The independent and combined effects of long and short chain branching on the thermorheological behavior of polyethylene are described. The activation energy of linear poly(ethylenebutene) increases with butene content to approximately 33-34 kJ/mol and then levels off for butene contents between 7 and 25 wt %. Long chain branched homo-polyethylene is thermorheologically complex and is most sensitive to temperature at low frequency. A technique for determining the activation energy spectra of thermorheologically complex materials is proposed. Short and long branches in the same system synergistically increase the zero-shear rate activation energy.

Polymeric nanocellular foams are broadly defined as having cell size below one micron. However, it is only when cell size reaches 100 nm or less that unique thermal conductivity, dielectric constant, optical, or mechanical properties are expected due to gas confinement in the cells or polymer confinement in the cell walls. Producing such materials with low density by physical foaming with CO 2 requires the controlled nucleation and growth of 10 15 210 16 cells/cm 3 . This is a formidable challenge that necessitates new foaming strategies. This review provides a description of processes, conditions, and polymer systems that have been employed over the past 15 years to achieve increasingly higher cell densities and expansion ratio, culminating with the recent development of low density nanofoams and of nanostructured polymers in which nucleation can be precisely controlled. Remaining barriers to scale-up are summarized.

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.

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We propose a density-functional theory (DFT) describing inhomogeneous polymer-carbon dioxide mixtures based on a perturbed-chain statistical associating fluid theory equation of state (PC-SAFT EOS). The weight density functions from fundamental measure theory are used to extend the bulk excess Helmholtz free energy to the inhomogeneous case. The additional long-range dispersion contributions are included using a mean-field approach. We apply our DFT to the interfacial properties of polystyrene-CO 2 and poly(methyl methacrylate) CO 2 systems. Calculated values for both solubility and interfacial tension are in good agreement with experimental data. In comparison with our earlier DFT based on the Peng-Robinson-SAFT EOS, the current DFT produces quantitatively superior agreement with experimental data and is free of the unphysical behavior at high pressures (>35 MPa) in the earlier theory.