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A spectroscopic study of phase transitions in polymers
Abstract
In this study three examples of solid-solid phase transitions in polymers have been investigated with vibrational spectroscopy. The effects of a high strength electric field on the microstructure of piezoelectric copolymers of vinylidene fluoride and trifluoroethylene has been studied. The application of an electric field is found to produce changes in dipolar orientation and also changes in chain conformation, and these are measured by infrared spectroscopy below and above the Curie transition temperature. Electrical poling behavior is examined for two copolymer compositions which show substantial differences in structure and Curie temperature, and infrared analysis provides a means to determine the differences in dipole orientation and chain conformation distribution for these two copolymers. Infrared spectroscopy is employed to determine the content of $\alpha$ and $\beta$ phases of PVDF for two highly drawn blends and also for PVDF homopolymer. The effects of annealing on the phase content and segmental orientation are measured. Highly drawn PVDF samples are used for determination of the transition dipole moment directions of selected vibrational bands. The microstructure of different phases of syndiotactic polystyrene has also been studied. A normal coordinate analysis is performed for the all trans conformation of syndiotactic polystyrene using nonredundant coordinates and force constants for the phenyl ring. Force constants for the chain have been obtained from studies of saturated hydrocarbons. Assignment of the infrared and Raman bands and their polarization characteristics is made upon comparison of the calculated results with the observed spectra obtained from coextruded films. Annealing the coextruded films increases the overall segmental orientation as the crystallinity increases. The theoretical modulus of a single chain has been calculated from the dispersion curive of the longitudinal acoustic branch near the Brillouin zone center. The kinetics of the irreversible phase transition in syndiotactic polystyrene has been measured as a function of temperature and annealing history, in order to determine the effect of thermal history on the transition behavior. (Abstract shortened with permission of author.)
Subject Area
Plastics|Materials science
Recommended Citation
Reynolds, Nicholas Matthew, "A spectroscopic study of phase transitions in polymers" (1990). Doctoral Dissertations Available from Proquest. AAI9100531.
https://scholarworks.umass.edu/dissertations/AAI9100531