Nonequilibrium Transesterification for Programming a Material's Stiffening

On-demand stiffening is ubiquitous in nature but not in artificial materials. Herein, we describe a self-stiffening approach that features fast stiffening rate, huge stiffening range, and excellent spatial control. The strategy is based on the continuous removal of the small transesterification products to drive the equilibrium toward the esterification state. The initial elastomers can evolve from a rubber to a plastic with a change of three orders of magnitude in modulus. Moreover, the process is also spatially control-lable. These appealing features allow programming of mechanical heterogeneities and gradients as well as the shape of materials via site-specifically seeding the transesterification catalyst.