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properties and the structural characteristics of polymers has been a target since the first appearance of polymer science [ 3 – 6 ]. Thermoplastic industries for polypropylene (PP) are mainly based on Ziegler–Natta catalyst technology. In 2000, the

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Ziegler-Natta catalytic systems

Calorimetric and DFT study on TiCl4-Lewis base interactions

Journal of Thermal Analysis and Calorimetry
Authors: L. Cavallo, J. Ducéré, Rosalisa Fedele, A. Melchior, Maria Mimmi, G. Morini, F. Piemontesi, and Marilena Tolazzi

Abstract  

A calorimetric investigation on the reactions of TiCl4 with phthalates in 1,1,2,2-tetrachloroethane (TCE) is presented in order to better understand the complex interactions present in Ziegler-Natta catalytic systems. The Lewis bases diethyl isophthalate (L1), diethyl terephthalate (L2) and the ortho-isomer diethylphthalate (L3), have been chosen to study how the substituent positions could influence the energy and the stoichiometry of the complexation reactions. FTIR spectroscopy was used to obtain information on the coordination mode of the ligands and diffusion measurements by NMR was carried out to verify the presence of oligo-or polymeric species. Experimental results were compared with theoretical calculations based on Density Functional Theory (DFT).

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Abstract  

The investigation of the intermolecular composition distribution of an ethylene/1-hexene copolymers using DSC method has been carried out. The known methods: step crystallization (SC) and successive self-nucleation/annealing (SSA) have been adapted for this purpose, and particularly, the optimal condition of the process have been chosen to enable the best fractional crystallization of the copolymer. The method has been applied for fractionation of two ethylene/1-hexenecopolymers synthesized with supported vanadium and zirconocene catalysts and having similar concentrations of 1-hexene. Although metallocene catalysts are known from their more homogeneous structure of active sites in comparison to multi-site Ziegler–Natta catalysts, the copolymers obtained over both catalytic systems gave DSC curves resolved into several peaks but with different melting points. Using the Thomson–Gibbs equation, comparable average lamellar thickness of the separated peaks has been calculated. The amounts of copolymer fraction with defined lamellar thickness have been determined. It was obtained that the copolymer produced from the metallocene system contains a thinner and more homogeneous lamella thickness than that obtained with Ziegler–Natta vanadium catalyst supported on the same carrier.

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China Petroleum Chemical Co. P.R. China. All the samples were produced on conventional Ziegler–Natta catalysts and the details of the molecular parameters of the samples are given in Table 1 . Table 1

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, Ferey , G , Visseaux , M 2009 Lanthanide metal-organic frameworks as ziegler-natta catalysts for the selective polymerization of isoprene . Macromol Chem Phys 210 : 1923 – 1932 10.1002/macp.200900354 . 13

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