Stimuli-responsive rotaxane-branched dendronized polymers with tunable thermal and rheological properties

Aiming at the creation of polymers with attractive dynamic properties, herein, rotaxane-branched dendronized polymers (DPs) with rotaxane-branched dendrons attached onto the polymer chains are proposed. Starting from macromonomers with both rotaxane-branched dendrons and polymerization site, targeted rotaxane-branched DPs are successfully synthesized through ring-opening metathesis polymerization (ROMP). Interestingly, due to the existence of multiple switchable [2]rotaxane branches within the attached dendrons, anion-induced reversible thickness modulation of the resultant rotaxane-branched DPs is achieved, which further lead to tunable thermal and rheological properties, making them attractive platform for the construction of smart polymeric materials.

6.It would be helpful to obtain calculation models for a part of the dendronized polymers before and after the acetate switching, to understand more any non-covalent interactions between each rotaxane-branched dendron on the polymer backbone.These results would correlate and support the claims of the rigidity of the polymers.
Reviewer #2: Remarks to the Author: In this manuscript, the authors demonstrated the design and synthesis of a new class of dendronized polymers with rotaxane-branched dendrons attached onto the linear polymer chains.Taking advantage of the switchable feature of [2]rotaxane branches, the controllable thickness modulation of the resultant rotaxane-branched dendronized polymers was successfully realized, thus providing a new strategy for the construction of smart polymeric materials.In particular, they creatively extended the mechanically interlocked macromolecules to a higher level and presented very interesting molecular architectures.Overall, this manuscript describes not only impressive polymer structures but also promising switching properties.I highly recommend its publication after some minor revisions: 1.The title was not so specific and seemed like a review paper.More keywords like, platinum-acetylide branch, acetate assembly, thermal and rheology properties, should be considered adding into the title.
Reply: Many thanks to reviewer 1 for this excellent suggestion.In the revised manuscript, the title has been modified as "Stimuli-responsive Rotaxane-branched Dendronized Polymers with Tunable Thermal and Rheological Properties", in which more keywords have been added.
2. The introduction part mainly described about the switching and stimuli-responsive features of rod-like dendronized polymers equipped with rotaxane interlocking moieties.What are the implications of the acetate ion assembly and disassembly from the dendronized polymer?It needs more introductory discussion and references for acetate ion sensing, for example.

Reply:
Based on the reviewer's excellent suggestion, the introductory discussion and references for potential acetate ion sensing have been added in the revised manuscript as follows:
4. In the titration experiment between dendronized polymers and TBA-acetate, what are the reasons of adding 5 equivalents of TBA-acetate for each urea unit?It will be better demonstrating the titration with, for example, 0.5, 1.0, 1.5, 2.0 to 5 equivalents to the dendronized polymers.Perhaps the switching, rigidity and physical properties of the resulting dendronized polymers are different and provided details of the solution switching properties.

According to the 1 H NMR titration experiments of PG1-PG3 that were recorded in THF-d8 at 298 K, for each [2]rotaxane unit, 5.0 equiv. of tetrabutylammonium acetate (TBAA) was needed to induce the translational motion of the pillar[5]arene macrocycle from urea station to the alkyl chain moiety in each [2]rotaxane branch…"
5. It would be interesting to characterize also the whereabout of the tetrabutylammonium (TBA) cation after delivering the acetate to the dendronized polymers.
Reply: Many thanks for the reviewer's helpful comment.After the addition of TBAA, acetate anions could bind with the urea moiety on the DPs through hydrogen bonding.
Since there is no interaction sites with TBA cations on the DPs, the TBA cations might locate around the acetate anions as countercations according to the following references： Angew.Chem. Int. Ed. 2007, 46, 6629-6633;Angew. Chem. Int. Ed. 2013, 52, 10270-  6.It would be helpful to obtain calculation models for a part of the dendronized polymers before and after the acetate switching, to understand more any non-covalent interactions between each rotaxane-branched dendron on the polymer backbone.These results would correlate and support the claims of the rigidity of the polymers.
Reply: According to the reviewer's insightful suggestion, the optimized structures of one repeat unit of rotaxane-branched DP PG1 before and after the addition of TBAA have been calculated with the aid of the MOPAC2016 program.As shown in Figure R5 (Supplementary Fig. 34 in the updated SI), remarkable stretching of the dendron is observed upon the addition of acetate anions as external stimulus.In the initial state, the distance of N1 (-CONCO-)-Si (TIPS) is 44.72 Å (Figure R5a).Upon the complexation with acetate anion that triggers the pillar[5]arene macrocycles to move from urea moiety to the alkyl chain station, the distance of N1 (-CONCO-)-Si (TIPS) become 54.15Å (Figure R5b), which indicates the cross-sectional radius (Rcs) values of the rotaxane-branched DP PG1 increase after the addition of acetate anions.These results further support the anion-induced thickness modulation process, therefore affecting the rigidity of the polymers.In the revised manuscript, a brief description has been added as follows: "…Along with the aforementioned reversible thickness modulation process that was further suggested by the structural optimization (Supplementary Fig. 34), the precise In particular, they creatively extended the mechanically interlocked macromolecules to a higher level and presented very interesting molecular architectures.Overall, this manuscript describes not only impressive polymer structures but also promising switching properties.I highly recommend its publication after some minor revisions: Reply: We greatly appreciate the reviewer's positive comments on our work.
1.All synthesis matters described in this manuscript were carried out on a high level, and this is an important accomplishment.As we know, sufficient amount of material is needed for practical uses.How large scale could the targeted rotaxane-branched dendronized polymers be synthesized?

Reply
Reply: According to the reviewer's excellent suggestion, the detailed investigations on the anion-induced switching features of the key monomers have been provided in the revised manuscript Supplementary Figs. 33,36 and 38 in the updated Supplementary Information).According to the results, these key monomers revealed similar reversible anion-induced switchable features with that of the corresponding rotaxane-branched DPs.Again we greatly appreciate the reviewers' thoughtful suggestions that obviously improved the quality of our manuscript.With these changes and responses, we hope the revised manuscript is now acceptable for publication in Nature Communications. --------
Figure R5.Optimized structures of one repeat unit of rotaxane-branched DP PG1 before (a) and after (b) the addition of TBAA as stimulus with the aid of the MOPAC2016 program.Analytical frequency computations were carried out at the same theoretical level for all stationary points to verify them as intermediate with no imaginary frequency.Structure volume and size variations were analyzed using Multiwfn Software.The visualization of the structures was generated by VMD software.