Modeling the Dual-Function Effects of Free Radical and Cationic Hybrid-Photopolymerization in Iodonium/Amine System

The synergistic features of a three-component, photoinitiating system (A/B/C) based on the measured data and proposed mechanism of Liu et al. are analyzed. The co-initiators/additives B and C have dual-functions of : (i) regeneration of photoinitiator A, and (ii) generation of extra radicals for enhanced conversion efficacy (CE). The synergistic effects led to higher CE for both free radical polymerization (FRP) and cationic polymerization (CP). The CE of FRP has 3 terms due to the direct (tyep-I) coupling of the triplet state of A with the monomer (M) and the coupling of the two radicals, R and R', with M. The CE of CP has a transient state proportional to the effective absorption constant (b), the light intensity (I) and initiator concentration (A0), but a steady state is independent of the light intensity (I). For the CE of FRP, the contribution from radical R had two cases: (i) linear dependence on T=bIA0, or (ii) nonlinear square root dependence T0.5. The synergistic effects led to higher conversion of FRP and CP, consistent with the measured results. The theoretically predicted new features include: (i) co-initiator [C] which always enhances both FRP and CP conversions, and (ii) co-initiator [B] which leads to more efficient FRP, but it also reduces CP.