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

Abstract

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).

Order–disorder transition in supramolecular polymer combs/brushes with polymeric side chains

“…Nevertheless, clusters below the gel point are formed. 25 For polymer O considering the SAXS data in Fig. 5a, one may speculate that the formation of aggregates (and a network) is more probable.…”

“…S6 †). 25 Since GPC was not possible for polymers O and T due to their interaction with the column, 1 H NMR was used for the molecular weight calculations ( Fig. 3b and S6, † Table 1).…”

“…This also makes sense considering the stronger stacking and dimerization constant of ODIN in comparison with thymine. 25,31,35,36 Therefore, the addition of side chains in the DAT system can disturb the clusters easily in comparison with the UPy system wherein strong ODIN aggregates tend to form a gel. This means in T : D4100-1 : 50 the cluster is almost completely dissociated and a comb-shaped polymer with a main chain-main chain distance of ca.…”

“…The absence of long-range ordering in the DAT and UPy systems leads to liquid-like behaviour. Although polymer T carrying THY groups has been shown to relax as a cluster, 25 after the addition of side chain polymer D the cluster dissociates and a comb-like polymer is obtained which due to tube dilation relaxes as a Newtonian liquid. 53…”

“…1,2,[4][5][6][7][8]17 Although, in these works no comparative investigation was carried out to check the effect of the sticker on the self-assembly and comb/brush formation, extensive studies were done on the simpler cases of supramolecular polymers with sticky side-groups. [18][19][20][21][22][23][24][25] The side chain in all the above-mentioned supramolecular comb/brush polymers consists of either a small amphiphilic compound with a sticker at one end or in rare cases a polymer. Mono-functionalized polymers which form the side chains have been exclusively and widely studied in the framework of supramolecular telechelic polymers.…”