Studies on Self-Sorting Crystalline Mixtures, Hollow Fiber Organogels and Lumen-Loaded Gels of Nonchiral Polyurethane Model Compounds

Hydrogen bond-mediated self-assembling biscarbamates were studied as model compounds of polyurethanes with respect to the crystallization and gelation behaviour in both solid state and solution phase respectively. Systematic investigation of effects of the structural features of biscarbamates on their crystallization and gelation morphologies was performed by varying the length of the alkyl side chains and the spacer group as well as the carbon atom parity and the type of terminal groups of the alkyl side chains. We found that change in any of these structural features results in significant variation in their crystallization and gelation morphology. Biscarbamate show odd-even effect in their thermal and crystallization Behaviours as a function of carbon atom parity in the alkyl side chains. Variation in the length of alkyl side chains as well as the spacer dictates the balance in relative contribution of hydrogen bonding and van der Waals force resulting in the change in their crystallization kinetics and subsequent morphology. Blending of these homologous molecules shows molecular selectivity and self-sorting behaviour leading to immiscibility. However, they mutually affect the thermal and morphological features. While the morphology can be tailored by changing any of the structural features mentioned above, blending thus provides extra control over the morphology of these molecules. Unlike monocarbamates, biscarbamates show a different morphology upon gelation. Biscarbamate gels show hollow tubular morphology because of the asymmetry of interactions between the molecules in three directions of fiber growth. We exploited the mechanism of such hollow gel fiber formation to fabricate metal nanoparticles or dye molecule-loaded organogel. The shape, size and the crystal growth kinetics of the dye molecules were found to be the governing factors in fabrication of such lumen-loaded gels. Heterologous blending of a biscarbamate with a polymer also shows immiscibility and self-sorting behaviour. We utilized such immiscibility to fabricate mechanically robust composite gels comprised of an immiscible pair of a low molecular weight organogelator and a biocompatible polymer. The gelation in this case is driven by the mutual solvophobic effect.