Shape memory polymer networks based on methacrylated fatty acids

Abstract

In this study, bio-based materials were prepared from fatty acid precursors and variable amounts of styrene or divinylbenzene by free-radical polymerization. The obtained materials were highly translucent and resulted insoluble in common organic and aqueous solvents. They exhibit a complex microstructure due to the formation of highly cross-linked arrangements (micro/nanogels) closed packed into clusters. The bio-polymers prepared with divinylbenzene (a tetra-functional monomer), due to their excessive cross-linkage, resulted in brittle samples whose mechanical response could not be obtained. On the other hand, bio-based polymers obtained from styrene (a bi-functional monomer) resulted in materials with a moderate cross-linking density, a sharp glass-rubber transition and acceptable mechanical properties, leading to polymers with interesting shape memory response (switching temperature, fixity and recovery ratios) that could be tailored by changing the composition. In these materials it was corroborated that higher (but not excessive) cross-linking density led to a greater shape recovery, since cross-links are the responsible for memorizing the original shape of the material.