The goal of this work was to provide a usable framework for describing the molecular structure of long-chain branched, metallocene-catalyzed polyethylene (mPE). This will allow better understanding of structure-property relations for these materials and in the future allow the development of new metallocene based systems with tailor-made properties. In particular, we are interested in the relationship between molecular structure and rheological behavior of polyethylene and therefore represent the structure in terms that are relevant to the rheological properties. To provide an intuitive understanding of the structure, we present a ternary diagram showing clearly the independent variables in the system and allowing a quick analysis of blended systems.

Polymerization of ethylene in a CSTR using a combined metallocene catalyst system (combination of an open-face catalyst, such as Constrained Geometry Catalyst, and a conventional metallocene catalyst) was studied. Using the model developed by Soares and Hamielec, and expanded by Beigzadeh et al., a steady-state simulator was prepared. The effects of different process parameters (such as reactor residence time) and kinetic parameters of the combined catalyst system on steady-state values of molecular weight, polydispersity index, long-chain branching frequency, and copolymer composition (in the case of copolymerization with ␣-olefins) were investigated. It was shown how recipes for synthesizing polyolefins with tailor-made MWD, CCD, and LCB frequencies can be designed.

SUMMARY: The solution polymerization of ethylene in Isopar E in a semi-batch reactor using combined CGC-Ti and Et[Ind] 2 ZrCl 2 catalysts was studied. Methylaluminoxane (MAO) and tris(pentafluorophenyl)borane were used as co-catalysts. Samples were analyzed by 13 C NMR and gel permeation chromatography (GPC) for their branching content and molecular weight distribution. It was shown that there was an optimum ratio of CGC-Ti/Et[Ind] 2 ZrCl 2 that maximizes the number of long-chain branches of the formed polyethylene.

Monte Carlo simulation was used to model the fractionation process in crystallization analysis fractionation (CRYSTAF). Five poly(ethylene/1-octene) samples synthesized with a single-site-type catalyst were used to verify the simulation results. It was proposed that the fractionation mechanism be controlled by the crystallization of the longest ethylene sequence in each chain. Good agreement between experimental and simulation results verified the validity of the proposed fractionation mechanism.

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