Sulfur-containing fatty acid-based plasticizers via thiol–ene addition and oxidation: synthesis and evaluation in PVC formulations†
A new family of sulfur-containing plasticizers derived from fatty acids has been developed. The synthetic approach is based on the thiol–ene addition of alkyl thiols to the double bond of technical oleic acid, followed by oxidation of the sulfide group to either sulfoxide or sulfone groups. It has been found that both sulfide and sulfoxide derivatives are not suitable as plasticizers due to their unpleasant odor and limited thermal stabilities. However, the sulfone derivatives are odorless, thermally stable, and show plasticizing properties similar to those of established PVC plasticizers such as cyclohexane-1,2-dicarboxylic acid diisononyl ester (ELATUR® CH) and diisononyl phthalate (VESTINOL® 9). A wide range of application tests is reported to support this conclusion. Furthermore, a mixture of fatty acids obtained from commercial rapeseed oil has been used as a cheap and readily available alternative source of oleic acid to obtain such plasticizers.