Several ferrocenium salts as efficient photoinitiators and thermal initiators for cationic epoxy polymerization

A study of the photoinitiated and thermally initiated cationic polymerizations of epoxy oligomers with three ferrocenium salt photoinitiators bearing different arene ligands had been conducted. These photoinitiators were cyclopentadienyl-Fe-carbazole hexafluorophosphate ([Cp-Fe-carbazole]+PF6−), cyclopentadienyl-Fe-N-ethylcarbazole hexafluorophosphate ([Cp-Fe-n-ethylcarbazole]+PF6−) and cyclopentadienyl-Fe-aminonaphthalene hexafluorophosphate ([Cp-Fe-aminonaphthalene]+PF6−). They were synthesized by the reaction of ferrocene and the corresponding arenes. These ferrocenium salts were capable of photoinitiating the cationic polymerization of epoxide directly on irradiation with long-wavelength UV light. Comparative studies demonstrated that they were more effective photoinitiators than I-261 due to the strong absorption above 300 nm. Preliminary studies had shown that these photoinitiators could also be employed as thermal initiators for the cationic ring-opening polymerization of epoxides at moderate temperatures.