Substituent effect of N-aryl-N-pyridyl ureas as thermal latent initiators on ring-opening polymerization of epoxide

A series of N-aryl-N-pyridyl ureas were synthesized by the reactions of 4-aminopyridine (4AP) with the corresponding isocyanates such as phenyl isocyanate, 4-methylphenyl isocyanate, 4-methoxyphenyl isocyanate, 4-chlorophenyl isocyanate, 4-(trifluoromethyl)phenyl isocyanate, and 4-nitrophenyl isocyanate. Bulk polymerization of diglycidyl ether of bisphenol A (DGEBA) in the presence of the ureas as initiators was evaluated by differential scanning calorimetry (DSC) at a heating rate of 10 degrees C/min. The resulting DSC profiles indicated exothermic peaks above 140 degrees C, while the DSC profile measured for a formulation composed of DGEBA and pristine 4AP indicated an exothermic peak at around 120 degrees C, implying that the derivation of 4AP into the corresponding ureas is a useful strategy to achieve thermal latency. The peak top temperatures were correlated with the electron density of the aromatic ring of the ureas, that is, as the electron-withdrawing nature of the substituent on the aromatic ring became larger, the peak increases. (c) 2015 Wiley Periodicals, Inc.