Temperature-dependent FTIR spectroscopic and thermoanalytic studies of hydrogen bonding of hydroxyl (phenolic group) terminated hyperbranched aromatic polyesters

The formation and modification of inter- and intramolecular hydrogen bonds of hydroxyl (phenolic group) terminated hyperbranched aromatic polyesters (HBP-OH) have been studied by temperature-dependent Fourier transform infrared (FTIR) spectroscopy. Three ‘heating–annealing–cooling’ (HAC) cycles starting from room temperature to 235 °C were measured. The IR spectroscopic results indicate different types of hydrogen bond association. The weakening and breaking of hydrogen bonds with increasing temperature was observed. Additionally, a curve fitting procedure of the hydroxyl and carbonyl vibration regions has been done to gather additional information of the hydrogen bond association. On the basis of the band shifts and the changes of the normalised integral band intensity (NIBI) and halfwidth of a band (HWB), the formation of a network of hydrogen bonds was proposed. Four different interactions regarding hydroxyl (phenolic) groups association were detected. Several types of associated carbonyl groups existing within HBP-OH were revealed. The spectra and curve fitting results indicate the relative stability of formed bond structures with participation of the ester groups of the HBP rigid segments in the studied temperature region. Differential scanning calorimetry (DSC) was applied to reveal changes in thermal behaviour after the first, the second and the third HAC cycle. As expected, the aromatic ester backbone structure strongly influences the glass transition. Therefore, the performed measurements did not show any changes in glass transition related to the rearrangements in the hydrogen bonded network.