結晶性嵌段共聚物摻合物與奈米複合材料之自組織行為研究

Self-Organization Behavior of Crystalline Block Copolymer Blends and Nanocomposites

朱哲毅(Che-Yi Chu)

指導教授 ： 陳信龍

國立清華大學/工學院/化學工程學系/博士(2011年)

https://doi.org/10.6843/NTHU.2011.00216

摘要

Diblock copolymers are known to be able to self-assemble into a variety of long-range ordered nanostructures due to the segregation between the repulsive block chains. Depending on the crystallizability of the constituting blocks, diblock copolymers can be classified into amorphous-amorphous, crystalline-amorphous, and crystalline-crystalline diblocks. This thesis is concentrated on studying the unique self-assembly and crystallization behavior of the former two diblock systems.

For amorphous-amorphous diblock coplymers, here we report the existence of a stable ordered bicontinuous double diamond (OBDD) structure in a diblock copolymer composing of a stereoregular block. A slightly asymmetric syndiotactic polypropylene-block-polystyrene (sPP-b-PS) as cast from xylene was found to display OBDD morphology. When the OBDD-forming copolymer was heated, this structure transformed to a gyroid phase at ca. 155 oC. Interestingly, OBDD was recovered upon cooling, indicating that it was a thermodynamically stable structure for sPP-b-PS, which was in contradiction to the conventional view (i.e. OBDD has always been considered as an unstable structure relative to gyroid for block copolymers). We propose that the larger free energy cost encountered in OBDD due to the larger packing frustration may be compensated sufficiently by the release of free energy due to locally ordered packing of the conformationally ordered segments of sPP blocks and thereby stabilized the OBDD structure at the lower temperatures.

The crystallization behavior of the binary blends of two crystalline-amorphous diblock copolymers bearing chemically identical amorphous block was systematically explored in this thesis. Two sub-systems were studied, namely, (1) blend of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and polystyrene-block-poly(L-lactide) (PS-b-PLLA) and (2) blend of isotactic polypropylene-block-polystyrene (iPP-b-PS) and syndiotactic polypropylene-block-polystyrene blends (sPP-b-PS). PEO and PLLA blocks are chemically different, while, iPP and sPP blocks have the same chemical composition but differet stereochemistry. In the melt stat, PEO and PLLA blocks (and iPP and sPP blocks) formed the lamellar microdomains by the cosurfactant effect. It was found that the constraint imposed by the junction points localized at the lamellar interface and the nanoscale confinement effect significantly perturbed the crystallization behavior comparing to their corresponding homopolymer blends. The highly defective PLLA and sPP crystalline domains were formed in which the crystalline stems were intervened by the PEO and iPP chains, respectively. Furthermore, the originally immiscible iPP and sPP homopolymers in the melt were found to become a miscible binary pair in the corresponding diblock copolymers with PS. This may be attributed to that the entropic gain from the moving of the junction points at the interface and the mixing of iPP and sPP blocks in the microdomains may effectively compensate the slightly positive enthalpy of mixing arising from the repulsion between iPP and sPP.

Finally, we showed that the polymerization rate strongly affected the nanoparticle dispersion in the SiO2/PMMA nanocomposite derived by mixing the surface-modified SiO2 nanoparticles with MMA monomer. At slower polymerization, smaller clusters of nanoparticles were formed in which the SiO2 nanoparticles were more densely packed. Contrarily, the particles formed larger clusters in which the interparticle distance became larger at faster polymerization rate. The entropic effect arising from the growing PMMA chains might play an important role governing the final dispersion state of SiO2.

關鍵字

結晶 ； 嵌段共聚物摻合物 ； 高度缺陷晶體 ； ordered bicontinuous double diamond (OBDD) ； gyroid ； order-order transition ； 具立體規則性結構的嵌段共聚物 ； 奈米粒子 ； 奈米複合材料 ； 分散形態

並列摘要

無資料

並列關鍵字

crystallization ； block copolymer blends ； highly defective crystals ； ordered bicontinuous double diamond (OBDD) ； gyroid ； order-order transition ； stereoregular block copolymer ； nanoparticles ； nanocomposites ； dispersion state

參考文獻

(1)Roe, R. J. and Zin, W. C. Macromolecules 1984, 17, 189.

(3)Bates, F. S.; Fredrickson, G. H. Annu. Rev. Phys. Chem. 1990, 41, 525.

(5)Matsen, M. W.; Bates, F. S. Macromolecules 1996, 29, 1091.

(12)Anderson, D. M.; Thomas, E. L. Macromolecules 1988, 21, 3221.

(14)Olmsted, P. D.; Milner, S. T. Phys. Rev. Lett. 1994, 72, 936.