In this talk, we will discuss the ordering and clustering of dynamic bonds in dynamic polymer networks under strain. In contrast to affine deformation, in which junction points in the network are assumed to deform uniformly, we show that the directional nature of many dynamic bonds can result in the formation of highly anisotropic strain-induced supramolecular structures from isotropic amorphous polymer films. These structures enable exceptionally high energy density shape memory polymers with large recovery stress, due to the stabilization of highly stretched chains by the formation of ordered dynamic bonding domains. The high extent of structure formation is clear from an increase in small-angle x-ray scattering intensity by over two orders of magnitude, from AFM images of the strained sample showing the emergence of ordered, periodic nanofibers, and from macroscopic stress whitening of the bulk films indicating the emergence of large domains. We synthesize alternative molecular polymer architectures to better understand the origin of this strain-induced ordering and extend our design to achieve more complex shape actuation. This works shows that initially amorphous networks of dynamic covalent or supramolecular polymers can be molecularly-programmed to undergo assembly under strain and that this assembly can dramatically alter material properties.

Characterizing the formation of strain-induced supramolecular structures in dynamic polymer networks

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