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

Abstract

The 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. C 2012 Wiley Periodicals, Inc. Adv Polym Techn 2013, 32, 21331; View this article online at wileyonlinelibrary.com.

Free Radical Photopolymerization of Multifunctional Monomers

“…For di(meth)acrylate monomers the increase in the length of the spacer between two unsaturations led to higher final conversions because decrease in cross-link density enhances mobility of the system [78,79]. Similarly, for triacrylate monomers, for example, trimethylolpropane triacrylate (TMPTA) and ethoxylated TMPTA, final conversions increase with the degree of ethoxylation, for example, from about 45% for TMPTA to about 90% in the case of TMPTA containing 15 ethoxy groups [81] due to formation of less dense network. Similarly, for triacrylate monomers, for example, trimethylolpropane triacrylate (TMPTA) and ethoxylated TMPTA, final conversions increase with the degree of ethoxylation, for example, from about 45% for TMPTA to about 90% in the case of TMPTA containing 15 ethoxy groups [81] due to formation of less dense network.…”

Photopolymerization Kinetics of Block Polyether Based Terminal Urethane Methacrylate with/without Cross‐Linker

“…Generally, for ultrafast polymerization reactions, higher final degrees of conversion can be attained in cases where the volume shrinkage occurs over a much longer timescale than the chemical conversion . However, quantification of volume shrinkage using photo DSC is difficult, due to lesser amount of sample used for analysis . For the system containing the cross‐linker, the ultimate conversion on calculation was observed to be over 100%.…”

“…23 However, quantification of volume shrinkage using photo DSC is difficult, due to lesser amount of sample used for analysis. 24 For the system containing the crosslinker, the ultimate conversion on calculation was observed to be over 100%. Ward et al have observed that during the photocopolymerization of polyethylene glycol-based methacrylate and dimethacrylate, the ultimate conversion in certain cases has been calculated to be above 100%.…”

Design of Highly Adhesive and Water-Resistant UV/Heat Dual-Curable Epoxy–Acrylate Composite for Narrow Bezel Display Based on Reactive Organic–Inorganic Hybrid Nanoparticles

“…It is supposed that the enhanced resin compatibility and high curing ratio of the proposed composites induce densely photocrosslinked network between reactive hybrid nanoparticles and matrix resins, leading to the improvement in the adhesion strength. Moreover, the methacrylate groups in the surface of nanoparticles offer high adhesive strength and low shrinkage compared to the acrylate groups [ 35 , 36 ]. Notably, the epoxy–acrylate composite including reactive aluminum oxide nanoparticles exhibited a relatively high adhesion strength due to the high UV and heat curing ratios compared to that of the composite with reactive silica nanoparticles.…”