On novel cross-linked formulations made from epoxidized soybean oil acrylate and N-isopropylacrylamide

This work deals with the development of novel formulations based on compounds from renewable sources, an area of great interest as it addresses the need to limit the use of materials from fossil sources. Among the various bio-based systems, those derived from soy, such as soybean oil or modified soybean oil, are particularly promising. In particular, the present study was conducted with the aim of extending the applicability of epoxidized soybean oil acrylate (ESOA). To this end, the development of formulations based on ESOA with peculiar functional and structural properties, was investigated. In this contest, ESOA was combined with a polymer of great interest, namely poly(N-isopropylacrylamide) (PNIPAAm), via a reactive radical process, to develop innovative materials with modified properties compared to those obtained from NIPAAm and ESOA. Formulations with different ESOA/NIPAAm ratios were prepared using trihexyl tetradecyl phosphonium persulphate (TETDPPS), a radical initiator capable of generating radical species without gas evolution. Furthermore, frontal polymerization, a fast and energy efficient preparation technique , was used and the process was studied by evaluating the front velocity (Vf) and front temperature (Tmax). The analysis of these parameters revealed a significant correlation with the component ratio, with both Tmax and Vf increasing with NIPAAm content, and frontal polymerization being feasible up to an ESOA/NIPAAm ratio of 90. Morphological analysis performed with Field Emission Scanning Electron Microscope (FE-SEM), showed a decrease in porosity with increasing ESOA content, while thermal analysis displayed a single glass transition temperature for all the samples, thus demonstrating a good compatibility between the components, and the role of ESOA as a comonomer and crosslinker. Moreover, Dynamic Mechanical Analysis (DMA) demonstrated a significant increase in elastic modulus with increasing ESOA concentration in the formulations. Finally, a formulation characterized by the right combination of swelling and hydrophobicity was found, allowing to maximize the adsorption capacity of hydrophobic compounds – a property not present in normal PNIPAAm-based systems. The properties of the developed materials, the renewable source for one of the two components as well as the applied polymerization method make the systems promising in terms of their application and large-scale development.