How diffusion of small molecules into shape memory polymers can trigger the one-way effect

During programming, shape memory polymers are strongly deformed. This deformation is stored and can later be recovered [1]. It is well known that an increase of temperature triggers the one-way effect. It is less well appreciated that the one-way effect can also be chemically triggered [2]. In the present study [3] we demonstrate this second phenomenon by first investigating the diffusion of the small molecules acetone, ethanol and water into a shape memory polyurethane (Lubrizol Estane ETE 75 DT3, abbreviation: SMP-E), using a weight gain method and subsequent numerical analysis of the diffusion data (diffusion coefficients: D_acetone>D_ethanol>D_water). Figure 1 shows an Arrhenius plot of the temperature dependence of the three diffusion coefficients determined in the present work [3].

Figure 1: Arrhenius plot of diffusion coefficients in the polyurethane SMP-E. The apparent activation energies for diffusion are given in the figure.

We then show how the diffusion of small molecules into the shape memory polymer triggers the one- way effect. We use an in-situ method to precisely monitor the recovery kinetics as the programmed shape memory polymer returns towards its original shape, Figure 2. The study represents a contribution to the field of diffusion-controlled chemical/mechanical coupling phenomena.

Figure 2: Return of programmed shape memory polymer towards its original shape.

1. Behl, M.; Lendlein, A. Shape-memory polymers. Materials Today 2007, 10, 20–28.
2. Yang, B.; Huang, W. M.; Li, C.; Lee, C. M.; Li, L. On the effects of moisture in a polyurethane shape memory polymer. Smart Mater. Struct. 2004, 13, 191–195.
3. Marquardt, A.; Mogharebi, S.; Neuking, K.; Varnik, F.; Eggeler, G. Diffusion of small molecules in a shape memory polymer. J. Mater. Sci. 2016, 51, 9792–9804.