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ORGANOCLAY NANOCOMPOSITES BASED ON VINYLPYRIDINE-CONTAINING BLOCK COPOLYMERS
Zha, Weibin

2006, Doctor of Philosophy, University of Akron, Polymer Engineering.
The order-disorder transition temperatures (TODTs) of three polystyrene-block-poly(2-vinylpyridine) (S2VP diblock) and three polystyrene-block-poly(4-vinylpyridine) (S4VP diblock) copolymers were determined using oscillatory shear rheometry and small-angle X-ray scattering (SAXS). It has been found that for comparable molecular weight and block composition, the TODT of S4VP diblock copolymer is exceedingly high compared with that of S2VP diblock copolymer. The experimental observation has been confirmed by theoretical predictions from currently held mean-field theory. To find the origin of the difference in TODT between S2VP and S4VP diblock copolymers, thermally stimulated current (TSC) method and dielectric relaxation spectroscopy were employed to investigate differences in polarizability between S2VP and S4VP diblock copolymers. Organoclay nanocomposites based on S2VP diblock copolymers and polystyrene-block-polyisoprene-block-poly(2-vinylpyridine) (SI2VP triblock) copolymers were prepared using solution blending and melt blending. The dispersion characteristics of these nanocomposites were investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). In addition, the morphology of the block copolymer in the nanocomposites has been investigated using TEM and SAXS. TSC method was used to find evidence that exfoliation of organoclay aggregates in the polymer matrix is attributable to the presence of ion-dipole interactions between the positively charged N+ ion in the surfactant residing at the surface of organoclay and the dipoles of 2-vinylpyridine ring in the poly(2-vinylpyridine) (P2VP) block. The nanocomposites based on low-molecular-weight block copolymers containing a small amount of P2VP block (S2VP-5, SI2VP-5, SI2VP-13) were found to give rise to a very high degree of dispersion of organoclay aggregates, irrespective of the chemical structure of the surfactant residing at the surface of the organoclay and the preparation method employed. As the amount of P2VP block in S2VP was increased from 5 to 25 and to 56 wt %, the resultant nanocomposites were found to give rise to a low degree of dispersion of organoclay aggregates. For nanocomposites based on high-molecular-weight block copolymers, it was observed that the aggregates of Cloisite 30B (Southern Clay Products) underwent exfoliation during solution blending, while the aggregates of Cloisite 15A (Southern Clay Products) underwent exfoliation during melt blending. It has been found that the melt blending temperature relative to the TODT of a block copolymer plays a decisive role in determining whether melt-blended nanocomposites would have exfoliated or intercalated organoclay aggregates. Very interestingly, both TEM and SAXS studies indicate that microphase separation was induced from a disordered diblock copolymer (SI2VP-5) by the presence of an organoclay, and the core-shell cylindrical microdomains of a neat triblock copolymer (SI2VP-13) transformed into lamellae after the block was mixed with an organoclay. The linear dynamic viscoelastic behaviors of the organoclay nanocomposites prepared in this study also have been investigated. We have found that isochronal dynamic temperature sweep experiments provide very useful, though qualitative, information on the dispersion characteristics of organoclay nanocomposites.
Chang Dae Han (Advisor)
218 p.

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Zha, W. (2006). ORGANOCLAY NANOCOMPOSITES BASED ON VINYLPYRIDINE-CONTAINING BLOCK COPOLYMERS. (Electronic Thesis or Dissertation). Retrieved from https://etd.ohiolink.edu/

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Zha, Weibin. "ORGANOCLAY NANOCOMPOSITES BASED ON VINYLPYRIDINE-CONTAINING BLOCK COPOLYMERS." Electronic Thesis or Dissertation. University of Akron, 2006. OhioLINK Electronic Theses and Dissertations Center. 26 May 2015.

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Zha, Weibin "ORGANOCLAY NANOCOMPOSITES BASED ON VINYLPYRIDINE-CONTAINING BLOCK COPOLYMERS." Electronic Thesis or Dissertation. University of Akron, 2006. https://etd.ohiolink.edu/

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