Polymer coatings with a wide range of properties can be made on almost any substrate by photoinitiated polymerization of multifunctional monomers. Due to its efficiency and versatility UV curing has found a large number of commercial applications in the coating, printing, and adhesives industry. The high reaction rates of photopolymerization allow high process speeds which are required for instance in printing.

Time-resolved FTIR spectroscopy is a unique method to study such fast photopolymerization reactions quantitatively and in real time. The ATR technique is the optimal configuration for irradiation of the sample and offers great flexibility in sample design. Therefore, real-time FTIR-ATR spectroscopy not only allows detailed basic investigations on the kinetics of photopolymerization, but also offers the possibility to simulate technical curing processes. Examples from both fields will be given.

RTIR-ATR spectroscopy was used for depth profiling of the degree of cure which is essential for good adhesion on the substrate or the smear-resistance of printing inks. The influence of pigmentation, UV absorbers, or the extinction of the photoinitiator was studied. Complementary investigations by confocal Raman spectroscopy were performed to determine the depth of penetration of monochromatic UV light with various wavelengths.

Temperature has a marked effect on the polymerization kinetics of viscous formulations. Whereas the ultimate conversion increases with increasing temperature, the temperature dependence of the polymerization rate was found to be influenced by the photoinitiator used. The high time resolution of RTIR spectroscopy even allows the investigation of the effect of temperature on the induction period which is in the millisecond range. Determination of the oxygen concentration in the acrylate revealed a close correlation between oxygen solubility and duration of the induction period.

The curing behaviour of various commercial systems such as printing inks, aqueous urethane acrylate dispersions for outdoor applications, or powder coatings was studied under conditions which were close to those in technical applications. Various experimental parameters were varied in order to optimize the curing process. It was proven that the results can be upscaled. Good correlation was found when RTIR data were directly compared with results obtained from curing in pilot scale performed on the printing and coating machines at IOM.