Thiol–ene chemistry of vegetable oils and their derivatives under UV and air: a model study by using infrared spectroscopy and mass spectrometry†
Herein, a model study of the photoinitiated thiol–ene reaction was carried out on unsaturated fatty methyl esters at room temperature and without photoinitiator. Reaction kinetics were monitored by FTIR spectroscopy and reaction products were identified by high resolution mass spectrometry coupled to ion mobility spectrometry. This set of analytical tools enabled us to highlight the concomitance of fatty double bond oxidation and thiol–ene addition when such a formulation was exposed to UV radiation. Indeed, thiol–ene adducts were identified on fatty moieties oxidized or not, without prevalence of one reaction over the other: photoinitiated thiol–ene addition could occur on preoxidized products, and photooxidation could occur on thiol–ene adducts. However, the presence of oxidized fatty products such as peroxides and zwitterionic species was proved to be favourable to the photocrosslinking of fatty coatings by thiol–ene addition.