Characteristics of Long Chain Branching in Ethene Polymerization with Single Site Catalysts

Linear and long chain branched ethene homopolymers and copolymers with 1-hexene were produced with metallocene catalysts. The presence and absence of long chain branching in the polymers was studied by dynamic rheological and gel permeation chromatography−on-line viscometry analysis. Long chain branched polymers were produced with 1- and 2-siloxy-substituted derivatives of rac-Et(Ind)<INF>2</INF>ZrCl<INF>2</INF>/MAO and MeSi(C<INF>5</INF>Me<INF>4</INF>)(N-t-Bu)TiCl<INF>2</INF>/MAO. As judged by the rheological behavior, n-ButCp<INF>2</INF>ZrCl<INF>2</INF>/MAO produced linear chains, as did the meso form of one of the substituted Et(Ind)<INF>2</INF>ZrCl<INF>2</INF> catalyst structures. The rheological behavior of the polymers was affected by the polymerization conditions, especially by the addition of comonomer and the partial pressures of ethene and hydrogen. In addition, the slurry solvent was relevant to some of the catalysts. The effects of catalyst activity and different mass transfer limitations on the long chain branching were studied. As was evident from the rheological behavior, the long chain branching could be controlled by both the choice of the catalyst and the polymerization conditions. The rheological behavior is discussed with reference to the content of the long chain branches and the structure of the branching.