Kinetic study of the cationic photopolymerization of epoxy monomers

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Abstract
The photoinitiated cationic polymerization of di‐epoxy monomers has been studied using real‐time infrared (RTIR) spectroscopy. The polymerization rate and the amount of unreacted monomer were determined directly from the conversion vs. time curves recorded. The cure speed was greatly increased by using a Kr+ laser (337.4 nm) as radiation source. A 0.25 s exposure proved sufficient to make react more than 60% of the epoxy groups. The overall polymerization quantum yield was evaluated to be 200 mol photon‐1. Dark polymerization was shown to develop extensively after the UV exposure for about 30 min and may represent up to 80% of the total process. The hardening of the UV‐cured tack‐free coating was found to occur mainly in the dark, leading after 1 h to a very hard and glassy material. A bimolecular chain termination process is postulated to account for the decay profile of the reactive species observed after UV exposure.