Cooperative Molecular Motions in Glassy Polymers

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The aim of the research is to address the nature of sub-Tg relaxations in some high-temperature glassy polymers. The relaxation behaviors of polycarbonates and other rigid aromatic backbone glassy polymers will be investigated. The low-temperature relaxation of bisphenol-A polycarbonate has an extensive in-chain cooperative character. This cooperative motion is thought to be the key to polycarbonate's superior mechanical properties. The origin of this in-chain cooperativity and the relaxation behavior of other kinds of glassy polymers can be better understood by using tailored molecular architectures together with dynamic mechanical measurements. Once the origin of cooperative motion is understood, an important question will be answered: How does the scale of this cooperative motion affect intermolecular interactions? Dynamic bulk relaxation experiments will be used to address this question. Another question to be answered in the proposed research deals with how the scale of cooperative motion affects the mechanical properties of the polymer in terms of ductility and brittleness. Through this research, the relationships between molecular structure, relaxation and mechanical properties will be further clarified and the results can be used as guidelines to design and synthesize new high-temperature ductile polymers with desirable properties.