Authors:Hanieh Nassiri, Hassan Arabi, and Shokoufeh Hakim
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–Nattacatalyst technology. In 2000, the
Authors:L. Cavallo, J. Ducéré, Rosalisa Fedele, A. Melchior, Maria Mimmi, G. Morini, F. Piemontesi, and Marilena Tolazzi
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
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).
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.