Structure and Relaxation Processes in Polymers

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9630061 Boyd The general goal of this research is to develop a better understanding of relaxation processes, especially at the molecular level. Two approaches are to be used. One takes advantage of the impressive ability developed recently for carrying out molecular level computer simulations of the structure and dynamic processes in bulk, dense-packed polymers. The other approach is experimental and employs the dielectric relaxation technique to locate and characterize relaxation processes. Part of the simulation effort will be directed toward developing a better molecular understanding of the melt to glass transition process. Our recent research showed that as the glass forms the dynamic processes become spatially heterogeneous. Molecular dynamics (MD) simulations are to be used to characterize the local structure and relate it to the chain dynamics. This will be done both in polymers that possess subglass relaxations and those that do not. In a more practical vein, the simulations will be used to develop structure- property understanding of the connection between the glass transition temperature and chemical structure. In fact the use of MD simulations to predict Tg values from the polymer chemical structural formula will be pursued. Dielectric measurements will be used to generate better data for comparison with the MD results. Liquid crystalline polymers (LCPs) are an intermediate case between the broad classes of amorphous and crystalline polymers. MD simulations are to be applied to main-chain thermotropic LCPs in order to better understand the relaxation processes that occur in them. Another class of LCP concerns the case where the mesogenic unit is incorporated in a side-chain. Dielectric studies are to be carried out to characterize the relaxations in side chain mesogenic LCPs. %%% Polymeric materials form one of the cornerstones of modern technology. Amorphous polymers, both as glasses and as elastomers, comprise an important compone nt of these materials. Their behavior as materials, including differentiating between their glassy or elastomeric behavior, is largely determined by the presence and associated time temperature location of relaxation processes. In turn, relaxation processes have their source in molecular motions of various types. ***