On a promising and effective combination of epoxidized soybean oil acrylate with N-isopropylacrylamide in the development of cross-linked materials

With the aim of expanding the application possibilities of a derivative of soybean oil, namely epoxidized soybean oil acrylate (ESOA), a compound from renewable sources, by giving it functional and structural properties, the development of its formulations was investigated in this work. ESOA was combined with N-isopropylacrylamide (NIPAAm) by a reactive radical process to modify not only the features of the oil but also those of poly(N-isopropylacrylamide) (PNIPAAm), in particular to improve its mechanical properties and its retention capacity for hydrophobic molecules. The formulations, based on different ratios of ESOA/NIPAAm, were prepared using trihexyl tetradecyl phosphonium persulfate (TETDPPS) as a non-gas-releasing radical initiator, and applying a very energy-efficient polymerization method, i.e., frontal polymerization. The investigation of the polymerization front velocity (Vf) and the front temperature (Tmax) showed a significant dependence of these two parameters on the ratio of the two components, with an increase in Tmax and Vf with the amount of NIPAAm and with a limit of front formation up to an ESOA/NIPAAm ratio of 90. As indicated by the microscopic measurements, the prepared formulations showed a decreasing porosity with increasing ESOA amount, while the DSC analyses proved a good compatibility between the components, which was favored by the formation of a copolymeric system during the free radical polymerization process. The mechanical properties were investigated by DMA compression analyses, which revealed a relevant increase in modulus when increasing the ESOA content in the reaction mixture. It was also found that the swelling and the ability to retain hydrophobic compounds depends on the initial composition, with the former parameter decreasing with increasing the ESOA/NIPAAm ratio and the retention capacity increasing significantly with increasing ESOA content in the reaction mixture.