Connectivity defects enhance chain dynamics in supramolecular polymer model-network gels

Supramolecular polymer networks exhibit twofold dynamics: that of their polymer chains and that of the transient bonds between them, which is further complexed when irregular network structures lead to local variation of both. A typical irregularity is imperfect network-chain connectivity. To assess the impact of that, we study the diffusion of three different types of tracer polymers in supramolecular model networks of four-arm star-shaped poly(ethylene glycol). First, we focus on tracers that carry three stickers and one fluorescent label at their four arms, thereby creating an inherent network connectivity defect in their vicinity. Second, we embed tracers that carry four stickers and four labels and that do not intrinsically create network defects. Third, we embed non-sticky tracers with a larger size than the network meshes, thereby sterically obstructing their connectivity. These studies reveal that the first tracers can rapidly walk within the networks by sequential arm detachment above c*, whereas below c*, they are subject to a dynamic equilibrium of liberated and gel-cluster-bound portions. By contrast, the second tracers are efficiently incorporated into the network, which dramatically hinders their motion. Opposed to that, the third tracers can diffuse almost as unhindered as if they were embedded within an uncrosslinked matrix. (c) 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 19-29