Non-extractable photoinitiators based on thiol-functionalized benzophenones and thioxanthones |
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Authors: | Hironori Matsushima Qin Li Masamitsu Shirai Charles E Hoyle |
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Institution: | a School of Polymer Sciences and High Performance Materials, The University of Southern Mississippi, Hattiesburg, MS 39406, USA b Department of Applied Chemistry, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan |
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Abstract: | Non-extractable photoinitiators could be advantageous for use in biological, electronic, and food packaging applications. Therefore, thioxanthone and benzophenone derivatives were synthesized from 1,6-hexane dithiol and chlorinated benzophenone or thioxanthone. The efficiency of thiol-functionalized photoinitiators in combination with amine co-initiators was compared to benzophenone and isopropylthioxanthone with amine co-initiators, and the cleavage of photoinitiator 2,2-dimethoxy-1,2-diphenylethan-1-one in acrylic resins. The reaction kinetics were analyzed using photo-differential scanning calorimetry and real-time FTIR. Coating physical properties were evaluated by pendulum and pencil hardness, steel-wool scratch and mandrel bend tests. The non-extractable photoinitiators had higher absorbance than their benzophenone or isopropylthioxanthone counterparts due to the sulfide substitution on the phenyl ring, and the free thiol groups reacted with the acrylate by either an amine catalyzed Michael addition or a free-radical chain process. The combination of thiol-functionalized photoinitiators with secondary amines provides an efficient photoinitiator system that is locked into the photopolymerized network and cannot be extracted with typical solvents. |
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Keywords: | Photoinitiator Thioxanthone Benzophenone UV curing Non-extractable |
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