Self-Sorting Sergeant-Soldier, and Majority Rules Phenomena in Crystals and Gels of Polyurethane Model Compounds

Abstract

Hydrogen bond-mediated self-assembling biscarbamates have been studied by our group as model compounds of polyurethanes with respect to the crystallization and gelation behaviour in both solid state and solution phase respectively. The aim of my thesis is to investigate the effects on the blending and the gelation of biscarbamates with different alkyl side chain lengths. Melt blending of these molecules shows molecular selectivity and self-sorting behaviour leading to immiscibility. We revealed that the difference in the growth rates of the individual species is responsible for the self-sorting behaviour in these non-chiral synthetic compounds. We discussed methods to bridge the self and non-self that would lead to a more homogeneous system. The gelation properties of biscarbamates with an odd number of carbon atoms in the alkyl side chains, such as the critical gelation concentration, gelation time, gelation temperature, and morphology of the gel fibres were examined. Biscarbamates show odd-even effects in their thermal and gelation behaviours as a function of carbon atom parity in the alkyl side chains in a similar manner to their crystallization behaviours. The blending of the biscarbamate gels shows three different types of blending behaviours. The C8/C9 blend and any gel blends composed of a biscarbamate smaller than C6 display the sergeant-soldier behaviour. The majority rules principle was observed for odd-odd gels blends with an intermediate difference in side chain length. The odd-odd gels blends with a small difference in side chain length self-sort.Organogels with a series of biscarbamates as gelators were prepared using microwave (MW) heating source as well as conventional heating. Biscarbamates with alkyl side chain lengths varying from C5 to C18 were used, with six solvents having dipole moments ranging from 0.07 to 4.3D. The minimum gelation concentration and the amount of heating for ii dissolution were significantly reduced with MW heating with benzonitrile, compared to the conventional heating for all the side chain lengths of the biscarbamates. MW heating is found to be effective with solvents possessing large dipole moments. Although the gels consist of fibers using both methods, an inherent orientation of these fibers was seen with MW heating versus conventional heating methods.iii ACKNOWLEDGEMENTS