Simultaneous measurement of polymerization kinetics and stress development in radiation-cured coatings: A new experimental approach and relationship between the degree of conversion and stress

Stress buildup and polymerization kinetics in UV-cured multifunctional (functionality 4-8) acrylic monomers in coating fabrications have been studied simultaneously using a newly developed combined cantilever deflection method and real-time infrared spectroscopy technique. The macroscopic phenomenon in terms of stress in the film to the molecular architecture in terms of cross-link density has been correlated. Stress buildup was observed to not occur instantaneously after radiation was introduced but rather after a certain time interval. This time interval with respect to onset of polymerization is attributed to the buildup of cross-links, leading to a gel state. Furthermore, it is possible to directly associate stress development with degree of chemical reaction. These experimental observations regarding the gelation point are compared to a number of models presented in the literature. In addition, we have developed a different approach incorporating the probability of finding a relative concentration of reacted or partially reacted monomers relating the stress and degree of conversion of vinyl groups. The predicted stress-conversion relationship based on percolation models is not in good agreement with our experimental data.