Measuring on main kinetic parameters of molecular catalyst for olefin polymerization using high-pressure-type quenched flow reactor
Ziegler-Natta catalysts are generally obtained by the combination of a transition metal complex with an alkylaluminium compound and possibly another co-catalyst. For molecular Ziegler-Natta catalyst, generally, the active species is a cationic compound. However, in regards to the actives species, the olefin may compete in the polymerization medium with other metal alkyl, the solvent or the counteranion. Thus, it is not an easy task to determine the total active metal site fraction which remains an important challenge in the field of polyolefins. Several methods have been developed to perform this measurement. Among these the most reliable one is rely on the determination of number of macromolecules formed initially, and it requires working in initial controlled regime where the chain transfer reactions are very limited. It should be possible to achieve the controlled regime for molecular catalyst for time going from several milliseconds to fraction of second. This means that technically demanding fast kinetic techniques such as quenched flow technique are necessary for the investigation of kinetic parameters of olefin polymerization catalysts. Up to now this technique has been only implemented in very mild conditions. Recently a stopped flow reactor operating at high temperature and high pressure has been developed in Lyon. In the present study, the usefulness of this reactor for measuring the chain propagation rate constant kp and the fraction of metal active site [M*]/[M] is assessed. In the first part of this work we have focused on the investigation of some metallocene-based catalysts. In particular, we have observed how these catalysts behave at initial stage of polymerization, when they are activated with different co-catalyst and in some case a kinetic description was also possible. The last part of this work was dedicated to kinetic study of some post-metallocene catalysts such as amine bisphenolate and (bis phenoxy-imine) -Zr and -Ti based complexes activated with MAO in a large range of polymerization temperatures. A successful kinetic investigation of Bis(cumyl)[ONNO]ZrBz2 complex activated with MAO/tBu2-PhOH has been performed which allowed the determination of [M*]/[M], kp and activation parameters such as H‡ and S‡. In the case of [N-(3-tert-butylsalicylidene)-2,3,4,5,6 pentafluoroanilinato] titanium dichloride activated with MAO an original changing in kinetic regime is reported by increasing the polymerization temperature