Crystallization-Induced Perturbation of Microdomain Morphology in Sphere-Forming Block Copolymer
| Autor: | Hsiu-Chun Li, 李秀君 |
|---|---|
| Rok vydání: | 2002 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 90 This thesis consists of two parts. The first part centers on the studies of the crystalline microdomain (MD) structure in a sphere-forming ploy(ethylene oxide)-block-polybutadiene (PEO—b-PB)/PB blends; the effects of crystallization condition and post-annealing below the melting point have been explored. The second part investigates the crystallization behavior of PEO homopolymer confined within the nanoscaled spherical MDs; such a homopolymer confinement was achieved through a ternary blending of PEO-b-PB with both PEO and PB homopolymers. A cylinder-forming PEO-b-PB was blended with a low molecular weight PB homopolymer to yield the wet-brush type of blends containing PEO spherical MDs in the melt. Crystallizations of PEO blocks within the spherical MDs were induced at the temperatures above the Tg of PB such that the domains were dispersed in a soft matrix during crystallization. The MD structures were then probed by small angle X-ray scattering (SAXS) from which the perturbation in domain structure was resolved through the analysis of the form factor scattering. It was found that the spherical MDs slightly deformed into ellipsoid-like objects with the average aspect ratio of ca. 1.3 upon crystallization. The crystallization-induced MD deformation was further verified through the real-space morphology observed by TEM. The effect of post-annealing on the structure of the ellipsoidal crystalline MDs was also investigated. In this case, the samples having been crystallized at a given temperature was annealed at temperatures below the melting point of PEO. The SAXS profiles and TEM micrographs of the annealed samples showed that the ellipsoidal crystalline MDs transformed into rod-like objects with the average aspect ratio of ca. 2.5 upon annealing. The dimensions of the individual rods exceeded that of the crystalline MDs, suggesting that these crystalline rods were formed through coalescence of 2 ~ 3 crystalline MDs during the annealing process. The MD coalescence, which occurred below the melting point of PEO, may be termed as “sold-solid coalescence”, and its detailed mechanism would deserve further studies. In the ternary PEO-b-PB/PEO/PB blends, the PEO homopolymer has been successfully incorporated into the MDs established by the microphase separation between PEO and PB blocks. This system thus offered an interesting model for investigating the crystallization behavior of homopolymer chains under nanoscaled spatial confinement. In the MDs, the PEO hompolymer did not co-crystallize with the PEO blocks, thereby generating a crystalline-crystalline core-shell structure where the PEO hompolymer crystal formed the core and the shell was constituted by the crystalline PEO blocks. The PEO homopolymer was capable of co-crystallizing with the PEO homopolymer having the same molecular weight as the PEO blocks. Consequently, the “segregated crystallization” in the nanoscaled MDs was interpreted on the basis of the ²connectvity effect” imposed on the PEO blocks by the corona PB blocks, where the tendency of the PB blocks to resist its conformational perturbation introduced by PEO crystallization has effectively prevented the PEO blocks from cocrystallizing with the PEO homopolymer within the MDs. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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