alkylaluminum (triethylaluminum or diethylaluminum chloride) and an external donor (diisopropyldimethoxysilane or methyltrimethoxysilane), in increasing complexity. The resulting catalysts were characterized by X-ray photoelectron spectroscopy and extended X-ray absorption fine structure analysis (EXAFS) and evaluated in propylene polymerization. According to EXAFS oscillation, systems bearing diisobutylphtalate as an internal donor displayed a well-defined pattern, suggesting a more ordered structure around the Ti atom. EXAFS data treat-ment provided two TiÀ ÀCl distances: $ 1.96 and 2.5 Å . The former was shown to have a linear dependence on the Ti (2p 3/2 ) binding energy as the catalyst is modified with TEA or with external donors. Conversely, the longest distance is reduced as Ti (2p 3/2 ) binding energy increases with catalyst modification. Correlations involving the catalyst activity, Ti (2p 3/2 ) binding energy, and TiÀ ÀCl distances could be denoted.