Material characterisationApplicability of aminophthalimide probes for monitoring and acceleration of cationic photopolymerization of epoxides

Applicability of a series of 5-substituted 3-amino-4-cyano-phthalimides as novel fluorescent probes for monitoring and acceleration of cationic photopolymerization of epoxy monomers has been studied. The performance of the following probes/accelerators were evaluated in ring opening photopolymerization of 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate (CADE) monomer: 3-amino-4-cyano-5-phenylphthalimide, 3-amino-5-(4-carboxyphenyl)-4-cyanophthalimide, 3-amino-5-(4-chlorophenyl)-4-cyanophthalimide, 3-amino-4-cyano-5-(4-methoxyphenyl)phthalimide, 3-amino-5-([1,1′]biphenyl-4-yl)-4-cyanophthalimide and 3-amino-4-cyano-5-(2-naphthyl)phthalimide. It has been found that these probes are stable under the cationic photopolymerization conditions of CADE and sensitive enough to enable monitoring the entire range of monomer conversions by Fluorescence Probe Technology, while 3-amino-4-cyano-5-(4-methoxyphenyl)phthalimide showed the best performance. At typical probe concentrations, all of the probes studied accelerated the cationic photopolymerization of CADE up to seven times compared to the compositions without any probe. Moreover, these probes shift their fluorescence spectra to longer wavelengths upon polymerization of CADE, that is in the opposite direction to most fluorescent probes. This unusual behavior of the aminophthalimide probes in CADE monomer has been explained on the basis of their solvatochromic data.