Liquid crystalline multi-block copolymers
Lyotropic and thermotropic high strength liquid crystalline polymers have become an important area of research and development in polymeric, high performance materials. These materials have afforded excellent high temperature stability and high strength in the oriented direction, but not in the tra...
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| Format: | Others |
| Language: | en |
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Virginia Tech
2014
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| Online Access: | http://hdl.handle.net/10919/37872 http://scholar.lib.vt.edu/theses/available/etd-05222007-091335/ |
| Summary: | Lyotropic and thermotropic high strength liquid crystalline polymers have become an important area of research and development in polymeric, high performance materials. These materials have afforded excellent high temperature stability and high strength in the oriented direction, but not in the transverse direction. Hence, "balancing" the properties in both directions is an important area of research.
Segmented polymers composed of an amorphous, glassy engineering thermoplastic, and an anisotropic, liquid crystalline polymer were synthesized and investigated. The isotropic phase is based upon a ductile poly(arylene ether sulfone), while the anisotropic segment is based on a rigid poly(arylate) moiety.
The difunctionally terminated, controlled molecular weight poly(sulfone) oligomers were synthesized via a nucleophilic aromatic substitution reaction. Functional end groups included phenolic, acetate and carboxyl. The structure and reactivity of these oligomers was characterized by analytical techniques, including FT-IR, NMR, and polymer physical characterization methods such as, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), and thermal mechanical analysis (TMA), and dynamic mechanical thermal analysis (DMTA).
The well characterized, difunctionally terminated poly(sulfone) oligomers were then utilized along with ester forming monomers in a subsequent melt acidolysis reaction to form segmented poly(sulfone)-poly(arylate) co- or terpolymers. Earlier work by Lambert (281-283) showed that solution and interfacial techniques could only be utilized to synthesize segmented polymers with low poly(arylate) contents. The melt acidolysis technique allowed the synthesis of poly(sulfone)- poly(arylate) polymers with poly(arylate) contents as high as 90 weight percent.
Along with a high degree of agitation, the melt acidolysis technique utilized chlorobenzene as a solvent in the initial stage of the reaction to enhance the mixing of the poly(sulfone) oligomers and ester forming monomers, allowing true segmented polymers to be formed. This was proven by FT-IR and extraction studies, which determined that very little of the original poly(sulfone) oligomer was extracted by refluxing chloroform.
The morphology of these polymers was studied by polarized optical microscopy, and wide angle X-ray scattering. Low weight fraction poly(arylate) co- and terpolymers were determined to be amorphous, while higher poly(arylate) weight fraction polymers (15 weight percent or greater) were found to be semi-crystalline or liquid crystalline. Thermal analysis (DSC) also gave evidence that these materials were semi-crystalline or liquid crystalline. Also, as the weight fraction of poly(arylate) was increased, a significant improvement in solvent resistance was observed as well as an improvement in the modulus and tensile strength. === Ph. D. |
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