Synthesis of dimer acid
The synthesis of the dimer acid using the fatty acid in vegetable oil followed previous reports [10,12,26,27]. The clay catalyzed method is well known as a better strategy to synthesize the dimer acids than radical coupling method, which inevitably leads to greater amounts of undesirable contents of trimers and higher oligomers [27]. In this research, the montmorillonite was used as a clay catalyst to acquire cyclic compounds. According to a previous study, dimer acids could be synthesized up to 89.6% conversion yield (mass of synthesized dimer acids/mass of unsaturated fatty acids in vegetable oil) using an acidic clay catalyst at 250 ๐C for 4 h reaction [10].