Characteristics of long chain branching in ethene polymerization with single site catalysts

Linear and long chain branched ethene homopolymers and copolymers with l-he xene 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 bran ched polymers were, produced with 1- and 2-siloxy-substituted derivatives o f rac-Et-(Ind)(2)ZrCl2/MAO and MeSi(C5Me4)(N-t-Bu)TiCl2/MAO. As judged by t he rheological behavior, n-ButCp(2)-ZrCl2/MAO produced linear chains, as di d the meso form of one of the substituted Et(Ind)(2)ZrCl2 catalyst structur es. The rheological behavior of the polymers was affected by the polymeriza tion conditions, especially by the addition of comonomer and the partial pr essures of ethene and hydrogen. In addition, the slurry solvent was relevan t 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 co ntrolled by both the choice of the catalyst and the polymerization conditio ns. The rheological behavior is discussed with reference to the content of the long chain branches and the structure of the branching.