A series of HDPE resins having a relatively narrow molecular weight distribution and a well-defined degree of sparse long-chain branching, LCB, are evaluated to determine if their rheological properties are consistent with the predictions of the McLeish-Larson pom-pom model. Rheological analysis and parameter fitting with a multi-mode McLeish-Larson pom-pom model provides a molecularly sensitive set of model parameters and gives insight to molecular structure. Rheological testing includes small-amplitude oscillatory experiments to extract the backbone orientation relaxation time, τbi, and the corresponding fraction of stress that is relaxing, gi; extensional stress growth experiments to determine the backbone stretch relaxation time, τsi, and the number of dangling branch arms, qi; and jump-strain experiments for the proposition of a new method to determine τsi based on separation in the relaxation modulus curves at short timescales. On the short timescales there is a separation of values for the relaxation times associated with the stretch relaxation parameter whereas, on longer timescales the relaxation modulus is observed to be separable in time and strain, which is consistent with the predictions of the model. The new technique for the determination of τsi is verified by the accuracy with which uniaxial extensional data is fit. Rheological analysis provides an opportunity to evaluate the ability of the pom-pom model to describe well-defined systems of materials with minimal differences in LCB concentrations and to determine the consistency of the model to correctly predict the levels of LCB present. Analyses of processing characteristics provide a more practical, industrially relevant representation of the influence of LCB. An extension to film-casting characteristics by measuring the evolution of the film width, necking, as well as distribution of the film thickness, edge-bead formation, reveals the production of more usable film with higher levels of LCB.

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