Quantitative comparison of photo- and electron-beam polymerizations based on equivalent initiation energy

Abstract

Electron-beam (EB) and photopolymerization rely on radiation chemistry; however, fundamental differences arise in initiation and energy deposition. Since photopolymerization has been widely studied, a quantitative comparison would facilitate a better understanding of the kinetic and physical impact of the EB initiation mechanism, which is substantially more difficult to characterize. Here, a protocol was developed that enables investigation of EB and photopolymerized films of equivalent initiation energies. Using this protocol, the impact of the initiation mechanism on energy rate effects (EREs) was characterized for a series of five acrylate monomers. Differences in polymer conversion and physical properties were determined via Raman spectroscopy and dynamic mechanical analysis, respectively. In comparison to the EB-polymerized films of equivalent initiation energy and energy rate, the photopolymerized films had equal or lower conversions. Additionally, monomer chemistry was a key factor for differentiating ERE magnitude across the five-monomer series for both initiation mechanisms. Differences between initiation mechanisms were also demonstrated in Tg, FWHM of the tan δ peak, and the maximum tan δ peak height for two of the monomer formulations. Quantifying these differences not only improves knowledge of fundamental kinetics, but also provides a foundation for predictive chemical structure/processing parameter/polymer property relationships.