Characterization of MgCI2-supported catalyst and initial kinetics determination in low-pressure propene polymerization

The scope of the presented research was focused on the 4th generation of MgCl2- -supported TiCl4 catalyst behavior at low temperature (30 – 40°C) a nd pressure (1 atm) during propene polymerization in n-heptane slurry. The influence of triethylaluminium (TEA) cocatalyst, prepolymerization and propene concentration on the catalyst and polymer properties was investigated. Special attention was devoted to the determination of the initial polymerization kinetics. For this purpose, a new technique for the determination of initial kinetic profile in the first seconds of polymerization was developed. It is based on the accurate timing of short polymerizations resulting from the immediate start of a reaction between the catalyst separated in oil phase and the remaining components of the system upon their being mixed together. Consequent complementation with the kinetic measurements based on monomer consumption allowed the exact determination of the catalyst behavior since the first seconds of polymerization up to one hour. Furthermore the comparison of the catalyst behavior during the initial polymerization stage in the different environments of gas-phase and n-heptane slurry was investigated. The initial kinetic profile in the gas-phase was determined using the special fixed-bed reactor, allowing the fast change of the gas composition and precise control of the polymerization time. Moreover, the polymer samples obtained from the short-time experiments were utilized for the determination of their molecular weight distribution by GPC/SEC analysis. Then the number of active sites and propagation rate coefficients could be evaluated from the dependence of the number of macromolecules on polymer yield. Furthermore the microstructure of the selected samples was analyzed by 13C-NMR measurement. On the basis of the presented results, a theory based on the TEA monomer-dimer equilibrium was postulated for the interpretation of the observed kinetic profiles at low TEA concentrations. Furthermore the GPC/SEC and 13C-NMR analyses revealed that the TEA influences directly the nature of the active site, probably by forming bimetallic complexes. In the last Chapter, the difference between the polymerizations carried out in gasphase and n-heptane slurry at low temperature and pressure is discussed. The obtained data indicate the significant influence of the monomer concentration in the polymer layer surrounding the catalyst particles.