Recommendation: consider after major revisions.
The manuscript by Guerre and colleagues reports a covalent adaptable network (CAN) based on a thiol-thioester exchange reaction, in which bond exchange and network robustness were tuned by cleverly masking via a thiol-Michael reaction. While this work represents an interesting strategy to address creep and permanent deformation in thiol-thioester-based CANs, the overall data provided are not very conclusive, and significant additions and revisions are needed before considering this manuscript for publication in Polymer Chemistry.
Major concerns
1) The authors haven’t provided enough consideration and conclusive evidence on the effect of dissociative thiol-Michael exchange in the network. While unmasked thiols can initiate thiol-thioester exchange, the thermally mediated dynamic exchange between thiols and Michael acceptors can’t be ignored. As reported by Konkolewicz et al., the retro-Michael reaction can be activated at relatively lower temperature (75 °C), while the addition of thiols to Michael acceptors is remarkably faster than the retro-Michael reaction, which may explain the slower relaxation observed within the masked network: as soon as “unmasked” thiols form, they react with the Michael acceptors.
https://doi.org/10.1039/C8OB00397A
A more in-depth exploration is recommended to understand the role of dynamic thiol-Michael exchange within the network regarding creep, stress relaxation, and reprocessability. This may include – NMR study of a model reaction of the dynamic thiol-Michael response with the dithioacetal at elevated temperature, and evaluation of the dynamic properties of a network with thiol-Michael linkers lacking moieties capable of thiol-thioester exchange. Additionally, the kinetics of free thiol release can be tuned based on the reactivity of the Michael acceptor (different electron withdrawing groups – ketone, ester, sulfone etc.

2) The authors mentioned that with the protection of thiol, a significant increase in crosslink density, hence Tg is increased compared to the free thiol network (-28.5 ºC vs 3.9 ºC). While creep profiles were measured at higher temperatures to mitigate the influence of crosslink density on the dynamic mechanical properties, this reviewer is not convinced that such significant differences in glass transition and swelling ratio will not influence their creep or stress relaxation behavior. At lower crosslink density, there will be more chain mobility, leading to more creep or faster stress relaxation. Hence, networks with comparable crosslink density and Tg should be studied. Additionally, stress-relaxation at room temperature for all networks should be reported.

3) Reprocessability properties of both networks (free and masked) should be studied and compared. As the authors reported, a color shift indicative of thiol oxidation was observed in the masked networks. A similar study should be performed with the free thiol network. Additionally, all these results and findings (including relaxation time, Tg, and activation energy) should be tabulated. The authors should comment on how this work represents a significant improvement over previously reported thiol-thioester-based CANs, despite the drawback of thiol oxidation within the networks after reprocessing.
Minor concerns:
1) The authors should clearly identify the exchange mechanisms of thiol-thioester and thiol-Michael exchange – associative or dissociative? This can be reflected in Scheme 1.
2) Proper literature citation should be provided for this statement – “Furthermore, the rapid base-catalysed thiol–thioester exchange observed at room temperature may result in pronounced creep, particularly in materials with lowglass transition temperature.”
3) For the NMR study of the model reactions, the molar concentration of all the components during the reaction and after reaching equilibrium should be reported.
4) The resolution of all the schemes can be improved.
5) It is recommended to use either “masked” or “blocked” thiol to retain consistency and avoid confusion.

Recommended for publication, satisfied with the revision.