Ethen/l-Hexen- und 1-Octadecen-Copolymerisation mit dem stereorigiden Zirkon-Katalysatorsystem /Pr(CpFlu)ZrCl2/MAO: Einfluß der Temperatur

P eter H. M ühlenbrock, G erhard Fink* M ax-Planck-Institut für Kohlenforschung, Kaiser-W ilhelm-Platz 1, D-45470 Mülheim an der Ruhr Herrn Professor Dr. Dr. h. c. mult. Günther Wilke zum 70. Geburtstag gewidmet Z. N aturforsch. 50b, 423-429 (1995); eingegangen am 7. O k tober 1994 M etallocenes, E thene/a-O lefin Copolym erization, R ate Enhancem ent Effect, Influence of the Tem perature E thene was copolym erized with 1-hexene and 1-octadecene at d ifferent tem peratures to study the influence of the tem perature. The stereorigid catalyst [2,4-cyclopentadien-l-yliden(/so-propyliden)fluoren-9-yliden]zirconium dichloride /P r(C pFlu)Z rC l2 1 in com bination with m ethylalum oxane MAO was used. The polym erization rate of e thene depends in a wide range on the tem perature and the com onom er content in solution. In each case a large rate enhancem ent at low ratios [com onom er]/[ethene] was observed. A t 25 °C the polym erization rate of ethene increases continuously with increasing [l-hexene]/[ethene]-ratio . A t 40 °C the consum ption of ethene is nearly independent of the 1-hexene conten t in solution. Finally, at 60 °C, similar to the ethene/l-octadecene-copolym erisation at d ifferent tem peratures, the polym erization rate of ethene decreases with increasing [l-hexene]/[ethene]-ratio . It is sug­ gested that this behavior is caused by the mobility of the side chains in the copolym er near the active center, probably for sterical reasons. W ith increasing tem peratures, the side chain becom es more and more flexible and thus the sterical hindrance is increased. This effect is even stronger with long chain a-olefins. The m icrostructure of the copolym er was investigated with respect to M arcovian statistic 1. and 2. order. The experimental triad distribution is described satisfactorily only with the second order statistic. Independent of the tem perature the r22 param eter is considerably greater than the r 12 param eter, the insertion of an a-olefin thus being more favored for the sequence {R-(a-olefine)-(a-olefine)-Kat.} than for {R-(ethene)-(a-olefine)-K at.}. It therefore appears that both last inserted m onom ers influence the insertion of the subsequent m onom er, especially at high com onom er contents. Furtherm ore, the param eters for the a-olefin inser­ tions r22 and r 12 are nearly independent of the tem perature of polym erization, w hereas the r n and r21 param eters increase with increasing tem perature.