Recyclable shape-memory polymer: Poly(lactic acid) crosslinked by a thermoreversible Diels-Alder reaction

An intelligent shape-memory polymer was made through the synthesis of poly(lactic acid) macromonomers with furanyl groups and crosslinking with linkers with maleimidyl groups. The thermoreversible covalent bonds formed by the Diels-Alder reaction between these groups made this polymer recyclable (i.e., environmentally friendly). The structure of the polymer was also studied. A defect of the structure, a dissociated moiety of the thermoreversible bonding, was strongly affected by the reaction conditions and was investigated with UV spectroscopy, which was used to monitor the concentration of the maleimidyl groups. The relation between the flexibility of the linker and the strength and inner stress of the polymer was also evaluated. Reducing the number of defects and relaxing the inner stress were found to increase the strength of the shape-memory polymer.