(654d) Using Monomer Chemistry to Predict Dose Rate Effects during Electron Beam Polymerization

Electron-beam (EB) polymerization offers a fast, low energy, solvent and initiator free means of polymerizing inks, films, coatings, and adhesives. Because of these advantages, EB polymerization is uses to produce millions of tons of polymer product each year. However, there are some challenges to using EB polymerization. One example occurs during industrial scale-up.

EB formulations are often perfected on a pilot line before being scaled to an industrial sized beam. The dose (i.e., the energy absorbed by the sample) delivered by each EB unit is often comparable, but the speed at which the dose is delivered – dose rate – changes. Altering the dose rate can cause property changes in the final polymer, known as dose rate effects (DREs). Not all formulations experience DREs, and it is difficult to predict when they will occur. The unexpected change in final properties caused by DREs can be a costly and time-consuming problem industrially.

The research presented here establishes a relationship between DREs and monomer chemistry. DREs are minimized for monomers containing many abstractable hydrogens. Chemical modeling software was used to model hydrogen abstraction and confirmed that monomers with more abstractable hydrogens have a higher probability of generating primary radicals. Experiments were conducted to confirm the results of the model by calculating each monomer’s radiation yield (i.e., the number of radicals formed per 100 eV absorbed by the system). Monomers with low radiation yield exhibited large DREs.

Using chemical modeling to predict likelihood that a monomer will experience DREs before any experimentation takes place will expedite the scale-up process and save companies time and money. Furthermore, these predictions may help identify new formulations that can expand the use of EB polymerization into new markets. Correlating monomer chemistry, radiation yields, and DREs will help develop the structure/processing conditions/properties relationships that are currently lacking for EB polymerization.