The bivariate, or cross branching distribution of a gas-phase produced, film-grade ethylene 1-hexene copolymer with enhanced Elmendorf tear in machine direction, MD, and in transverse direction, TD, (> 400 g/mil) and high dart impact has been characterized through the analysis of fractions obtained by molecular weight and 1-hexene composition. The molecular weight fractions, obtained by a solventnon-solvent fractionation technique, are each mixtures of molecules with at least two different 1-hexene compositions, one component with a constant relatively high density ($1 mol% hexene) and a second of a lower density broadly distributed along the molecular weight fractions. The content of the low density component increases with increasing molecular weight of the fraction while the level of 1-hexene decreases. The mixed compositional character of these fractions is easily inferred by their high crystallization rates and both high melting and crystallization temperatures compared to the values of model random ethylene copolymers. The set of compositional fractions obtained by TREF display an increasing 1-hexene concentration with increasing molecular weight, and except for the highest molecular weight components (Mw > 150,000 g/mol) their melting and crystallization behavior followed the random pattern. Higher than expected melting temperatures and a constancy of the high melting temperature peak with increasing crystallization temperature, suggests that the intra-chain 1-hexene distribution of the highly branched, high molecular weight fraction deviates strongly from the random behavior. These structural features and the bimodal character of the composition distribution of this resin, that contains high molecular weight chains with both low and high 1-hexene contents, are correlated with the enhanced key film properties.
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