Synthesis and characterization of supramolecular polymer based on linoleic acid of sunflower oil

Abstract

This research was intended to produce and characterize the supramolecular polymer based on linoleic acid of sunflower oil. The synthesis involved a three steps reaction. The first step was the preparation of dimer acid from linoleic acid of sunflower oil by using Diels-Alder reaction. The second step was preparation of oligoamides by condensation process of dimer acid and diethylenetriamine. The third step was the reaction of the oligoamides with urea to produce supramolecular polymers. The structure of supramolecular polymer as analyzed by Fourier Transform Infrared (FTIR) spectroscopy and Nuclear Magnetic Resonance (NMR) techniques reveals not only the main triglycerides but also primary and secondary amine functional groups which may present as free amine and amine bonded through hydrogen bond. FTIR analysis showed that free amine functional groups appear at 3426 cm-1 and 3348 cm-1 representing N-H stretching of primary and secondary amines as well as at 1614 cm-1 and 1603 cm-1 representing N-H deformation of primary and secondary amines, respectively. The presence of amine bonded hydrogen bonds in the supramolecular polymer is indicated by peaks at 780 cm-1 and 706 cm-1 owing to out-of-plane N-H deformation of primary and secondary amines. NMR analysis also show the appearance amine functional groups at peak 5.4 ppm in 1H NMR representing proton in amine functional group and peaks at 151 ppm and 156.6 ppm in 13C NMR representing carbon in amine functional groups. Moreover, the presence of hydrogen bonding is indicated by infrared peaks in the region 2300 cm-1 to 3700 cm-1 representing hydrogen bonded hydroxyl group from primary and secondary amines. The existence of hydrogen bonding in supramolecular polymer is also detected by the appearance of an endothermic peak in the region of 116 – 131 oC as indicated by Differential Scanning Calorimetry (DSC). This peak has broad and low intensity indicating limited numbers of supramolecular polymer formed via hydrogen bondings. All results confirmed that sunflower oil-based supramolecular polymer was formed from oligoamides connected via hydrogen bond.