Using Monomer Chemistry to Predict If Dose Rate Effects Will Occur during EB-Polymerization

Through radiation polymerization the formation of polymer is initiated by exposing a batch of monomer to an initiation energy, like gamma radiation, light or charged particles, that drives the initiation and propagation of large chains composed of repeating monomer units. Electron-beam-irradiation (EB) has been shown as a promising method for radiation initiation of monomers that can be controlled by altering the samples operation voltage and belt speed, changing the processes dose rate. Dose rate effects (DREs) are variations in polymer properties (e.g., conversion, glass transition temperature, molecular weight, etc.) due to changes in the samples dose rate which can hinder EB polymerization growth in industrial settings. Because the dosage of a sample often changes during scaling this has led to unpredictable or varying properties DREs do not occur in all formulation chemistries or under all processing conditions, which makes predicting their occurrence challenging. This lack of understanding is especially problematic when predicting final polymer properties during industrial scale-up from a pilot line. Building off from previous work from affiliated graduates there are many factors still unexplored in predicting factors that cause dose rate effects and being able to predict those effects for materials at different operating conditions. This project explored and tested effects caused by monomer chemistry and compared DREs experienced by comparable monomers. Dynamic mechanical analysis was used to determine and compare the glass transition temperature of several acrylate monomers polymerized at different dose rates. Monomer chemistry was carefully chosen to determine the impact of size and number of abstractable hydrogens on the magnitude of the DREs. Results show that increasing the number of abstractable hydrogen plays a key role in reducing DREs. Results from this study will allow scientists to more easily identify formulation chemistries less prone to DREs, making industrial scale-up for electron beam polymerization more predictable and reliable.