COPOLYMERIZATION OF ETHENE 1-DODECENE AND ETHENE 1-OCTADECENE WITH THE STEREORIGID ZIRCONIUM CATALYST SYSTEMS IPR[FLUCP]ZRCL2 MAO AND ME(2)SI[IND]2ZRCL2 MAO - INFLUENCE OF THE COMONOMER CHAIN-LENGTH

Ethene was copolymerized with 1-dodecene and 1-octadecene to study the influence of the comonomer chain length on the rate enhancement effec t where the catalyst system was stereorigid iPr-[FluCp]ZrCl2 (I) or Me (2)Si[Ind]2ZrCl2 (II) combined with methylaluminoxane (MAO). With cata lyst II and both of the comonomers the polymerization rate of ethene i ncreased 2.5-fold before starting to decrease above the [comonomer]/[e thene] ratio of 1. With catalyst I the situation was different. With 1 -octadecene the maximum in the curve of the polymerization rate of eth ene was again at [comonomer]/[ethene] = 1. With 1-dodecene, on the oth er hand, the consumption of ethene, instead of decreasing, continued t o increase above the [1-dodecene]/[ethene] ratio of 1. The different b ehavior with two catalysts and comonomers perhaps is explained by the gap aperture between the pi-ligands of the two catalysts and the steri c conditions at the catalytic center: the longer the comonomer, and th e narrower the gap aperture, the more difficult it is for the ethene m onomer unit to insert itself and the ethene propagation reaction becom es slower. The microstructure of the copolymers was investigated with Markovian first- and second-order statistics. The experimental triad d istributions can satisfactorily be described with the second-order sta tistics. The r(22) and r(12) parameters obtained show that catalyst I copolymerizes alpha-olefins better and that, for the same catalyst, th ere is no marked difference in the values obtained with 1-dodecene and 1-octadecene. Furthermore, the r(22) parameters were considerably gre ater with 1-dodecene and 1-octadecene than with 1-hexene. Evidently, a block of the long chain alpha-olefin opens the gap aperture between t he pi-ligands, facilitating insertion of an alpha-olefin. The addition of 1-butene decreased the reactivity of the higher alpha-olefin: the comonomer content decreased to half with catalyst I and to two-thirds with catalyst II when the 1-butene concentration was increased from 0 to 1 mol/dm(3). Apparently, the synergistic effect works only with het erogeneous catalyst systems and not at all with the homogeneous metall ocenes.