Doctoral Dissertations

Liu Da

Date of Award

8-1996

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Bernhard Wunderlich

Committee Members

Craig Barnes, Mark Dadmun, Paul Phillips

Abstract

In this work it is attempted to further the understanding of the thermotropic mesophases in macromolecules that alternate in chemical nature along the chain through quantitative studies of thermodynamic properties and molecular ordering and motion on the main-chain liquid-crystal-forming polymers: Poly (oxy-1,4-phenylene-oxyxylyleneoxy-1,4-phenyleneoxidedecamethylene) (HPX-C11) and Poly(4,4'-phthaloimido-benzoyl-dodeca-methylene-oxycarbonyl) (PEIM-12). A liquid crystal forming small molecule: N, N'-bis-(4-n-octyloxybenzal)-1,4- phenylene diamine (OOBPD) was used as a model for main-chain liquid crystalline polymers. The techniques used to study the above mentioned systems are mainly solid state 13C nuclear magnetic resonance (NMR) and thermal analysis. It is shown that in macromolecules that include mesogenic groups in the flexible chain, one can find a full spectrum of substances ranging from thermotropic and amphiphilic liquid crystals to condis crystals. Thermotropic liquid crystals achieve their special properties and structure via rod-, disk- or board-like rigid mesogens. Amphiphilic liquid crystals, in contrast, result from the formation of ordered interfaces between incompatible parts within the molecules. Condis crystals are more closely related to the crystalline state Avith translational and orientational long-range order, but with some or full conformational disorder. A series of criteria and signature properties that distinguish the liquid crystals from the condis crystals has been developed and is discussed. It is also concluded that there are cases where the distinct mesophases converge or overlap.

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