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Phase separation and morphology of diblock and segmented block copolymers
Abstract
Bulk morphologies and microphase separation behavior were studied as a function of composition and temperature for two-component (AB) diblock copolymers and as a function of composition and processing conditions for two-component segmented block copolymers. For the diblock study, well characterized, low molecular weight poly(styrene-isoprene) diblock copolymers (polystyrene volume fractions: 0.21-0.76) were examined with small angle X-ray scattering (SAXS) as a function of temperature to investigate the nature of order-order and order-disorder transitions near the microphase separation transition (MST). Data from these samples was used to develop a comprehensive morphology diagram, near the MST, as a function of $\sb{\chi}$N and composition. These results are compared with MST theories of Leibler and of Fredrickson and Helfand to provide a critical test of their predictions. Near a volume fraction of 0.5, both theories are shown to be relatively accurate, but at compositions far from 0.5 experimental results show that the two blocks are considerably less compatible than has been predicted. The absence of predicted order-order transitions near the MST indicates that composition fluctuation effects are important for low molecular weight diblocks. Further from the MST, an order-order transition was observed in a single sample as a function of temperature. The second study was an investigation of the effect of composition and processing conditions on microphase separation of segmented polyurea block copolymers used for reaction injection molding (RIM). Polyurea block copolymers polymerized in a RIM system were compared with solvent-cast solution polymerized polyureas of the same compositions (hard segment weight fractions: 0.11-0.66) to examine the effect of processing conditions. The Debye correlation function model, which assumes a random two-phase structure with no long or short range order and randomly shaped domains, was found to fit the SAXS data for the entire series of polyureas very well. Except at the highest hard segment content, the degree of phase separation, measured from the SAXS invariant, was higher for the RIM materials than the solution polymerized polyureas. This higher degree of phase separation correlates well with the better mechanical properties of the RIM samples.
Subject Area
Polymers|Materials science
Recommended Citation
Gobran, David A, "Phase separation and morphology of diblock and segmented block copolymers" (1990). Doctoral Dissertations Available from Proquest. AAI9101634.
https://scholarworks.umass.edu/dissertations/AAI9101634