Figure 3 (a) Schematic representation of poly[2]catenane networks upon addition of DMSO, (b) 1H NMR spectra (400 MHz, CDCl3, 298 K) of (I) poly[2]catenane networks and (II) the addition of 10% DMSO-d6 (v :v ) into poly[2]catenane networks (poly[2]catenane networks were prepared by adding 5 mmol M3 and 90 mmol M2 into 50 mmol M1 ), (c) photographs ofG1 and G1’ (after adding DMSO to G1 ), whereG1 was prepared by adding 10 mmol M3 and 180 mmolM2 to 100 mmol M1 , (d) storage modulus (G’ ) and loss modulus (G’ ’ ) with versus scanning frequency (ω ) for the G1 and G1’ .
Since the formation of the poly[2]catenane networks was driven by hydrogen bonding interactions, the solvent response of poly[2]catenane after the addition of DMSO was investigated. As shown in Figure 3a, hydrogen bonding interactions originated from the amide hydrogen in polycatenanes caused the catenanes to be immobilized, whereas the hydrogen bonding was disrupted upon the addition of DMSO. But this would not affect the structure of poly[2]catenane structure. To verify this, the mixture of M1 , M2 andM3 was first obtained by adding 5 mmol M3 and 90 mmolM2 into 50 mmol M1 in chloroform, and then 10% DMSO-d6 was added to the mixture. Besides, the corresponding 1H NMR spectra of the mixture before and after adding DMSO were performed (Figure 3b, S10). With the addition of DMSO-d6 , it could be found from the spectra that the signal of amide hydrogen Ha shifted from 7.88 ppm to 8.74 ppm, which indicated that the intramolecular hydrogen bonding was partially disrupted on account of the newly formed hydrogen bonding from the amide hydrogen. The signal peak of the imide hydrogen (Hb) remained almost unchanged, indicating that the poly[2]catenane structure was not disrupted.[28] Next, gel G1 was obtained by adding 10 mmol M3 and 180 mmol M2 to the SPs formed from 100 mmol M1 in chloroform, and then gel G1’ was obtained by adding DMSO to G1 (Figure 3c). As can be seen from the photographs, there was no significant change in the state of the gel before and after the addition of DMSO, which indicated that although the hydrogen bonding was destroyed. But the gel network was not dissolved owing to the existence of poly[2]catenane structure. Meanwhile, the rheological experiments were carried out on the gels G1 ,G1’ (Figure 3d). The results showed that the storage modulus ofG1 and G1’ was greater than the loss modulus in a certain frequency range (0.6 to 100 rad/s at a strain of 1%). This indicated that the gel state did not change due to the existence of dynamic covalent bonds. The storage modulus of G1’ with DMSO addition was smaller than that of G1 , which was due to the disruption of hydrogen bonds within the gel, thus reducing the rigidity of the gel network and enhancing the mobility.[29]