Polyolefins comprise an economically and technologically important class of materials. As a subset of all polymers, they are in general well-known, but continuing improvements in metallocene polymerization catalysis have demonstrated that enhanced physical properties are accessible through copolymerization, blending, and composites. Consequently, polyolefins and their blends span the gamut of possible applications, ranging from low-cost disposable foodpackaging to multicomponent composites for aerospace structural design. In all cases involving more than just a pure polymer, which is the majority, the morphology and local structure of the blend or composite determines the final physical and performance properties of the material. Surprisingly, first-principle mixing rules for polyolefin blends are not known, as these chemically simple polymers defy like dissolves like solubility conventions. Intellectual Merit. A conspicuous lack of experimental data at the molecular or chain level suggests that chain-structure/miscibility relationships in bulk polyolefin mixtures are far from being realized. The microscopic to mesoscopic (i.e. angstroms to tens of nanometers) length scales accessible by solids NMR experiments can address this deficiency in a non-invasive manner. Through acquisition of the chain-specific data (dynamics and distance) needed to resolve long-standing questions about the relative importance of chain packing and chain architecture, the role of each in determining entropic versus enthalpic contributions to the overall phase behavior may be examined. Broader Impact. The fundamental scientific questions surrounding polyolefin phase behavior, particularly for amorphous polyolefins in the melt or solid states, are far reaching in that mixtures of these nonpolar, noncrystalline polymers constitute a limiting class of macromolecular thermodynamics. As such, polyolefins and their blends are ideal systems for the experimental study of some long-standing questions in polymer science. For example, bulk amorphous polyolefins are concentrated systems, with many degrees of freedom. Given the varying chain architectures possible with polyolefins, can distinct degrees of freedom within and between molecules (rational introduction of dynamic heterogeneity fluctuations) be identified and related to phase behavior/phase transitions? The length-scale and time-scale of phase transitions in amorphous macromolecules, like those in liquid crystals, have been described in the context of configurational entropy arguments. Can we, using bulk polyolefins and their blends, provide non-invasive experimental confirmation of this view at the local chain level (1- 10 nm)? If glass formation in non-interacting molecules is driven by loss of configurational entropy, can molecular level (less than the polymer radius of gyration) experiments detect and define local Tg's? Can this data be used to help broaden the scope of current thermodynamic models of polymer phase behavior to include configurational entropy contributions? The PI has been, and will continue to be, an active participant at all levels of education through this project. The PI, whose efforts are leveraged through the public outreach director in the NCSU chemistry department, has presented multiple demonstrations in physical science, and polymer science, at elementary, middle, and high school venues. Moreover, the multidisciplinary aspect of this project (spectroscopy, polymer chemistry, polymer physics, materials science) continues to attract top undergraduate and graduate students in the department.
