Structure and Dynamics of Polymer Blends Exhibiting Strong Intermolecular Interactions

The first objective of this effort is a quantitative investigation of crystallization and structure formation in model polymer blends directly at the lamellar level, using tapping mode atomic force microscopy. A number of questions that are key to developing a complete understanding of polymer crystallization, in the neat state and in melt-miscible blends, will be addressed. For example, does lamellar growth proceed uniformly, or are local growth rates time-dependent and variable from lamella to lamella? How are the answers to this and other fundamental questions influenced by the presence of a high Tg, amorphous polymer diluent? To supplement the experimental work, findings will be compared with predictions of a finite element model. The second objective of the project is to develop insight into the dynamics of miscible polymer blends exhibiting intermolecular hydrogen bonding, as probed by dielectric spectroscopy. There has been little research in this area, particularly with respect to the influence of intermolecular interactions on the fragility of the glassy state and the dynamics of hydrogen bonding. The motivation for this work was partly shaped by current interest in thermoreversible networks and hydrogen-bonded, self-assembling supramolecular structures. The focus of the dielectric experiments will be on model binary blends of copolymers in which the number of intermolecular hydrogen bonds can be systematically varied by changing copolymer composition. Certain blends in this study will satisfy the assumptions of the LRC model for the dynamics of reversible networks, and will provide a good test of the model. Finally, with the support of an NSF - MRI grant, a hybrid instrument is under development that will be capable of performing simultaneous dielectric and two-dimensional infrared spectroscopic measurements. This new instrument will undoubtedly have an important impact on the research described above.

The results of this research will have broad impact on our understanding of both crystalline polymers and polymer blends, areas of great importance in the industrial sector. In addition to the direct educational impact on graduate and undergraduate students involved in the research activity, research results will be incorporated into graduate level courses taught by the PI. Research findings will be disseminated through publication in peer-reviewed journals, as well as through presentations by the PI and group members at major scientific meetings.