Inhibiting the Self-Sorting Behavior in the Blends of a Homologous Set of Polyurethane Model Compounds

Organogelating and narcissistic self-sorting behaviour of non-preorganized oligoamides

Depending on the length (n) and the nature of the end group (X), structurally flexible oligoamides OAT and OATe were found to be good organogelators and their mixtures showed narcissistic self-sorting in both the xerogel and wet gel states.

Several series of structurally flexible, non-preorganized oligoamides with carboxylic acid, hydride, N-propargyl amide and N-propyl amide end groups were synthesized and characterized. They were found to be strong organogelators for aromatic solvents. Both the number and density of the amide units, and the nature of the end group were found to influence the gel strength as well as the kinetics of gel formation. Oligomers with a higher number and density of amide units were found to form stronger gels. Rather unexpectedly, a slight change of the end group could significantly affect the enthalpy and entropy of formation of the resulting self-assembly. Oligomers with the N-propargyl amide end group were found to be kinetically trapped in the melted state, which devoid them of forming crystalline zone upon cooling. On the other hand, the corresponding saturated N-propyl amide analog did not show the same effect. Upon mixing of these oligomers, narcissistic self-sorting could be observed in both the wet gel and xerogel states if (i) the difference in the number of amide units is greater than one or (ii) the amide unit densities are different. A semi-quantitative assessment of the extent of self-sorting could be achieved by constructing the corresponding phase diagram of the mixed gel systems. It is concluded that narcissistic self-sorting does not just prevail in mixtures making up of structurally different molecules, but appears to be fairly general even in mixtures of structurally similar molecular homologs.

Effect of Reinforcement at Length Scale for Polyurethane Cellular Scaffolds by Supramolecular Assemblies

This study is aimed to represent the role of carbonaceous nanofillers to reinforce the commercially available polyurethane porous structure. The effect of dimensionality of fillers to anchor the construction of stable three-dimensional (3D) cellular architectures has been highlighted. The cellular frameworks of commercially available thermoplastic polyurethane (TPU) have been fabricated through the thermoreversible supramolecular self-assembly route. It was established that the minimum shrinkage of TPU lattice structures occurred when the solid-state network is strengthened by the topologically engineered 3D hierarchical nanofillers, where the amount of reinforcement was found to play a critical role. It has been established by series of structure-property correlations that reinforcing the cellular structure to endure the capillary stress is equally effective as supercritical drying for producing low-density porous morphologies. The removal of liquid phase from gel is as important as the presence of 3D fillers in the matrix for reinforcing the cellular structures when replacing the solvent phase with air to generate a two-phase solid-gas engineered morphology. The insight into the polyurethane network structure revealed that the dimensionality, amount, and distribution of fillers in the matrix are critical for reinforcing the cellular scaffolds in solid gel without any cross-linking.