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1. Spectroscopic investigation of crystal morphology in semicrystalline polymers. 2. Spectroscopic investigation of restricted geometries in monolayers of adsorbed polymers
Abstract
The highly ordered long range structure associated with the crystalline core of semi-crystalline linear aliphatic polyesters, is evaluated using Raman spectroscopy. Polarization modulation reflection infrared spectroscopy, and x-ray photoelectron spectroscopy, are utilized to determine the degree of structural and chemical anisotropy in ultra thin glassy polymer films formed by monolayer chemisorption of functionalized polystyrene onto external surfaces. In both cases the morphological characterization is restricted to the determination of polymer structure in regions that are on the order of 100 angstroms or less in thickness. The frequency of the longitudinal acoustic mode (LAM-1) normal mode vibration is inversely related to the crystal stem length. It is found in the very low frequency region of the Raman spectrum for these linear aliphatic polyesters. It is utilized to directly determine the crystal thickness, the distribution of crystal stem lengths, and the longitudinal Youngs modulus. The existence of multiple low frequency components is studied as a function of degree of supercooling, monomer chemical structure, crystal packing, and crystal thickening. Polarization modulation reflection infrared measurements, and a segmental orientation model based solely upon relative intensities, are used to determine the average chain axis orientation relative to the surface normal for sulfur functionalized polystyrenes adsorbed to Au surfaces. The orientation of the polystyrene chain is higher for the PS$\sb{95}$-PPS$\sb5$ adsorbed film (0.29) than for the thiol endcapped polystyrene (0.22). The higher copolymer orientation can be attributed to the slightly longer strongly interacting part of the structure. The block is sufficiently long to enable a higher grafting density. Results for other copolymers indicate that a structural transition occurs in the adsorbed copolymer films between 95:5 and 90:10 molar ratios, for a degree of polymerization around 600. The transition from anisotropic to an isotropic polystyrene conformation is related to the XPS film thickness, and thus the grafting density. Segregation in the chemical composition exists as shown by XPS. The degree of segregation is related to the propylene sulfide block length relative to the overall degree of polymerization. If the interaction strength is sufficiently large then a critical block length will exist which will determine whether the buoy structure can form an oriented brush in solution and a collapsed oriented ultra thin film.
Subject Area
Polymer chemistry|Materials science|Physical chemistry|Chemistry
Recommended Citation
Waldman, David Allen, "1. Spectroscopic investigation of crystal morphology in semicrystalline polymers. 2. Spectroscopic investigation of restricted geometries in monolayers of adsorbed polymers" (1990). Doctoral Dissertations Available from Proquest. AAI9035415.
https://scholarworks.umass.edu/dissertations/AAI9035415