Hybrid free-radical and cationic photo-polymerization of bio-based monomers derived from seed oils – control of competitive processes by experimental design

Abstract : Hybrid photopolymerization processing by concomitant cationic and free radical mechanisms was investigated from a basic viewpoint for elaborating polymer networks from mixtures of multifunctional epoxy and acrylate monomers derived from seed oils, namely epoxy linseed oil (ELO) and acrylated epoxidized soybean oil (AESO). The influence of monomer composition and processing parameters controlling the properties of UV-cured films was studied by experimental design (ED) methodology. UV-curable formulations including ELO and AESO were prepared with different concentrations of a photo-initiator system including a diaryliodonium salt, a thioxanthone photosensitizer and isopropanol as a H-donor. A deconvolution method was applied to FTIR spectra for quantifying separately the progress of acrylate and epoxy polymerization at 1406 and 830 cm−1, respectively. The efficiency of the photo-initiator system was studied by means of Scheffé's mixture design. The obtained data reveal that the polymerization rates of the two monomers are strongly influenced by the ratio of isopropyl thioxanthone with respect to the iodonium salt. The predicting model was used for preparing hybrid networks with different microstructures and specific thermomechanical properties.