Morphology Development Associated With Polymer Blends
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Morphology Development Associated With Polymer Blends Tomoko Hashida, Ying Hua, and Shaw Ling Hsu Polymer Science and Engineering Department and Material Research Science and Engineering Center, University of Massachusetts, Amherst, MA 01003, U.S.A. Charles W. Paul National Starch & Chemical, Bridgewater, NJ 08807, U.S.A. ABSTRACT Morphology development of crystallizable polymer blends has been investigated using optical microscopy, thermal analysis, and vibrational spectroscopy. The blends studied involve crystallizable polyesters of poly(hexamethylene adipate) (PHMA) and poly(hexamethylene sebacate) (PHMS) and non-crystallizable poly(propylene glycol) (PPG). Although these polyesters possess similar chemical structure, they exhibit different phase behavior. Ternary blends including a high glass transition temperature (Tg) component were also studied. Crystallization kinetics in these blends was obtained utilizing Fourier transform infrared spectroscopy. Micro-Raman spectroscopy capable of achieving high spatial resolution (1 µm2) revealed detailed morphological differences in the phase-separated structures. This technique made possible for the first time characterization of the chemical composition of the blends and distribution of crystallites. The role of the third relative immobile component significantly changed both chemical distribution and the degree of crystallinity. INTRODUCTION Morphology development of polymer blends involving a crystallizable component is extremely complicated. Phase separation and crystallization occur simultaneously. The crystallization process, the central focus of this study, is dependent on the local concentration of the crystallizable component and the segmental mobility necessary for growth to occur. Many aspects of the crystallization process in blends have been investigated. For example, optical microscopic studies have been used to characterize crystallization kinetics.1 Thermal analyses have elucidated the extent of crystallization.2 The measured melting temperatures have often been correlated to the interaction parameter governing mixing behavior.3 No studies have established the relationship between local composition and crystallization kinetics. In this study, a number of binary and ternary blends were investigated. Crystallization kinetics of miscible and immiscible blends was compared and morphological features in terms of domain size and their dispersion characterized. The crystallization kinetics of the overall sample was measured. Most importantly, localized compositions of various binary and ternary blends were elucidated. The localized composition was found to control crystallization kinetics. This observation is not surprising given the fact that nucleation must depend on local concentration of the crystallizable component. In addition, the growth process must depend on segmental dynamics. Information relating these fundamental issues to the crystallization process in polymer blends has, however, been unavailable.
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The localized polymer compos
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