Polymethylferrocene-induced photopolymerization of cyanoacrylates using visible and near-infrared light

Metallocene-induced photopolymerization of cyanoacrylates based on electron transfer processes has been proposed as an alternative to more conventional light-curing strategies relying on photobase generators. However, successful application of this methodology has so far only been achieved for very reactive cyanoacrylates under UV illumination and long irradiation times, which eventually hampers its practical use. To overcome these limitations, we describe in this work the use of electron-rich polymethylferrocenes as photoinitiators, with which fast light-induced polymerization of commercial formulations of less reactive, but more relevant long alkyl chain cyanoacrylates has been accomplished by illumination with visible and even near-infrared light. In addition, generalization of this technology to other electron-deficient, noncyanoacrylate monomers has been demonstrated. The low oxidation potential of polymethylferrocenes accounts for these excellent results, which strongly favors the formation of radical anions by electron transfer that initiate the polymerization reaction. Because of the high molecular weight and superior adhesive behavior of the resulting polymer materials as well as the facile access to polymethylferrocenes, they emerge as very attractive photoinitiators for the light-curing of cyanoacrylate (and other) glues in real applications.