Doctoral Dissertations

Date of Award

5-1992

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

B. Wunderluch

Committee Members

Paul Phillips, Craig Barnes, Alexander Van Hook

Abstract

In this work it is attempted to explore the conformational motion and disorder through a large number of examples of molecular systems differing in shape, rigidity, and molecular weight: a series of tetra-n-alkylammonium bromides and iodides, a liquid-crystal-forming molecule, N,N'-bis(4-n-octyloxybenzal)-1,4-phenylenediamine (OOBPD), and polymers, poly[oxy-1,4-(3-methylphenylene)ethylene-1,4-phenyleneoxynonamethylene] (MBPE-9) and poly[oxy-1,4-(3-methylphenylene)ethylene-1,4-phenyleneoxypentamethylene] (MPBE-5). The techniques used to study the conformational motion and disorder are mainly solid state 13C nuclear magnetic resonance (NMR) spectroscopy and thermal analysis.

The results of this work show that conformational disordered states (condis crystals) exist indeed in these molecules containing flexible chemical bonds (single bonds) or more than one accessible conformer. The unique characteristics of the condis crystal and the phase transitions to a condis crystal and to isotropic state have been studied in detail. It could be show that motifs in condis crystals show only conformational disorder but maintaining orientational and positional order, while liquid and plastic crystals show conformational motion in addition to their characteristic positional and orientational disorder and motion, respectively. The molecular motion in the condis state is slow compared to well-known plastic and liquid crystals. Besides the large-amplitude motion in a first-order transition, it is documented that gradual start of motion is possible increasing the conformational entropy over a broad temperature range.

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