The role of oxygen in camphorquinone-initiated photopolymerization

The activity of camphorquinone (CQ) in the photoinitiation of polymerization at various conditions (in the presence or absence of atmospheric oxygen or a coinitiator) has been studied by UV spectroscopy and differential scanning calorimetry. In the latter case the polymerization kinetics of six multifunctional (meth)acrylates of various structures was followed under isothermal conditions. In the absence of a coinitiator the rate of polymerization was found to depend on the chemical structure of the monomer and its ability to donate hydrogen to exited CQ. For most of the monomers the polymerization rate in air exceeds markedly the polymerization rate in nitrogen, which is in contrast to the situation observed for the polymerization in the presence of a coinitiator (aromatic amine). The increase in the polymerization rate in the presence of atmospheric oxygen is discussed in terms of additional formation of initiating species due to *CQ-assisted decomposition of some oxidation products arising from monomer, polymer or CQ during irradiation.