Multilayered supramolecular structures: Two-dimensional polymers and polar assemblies
Le Bonheur, Vassoudevane
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https://hdl.handle.net/2142/19550
Description
Title
Multilayered supramolecular structures: Two-dimensional polymers and polar assemblies
Author(s)
Le Bonheur, Vassoudevane
Issue Date
1996
Doctoral Committee Chair(s)
Stupp, Samuel I.
Department of Study
Materials Science and Engineering
Discipline
Materials Science and Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Polymer
Engineering, Materials Science
Language
eng
Abstract
This research project investigated the structure and properties of bulk films created from multilayered supramolecular structures. The rodcoil molecule was key to the formation of two-dimensional layers stacked over macroscopic distances. It consists of a rigid and monodisperse rod-like segment covalently attached to a flexible coil-like segment. The coil-like segments were of narrow molecular weight distribution and contained a diblock sequence of oligomeric styrene and isoprene. Two rodcoil systems were investigated in this project, one contained a liquid crystalline mesogen and a second one contained a rod functionalized with a phenolic end group. We found that the first rodcoil forms long range layered assemblies in solution cast bulk films with nanophase separation of the three chemically distinct segments. These assemblies stack spontaneously on solid substrates over macroscopic distances and form self-assembled surfaces. Moreover, the substrate seems to guide the stacking direction of the layers. Upon thermal crosslinking of the isoprene middle sector, these assemblies yield 2D polymers which should be shape-persistent plate-like molecules. Isolated 2D polymers are stable up to 320$\sp\circ$C, which is at least 143$\sp\circ$C higher than the isotropization temperature of their precursor monomer.
Rodcoil molecules containing phenolic end groups were found to spontaneously form multilayered supramolecular architectures and up to 40% of the oligoisoprene segments could be crosslinked in these layered structure. Polymerized material formed ordered structures that were stable up to 440$\sp\circ$C. The morphology of polymerized bulk films, about 1 $\mu$m thick, were analyzed by X-ray and ultramicrotomy TEM, and revealed long range spatial order of highly defined lamellar morphology throughout the film. Interestingly, these layers corresponded to a head-to-tail polar stacking of the molecules. Additional proof for this unusual polar stacking was obtained by TEM, analysis of surface properties, and nonlinear optical experiments. Bulk films of these rodcoils were also found to spontaneously form two chemically different surfaces, one hydrophobic and one hydrophilic. Very importantly, a hydrophilic phenolic surface could be generated spontaneously at the air/film interface by casting in a humid environment. Finally, stability tests in corrosive acidic environments and single-lap shear tests revealed that polymerized films exhibit excellent adhesive properties. These findings are possibly the first example of a bulk material with polar assembly and self-organized surfaces.
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