Effect of Monomer Structure on Real‐Time UV‐Curing Shrinkage Studied by a Laser Scanning Approach

Abstract

ABSTRACTThe very fast curing rate, low coating thickness (<100 µm), and a wide range of viscosity of ultraviolet (UV) systems hindered the study of UV‐curing shrinkage. A recently developed laser scanning method provided a chance to directly measure the real‐time (UV‐curing shrinkage. The effect of monomer chain lengths (degree of ethoxylation), monomer functionality, and monomer type (acrylate vs. methacrylate) on the shrinkage rates and shrinkage of UV monomers was systematically investigated. The concentration of double bonds and degree of conversion played the dominant role in the photopolymerization shrinkage and shrinkage rate. The main reason for the low shrinkage of methacrylate was that the low reactivity of methacrylate decreased the degree of conversion. The ethoxylation was an attractive way to lower the shrinkage and decrease the shrinkage rate due to significant reduction of the concentration of double bonds. The reduction of functionality was not obvious in decreasing the shrinkage or maximum shrinkage rate due to the combination effect of the concentration of double bonds and the degree of conversion. Besides, heat expansion attributed to polymerization could bring forward the maximum shrinkage rate from the shrinkage stage to the expansion stage. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 2013, 32, 21331; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21331