Decreased oxygen inhibition in photopolymerized acrylate/epoxide hybrid polymer coatings as demonstrated by Raman spectroscopy

Photopolymerization systems based on hybrid monomer 3,4-epoxy-cyclohexylmethyl methacrylate (METHB) were studied to investigate the oxygen inhibition effects on the conversion and polymer properties in films and coatings. METHB contains epoxide and methacrylate functional groups, which undergo cationic and free-radical photopolymerization, respectively. The conversion of both groups was obtained by Raman confocal microscopy as a function of depth. Initiator system compositions were varied and shown to affect the depth profile. The methacrylate group conversion was low at the surface due to oxygen inhibition. When both reactions were present, a cross-linked network formed and reduced oxygen sensitivity. At depths greater than the oxygen-diffusion-affected region, both functional groups' conversions did not show depth dependence. In addition, epoxide groups continued reacting after light was shuttered and reached a higher and more homogeneous conversion. These systems exhibit lower sensitivity to oxygen and offer advantages such as increased cure speed and improved film-forming properties compared to free-radical systems.