Influence of monomer structure and dose rate on kinetic elements in electron-beam polymerizations

Abstract

In electron-beam (EB) polymerizations, altering the dose rate can cause property changes in the cured polymer, such as conversion, glass transition temperature (Tg), and physical or mechanical properties. These dose rate effects (DREs) complicate scale-up of EB polymerizations in industrial processes. A predictive relationship between DRE and changes in Tg was used to determine that DREs correlate to the number and lability of available bonds, not monomer size. Furthermore, the relationship between the primary radicals produced during EB irradiation and dose rate was explored via measurement of primary radical radiation chemical yield, G(R•). Namely, G(R•) is independent of dose rate, and instantaneous primary radical concentration is directly proportional to dose rate. Moreover, it was shown that non-reciprocity between dose rate and the rate of polymerization results in DREs. Future developments in radiation chemical yield measurements will aid in determining whether this disproportionality is due to the impact of dose rate on the concentration of propagating radicals or on the kinetic mechanism itself.