Linear Viscoelasticity of Weakly Hydrogen-Bonded Polymers near and below the Sol-Gel Transition.

Supramolecular polymers bearing weak hydrogen bonds (sticker) can express outstanding dynamic properties due to their labile association. Studying the linear viscoelasticity (LVE) of this type of polymer can provide us with sufficient knowledge to design polymeric materials for applications that need dynamic properties such as self-healing. Using different compositions of flexible weak stickers, LVE analysis showed scalings corresponding to a transition from a linear precursor to a cluster. By introducing one sticker per repeating unit of the precursor polymer, the effect of sticker distribution along the chain as well as phase separation is excluded. However, even a fully functionalized polymer could not show any network formation, whereas surprisingly, a stable cluster was formed. This proves that weakly associated networks do not dissociate rapidly and can relax as a cluster at extended time before the dissociation of stickers can lead to the relaxation of linear analogous (slow kinetics similar to strong physical or even chemical bonds.) On the other hand, the absence of a gel even in fully sticker-functionalized polymers shows that the weakness of these polymers can be described as their weakness in complete association (thermodynamically not favored).