Anomalous diffusion in a model associative network with high sticker density.

The dynamic nature of the bonds in associative polymer networks has led to their use in the design of tough and self-healing hydrogels. The ability to self-heal in these networks relies on the reformation of the original network and is strongly affected by the timescale for self-diffusion. This work measured the self-diffusion of a model associative network, consisting of a linear polymer functionalized with histidine side-groups, using forced Rayleigh scattering. The effect of sticker density was investigated by synthesizing random copolymers through RAFT polymerization, with up to 15 histidine groups per chain. The polymers showed anomalous diffusion that persisted even for the highest sticker density. Earlier work has shown that anomalous diffusion as observed from FRS measurements in other associative networks, with up to four stickers per chain, primarily result from molecular hopping. These results indicate that molecular hopping could still be an important mode of self-diffusion in these networks, even at high sticker densities.