Effect of intermolecular interactions on the glass transition temperature of chemically modified alternating polyketones

Thermal properties of polymers depend on the chemical structure of the polymer chain and intermolecular forces arising from hydrogen bonding and π-π stacking. Here we analyzed the effect of increasing the amount of supramolecular interactions on the glass transition temperature of polyketones by chemically modifying the same polymer backbone with five amine derivatives, namely (1-(3-aminopropyl)-imidazole, 4-(aminomethyl) benzoic acid, 6-aminohexanoic acid, benzylamine or hexylamine, at various molar concentrations. The grafting was performed via the Paal-Knorr reaction and the interactions between the pyrrole backbone and different grafted functional groups were elucidated by proton nuclear magnetic resonance, Fourier transform infrared and X-ray photoelectron spectroscopy as well as differential scanning calorimetry and computational modeling. The modification of polyketone with 4-(aminomethyl) benzoic acid and 6-aminohexanoic acid, allowed for new possibilities of hydrogen bonding and led to a significant increase in the glass transition temperature as compared to the neat polymer and pyrrole-containing polymers that did not bear reactive side groups. In contrast, modification with the imidazole derivative was found to introduce new and more robust CH⋯π interactions between imidazole groups and the π-system of the pyrrole backbone chain, based on electrostatic effects. Both types of supramolecular interactions affect the mobility of the backbone chains and this systematic study demonstrates how the combined effect of π-π stacking and hydrogen bonding to carboxylate moieties can be used to tune the molecular mobility and phase transition temperature of these chemically modified polyketones.