Experimental and theoretical investigations of free radical photopolymerization: Inhibition and termination reactions

Abstract

In this work, the inhibition and termination reactions occurring throughout a free radical photopolymerization initiated by a type-I photoinitiator are studied by kinetic modeling. The role of the macroradicals as the main oxygen trapping agents during the inhibition time is identified, and the absence of primary radical consumption by oxygen can be related to a high initiation efficiency at early times. The ratio of the termination reactions reveals that bimolecular termination remains the principal pathway for the cessation of macromolecule growth, even at high polymer conversion. Moreover, the evolution of the termination ratio during the polymerization can be correlated to both the diffusional control of the polymerization reactions as the polymer network grows and the photoinitiator consumption. Finally, the effect of the incident light intensity and the initial photoinitiator concentration on the termination reactions is assessed, and the validity of the steady-state assumption applied to the macroradical concentration discussed.

Photochemical Study of a Three‐Component Photocyclic Initiating System for Free Radical Photopolymerization: Implementing a Model for Digital Light Processing 3D Printing

“…In this study, β=0.61 (Figure S1), indicating a mostly bimolecular recombination termination at Rp max , in agreement with other works . However, during the process of photopolymerization, many phenomena affect the termination mechanisms and β actually varies.…”

Yellow Triazine as an Efficient Photoinitiator for Polymerization and 3D Printing under LEDs

“…The excessive PIs at the surface will also hinder the transmission of light into deeper layer and reduce the polymerization therein . Therefore, significant termination would occur when PIs are overdosed due to the biradical coupling, resulting in limited increase in Cs . The polymerization profiles of TetEGDA containing between 0.01 and 0.5 wt% R‐Cl under LED@400 nm are recorded in Figure and Figure S6, Supporting Information.…”

Effect of Light Intensity on the Free-Radical Photopolymerization Kinetics of 2-Hydroxyethyl Methacrylate: Experiments and Simulations

“…( 8)). At the end of the process, remaining nonreacted macroradicals n P  are trapped by occlusion in the polymer network underwent vitrification 17 This assumption was confirmed by modelling showed that the concentration of [] Bn RP is three orders of magnitude higher than that of [] An RP (figure S3 of ESI). Therefore, the very low proportion of An RPspecies is not represented in figure 6.…”

“…More precisely, the effectiveness of PRT process depends on two factors: (i) consumption of photoinitiator molecules and (ii) competition between PRT and initiation reactions. This last factor can be expressed by a ratio between PRT and initiation rates 17 : 7) and these radicals are not involved in the PRT process.…”

“…However, most of these models do not take into account the competition between different termination processes, considering only bimolecular processes between macroradicals. Studies analyzing details of the termination modes during FRP process are rare [17][18] . From experimental point of view, common ways for monitoring the FRP kinetics are based on differential scanning calorimetry (DSC) or dilatometry, which are indirect approaches and offer response times of typically 1 second.…”