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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: Structure of the phases in polydiacetylenes

Author: CAMPBELL, Alistair

Year: 1992

Supervisor(s): Craig Davies

A group of polydiacetylene derivatives with very long sidegroups are found to exhibit thermochromic properties in solution. The present work involves a study of whether the same colour changes occur in the solid state polymer crystals, and whether these changes can be linked to the distortion of the polydiacetylene backbone's electronic structure by the physical rearrangement of the molecules within the material's crystal structure.
Five different polydiacetylene derivatives are investigated in this work. These are the n-BCMU derivatives (where n = 3, 4, 6 and 9) and the 9PA derivative. The experimental techniques used are Optical and UV Absorption Spectroscopy, Differential Scanning Calorimetry, Resonant Raman Spectroscopy and X-ray Diffraction.

It is found that four distinct phases can be identified in the polymer crystals of the n-BCMU's and 9PA. These are the highly ordered blue crystalline phase, the highly ordered additional red crystalline phase, the semi-disordered red/yellow crystalline phase and the completely disordered amorphous yellow melt phase. Each phase is found to have a distinct crystal structure and a distinct polymer backbone and sidegroup conformation. The colour of each phase can be directly linked to the effect of the conformation of the polymer chain on the polydiacetylene backbone's electronic structure. The additional effects of interchain coulombic screening, intersidegroup hydrogen bonding, sidegroup structure, sidegroup conformation and polymer chain length are also investigated. The different coloured phases in the solid state crystals can be shown to be identical to those which occur in solution.