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Model compounds for liquid crystal polymers containing rod-like and disk-like mesogens

Pugh, Coleen Renee
http://rave.ohiolink.edu/etdc/view?acc_num=case1059486231

Abstract Details

1991, Doctor of Philosophy, Case Western Reserve University, Macromolecular Science.
The synthesis and thermotropic behavior of 1,2-(4,4′-dialkyloxyaryl)acetylene monomers, 1,4-bis (2-(4′,4′′-di-n-alkyloxyaryl)ethynyl) benzene dimers, and some miscellaneous 1,4-dialkyl- and 1,4-dialkyloxyphenyloxy-2-butyne monomers is described. A one pot phase transfer Pd(O)/Cu(I) catalyzed three step coupling of aryl halides with 2-methyl-3-butyn-2-ol was developed for the synthesis of the diarylacetylene derivatives. The 1,4-diaryloxy-2-butynes were prepared by etherification of 1,4-dichloro-2-butyne with two moles of a phenol. All of the 1,4-diaryloxy-2-butynes are crystalline and melt directly to the isotropic state. The effect of the n-alkyloxy chain length on the thermotropic behavior of linear 1,2-(4,4′-di-n-alkyloxyphenyl)acetylenes (n = 1-12) was examined first. All compounds with n ge 4 exhibit enantiotropic nematic mesophases, with additional crystalline and smectic mesophases. In addition to the symmetrically substituted, linear 1,2-(4,4′-di-n-alkyloxyphenyl)acetylenes, diarylacetylenes with both symmetric and asymmetric methyl branches in either the alkyloxy substituents or in the aromatic ring(s) of the mesogen were examined, as well as extension of the mesogens by one phenylethynyl unit. In general, both symmetry and methyl branching destabilize the liquid crystalline phases more than crystallinity, while extension of the mesogenic length has a stabilizing effect. Chiral methyl branched 1-(4-n-alkyloxyphenyl)-2-4′- (S(-)-2-methylbutyloxy) phenyl)acetylenes with n > 6 form cholesteric mesophases. Lateral fluorine substitution in the mesogen also destabilizes the liquid crystalline phases of 1,2-diarylacetylenes, although less so than methyl substitution. However, if the mesogen is extended by one phenylethynyl unit, destabilization of liquid crystallinity by the small fluorine substituents is compensated by the large length to bredth ratio of the mesogen. In this case, melting and crystallization are depressed more than isotropization when compared to the nonfluorinated dimers. The cyclic trimers of the 1,2-(4,4′-dialkyloxyaryl)acetylenes and the 1,4-(4,4′-dialkylphenyloxy)-2-butynes form columnar mesophases which are strongly kinetically controlled. They were prepared by either cyclotrimerization of the disubstituted acetylene or by alkylation of a disc-like molecule. Conditions were developed for selectively forming the cyclotetramer from 3,4-dialkyloxybenzyl aclohols by electrophilic cycloolgigmerization using excess CF3COOH. The resulting n-alkyloxy octasubstituted cyclotetraveratrylenes form columnar mesophases. The reaction was also used as an in situ mesogen forming polymerization reaction to form branched polymers with disc-like mesogens. The resulting oligomers also formed columnar mesophases
Virgil Percec (Advisor)
324 p.
Chemistry, Polymer
Compounds; Liquid crystal polymers; Mesogens

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Citations

  • Pugh, C. R. (1991). Model compounds for liquid crystal polymers containing rod-like and disk-like mesogens [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1059486231

    APA Style (7th edition)

  • Pugh, Coleen. Model compounds for liquid crystal polymers containing rod-like and disk-like mesogens. 1991. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1059486231.

    MLA Style (8th edition)

  • Pugh, Coleen. "Model compounds for liquid crystal polymers containing rod-like and disk-like mesogens." Doctoral dissertation, Case Western Reserve University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=case1059486231

    Chicago Manual of Style (17th edition)

case1059486231
682
© 1991, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.