Novel Intramolecular Hydrogen Abstraction Photosensitizers (IHA-PS) for Cationic UV Curable Systems *
نویسندگان
چکیده
Novel cationic Intramolecular Hydrogen Abstraction Photosensitizers (IHA-PS) were synthesized and found to have a pronounced photosensitization effect in cycloaliphatic epoxide based cationic UV curable systems using sulfonium salt photoinitiators. A series of polyol based photosensitizers were synthesized with naphthalene attached. One polyol photosensitizer, P-Na, was found to have a much pronounced photosensitization effect in three formulation systems different in crosslink density and mobility as revealed by real time FTIR (RTIR) experiments. Such phenomenon is explained by a proposed facile Intramolecular Hydrogen Abstraction Photosensitization (IHAP) mechanism, which is possible only with the unique molecular structure of P-Na. Two non-polyol type photosensitizers were also synthesized and compared with P-Na, the result further confirmed the more pronounced photosensitization effect of P-Na. To verify the proposed mechanism and obtain a more efficient IHA-PS, a “designed” IHA-PS molecule was synthesized utilizing proposed key principles in IHAP mechanism. The “designed” IHA-PS achieved similar photosensitization effect to P-Na with only half of its molecular weight and one third of its hydroxyl groups per molecule, which further validities the proposed photosensitization mechanism.
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