Inhibition of premature polymerization of cationically polymerizable low viscosity systems

Photocurable inkjet inks based on cationically curable materials are a promising new technology with many advantages and some problems yet to be solved. One of the latter is the long-term stability of liquid inks. Reactive monomers are stable in the dark at room temperature for a long time. When a photoinitiator (iodonium salt) is added, premature gelation takes place within several days, depending on the temperature. Tertiary amine, hindered amine, hindered phenol, a quinone derivative, a sulphur-based antioxidant, beta-carotene and their selected mixtures were tested as potential inhibitors of premature cationic polymerization by being subjected to accelerated ageing at higher temperatures. The influence of additives on photoinitiated polymerization was studied by means of FTIR spectroscopy. The inhibition effect of additives was ascertained by monitoring the changes in viscosity during long-term temperature exposition as well. The system used for the study was a model system containing a cycloaliphatic epoxide monomer, oxetane monomers and a diaryliodonium salt photoinitiator. Amines, in contrast to antioxidants, proved to be effective as premature polymerization inhibitors.

► The inhibition effect on premature cationic polymerization of the selected additives was tested in low viscosity model system.
► Amines are effective inhibitors.
► Primary antioxidants scavenging free radicals are not effective inhibitors.
► In contrast, their combination with triethanolamine exhibited a strong adverse effect on photoinitiated polymerization.
► Neither the secondary antioxidant nor the singlet oxygen scavenger (beta-carotene) exhibited any inhibition effect.