Silanes as New Highly Efficient Co-initiators for Radical Polymerization in Aerated Media

A large series of silanes are proposed as new co-initiators for radical photopolymerization. Silanes in the presence of benzophenone, isopropylthioxanthone, camphorquinone, or dyes (Eosin) are found highly reactive and, in many cases, even better than a reference amine co-initiator (ethyl dimethylaminobenzoate (EDB)). The ability of the silanes to initiate the polymerization process under air is excellent (better than with amines), and the inhibiting effect is reduced or eliminated. An enhancement of the polymerization rates R p under air is even sometimes noted. For example, using isopropylthioxanthone/tris(trimethylsilyl)silane, R p increases by a 2-fold factor when going from a laminate to an aerated medium. The hardness and the hydrophobic properties of the coatings have also been evaluated. The reaction mechanisms are discussed on the basis of laser flash photolysis experiments. Specific reaction pathways explain the unusual behavior under air.