Solvent Induced Shape Memory Behaviour of Sulfonated Poly Ether Ether Ketone (SPEEK)

Shape memory polymers (SMPs) are a widely studied class of materials due to their numerous applications in various fields of engineering. They find applications in deployable structures, biomedical devices, adaptive optical devices, sensors and actuators, in textiles etc. Recent studies have shown shape memory behavior in many polymers. Sulfonated poly ether ether ketone (SPEEK) is an ionic polymer which is being extensively studied for its application in fuel cells as a Proton Exchange Membrane (PEM) polymer due to its relatively higher thermal and mechanical stability over other PEMs in addition to proton transport. Recent studies on a sulfonated ionomer, Nafion^® which has only one broad reversible phase transition, can show tunable, multiple shape memory effects by deforming the polymer at different temperatures without compromising the shape fixity (R_f). This paper reports, for the first time, the swelling (in solvents) induced shape memory behavior observed in SPEEK. The study was motivated by the preliminary observations of the response of SPEEK to solvent stimulus. SPEEK samples of varying degrees of sulfonation (DS) were prepared by the sulfonation of poly ether ether ketone (PEEK). The shape fixation and recovery rates (R_r) of the polymer under different temperatures and solvent conditions are reported. A comparative study of the shape memory response of the material with varying DS was also carried out. We also report for the first time the potential use of the parallel plate geometry of a rheometer for estimating the force during the shape recovery process. Visual demonstration of the shape memory effect is carried out using solvents at different temperatures.