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A spectroscopic analysis of the structure of highly ordered polymers
Abstract
The structure, morphology, phase transition behavior, and factors which govern the formation of helical crystalline syndiotactic polystyrene (sPS) have been investigated. The primary technique employed is vibrational spectroscopy, proven useful to obtain chain conformation distribution and chain and segmental orientation of polymers. Other techniques, such as wide angle X-ray diffraction and thermal analysis are used to characterize the crystalline state. Highly crystalline helical (TTGG) sPS has been prepared by isothermal growth from dilute solution, minimizing the amorphous structure. The crystals are observed to consist of a complexed structure of sPS and solvent molecules. Low frequency Raman spectra for sPS and their solvent complexes are reported. Although intramolecular, the phenyl ring torsion about the backbone is observed to be highly sensitive to the solvent complexed crystalline state and therefore the intermolecular ring environment. This suggests that such a band may be useful for examining the polymer-solvent specific interaction spectroscopically and therefore the mechanism of formation of the helical crystalline phase in sPS. The morphology of as-grown highly crystalline sPS/ethylbenzene mats consists of ribbon-like structures, which are irreversibly disrupted upon the expulsion of solvent from the crystal lattice. Complete molecular reordering during the helix to trans phase transition cannot be accounted for by cooperative bond rotation, consistent with the irreversible nature of the transition, and further emphasizing the critical role of solvent in the formation of helical crystallites. Crystalline syndiotactic polystyrene/solvent complexes prepared from different solvents exhibit a variety of different structures, as indicated by wide angle X-ray diffraction and thermal analysis. Differences in chain packing associated with these structures are reflected in the band shape and intensity of the low frequency phenyl ring torsional vibration. In addition, polarized infrared spectra show that phenyl rings of solvent molecules pack parallel to the syndiotactic polystyrene phenyl rings in these crystalline syndiotactic polystyrene/solvent complexes. A normal vibrational analysis is performed for the helical (TGGT) form of sPS. The calculated frequencies agree well with the observed infrared and Raman spectra, including conformationally sensitive bands.
Subject Area
Physical chemistry|Polymer chemistry|Chemistry
Recommended Citation
Savage, John David, "A spectroscopic analysis of the structure of highly ordered polymers" (1993). Doctoral Dissertations Available from Proquest. AAI9408340.
https://scholarworks.umass.edu/dissertations/AAI9408340