Nonisothermal, uncontrolled homo- and copolymerization of ethylene using selected zirconocenes

Nonisothermal, uncontrolled polymerization, conducted in varying mixing regimes, offered a facile methodology to evaluate the influence of several important process development factors such as mixing, reaction exotherm, and thermal perturbations on the catalytic activity and kinetic stability, polymerization performance, and properties of the resulting polymers. Ethylene was homo- and copolymerixed with hexene-1 under varying impeller speeds (hence, thermal perturbations), using Ind₂ZrCl₂ and Et(Ind)₂ZrCl₂ and the MAO cocatalyst. With respect to the effects of the above process development actors, the following was observed: The reaction exotherm profiles, tracing the polymerization history, qualitatively represented the kinetic profile and the catalytic stability. The unbridged Ind₂ZrCl₂ was shown to be more stable than the bridged Et(Ind)₂ZrCl₂. With change in the level of stirring from a diffusion-controlled regime to a noodiffusion-controlled, external gas-liquid mass-transfer resistance-free one, the reaction exotherm and the run time-average catalytic activity increased. So far as the influence of the chiral versus the achiral zironocene structure is concerned, the copolymer composition distribution and soluble fraction generated by chiral Et(Ind)₂ZiCl₂ were more sensitive to the mixing conditions and thermal perturbations than were those produced by achiral Ind₂ZrCl₂. Et(Ind)₂ZrCl₂ produced higher molecular weight backbones, incorporated more hexene-1 and chain branching, and introduced less crystallinity in the copolymers than did Ind₂ZrCl₂. The influence of Ind₂ZrCl₂ on higher-weight homopolymer backbones was opposite to that of Et(Ind)₂ZrCl₂. Incorporation of hexene-1 significantly decreased the average molecular weights and density and increased the run-time-dependent average catalyst activity. A positive comonomer effect took place. The bulk polymer properties did not critically depend on the mixing state. Thermal perturbations broadened the polydispersity index.