Identifying the Influences on Network Formation in Structural Isomers of Multifunctional Epoxies

The network formation of the structural isomers of triglycidyl aminophenol cured with the structural isomers of diaminodiphenyl sulphone was monitored using three different cure monitoring techniques. Four different epoxy-rich formulations were made: TGpAP/44’DDS, TGpAP/33’DDS, TGmAP/44’DDS and TGmAP/33’DDS.
Near-infrared spectroscopy (NIR) was used to monitor the functional group concentration change throughout network formation. From this, the type of reactions occurring were identified. Differential scanning calorimetry (DSC) was used to measure the thermal response of the curing reactions, allowing for the calculation of kinetic parameters. Dielectric analysis (DEA) monitored the ion viscosity or the change in the mobility of the reactive species during the cure.
Each cure monitoring technique identified that the 33’DDS hardener was initially more reactive. During the second dwell of the cure cycle, the 44’DDS hardener formulations were found to be more reactive.
NIR identified that TGpAP formulations underwent more etherification reactions at lower temperatures as the glycidyl amine in TGpAP behaves as a more effective tertiary amine catalyst than TGmAP. TGmAP formulations consumed secondary amines earlier than the TGpAP formulations, suggesting that more internal cyclisation reactions took place in the TGmAP formulations. From this, it was found that TGpAP/44’DDS had the most homogenous network, resulting in the highest glass transition temperature and the least dense network.
DSC suggested etherification took place during network formation due to the under performance of the autocatalytic model compared to experimental data at higher degrees of cure. The multi-dwell cure was modelled using a combined isothermal and dynamic measurement technique, showing good agreement with standalone isothermal and dynamic DSC measurements.
DEA showed evidence of annealing occurring during the final parts of the cure in TGmAP/33’DDS due to its Tg falling within the cure temperature. The cure state was calculated for each technique, and good agreement was shown despite them measuring different phenomena.