This manuscript describes a comparative study of three chromophore-substituted NMP^2 initiators, with the aim of correlating chromophore structure with spectral response and polymerization control. While the subject matter falls within the scope of Polymer Chemistry, the reviewer does not find the present work sufficiently rigorous or innovative for publication in this journal. The experimental study is limited to a small set of initiators and lacks a clearly articulated, systematic design rationale, making the work appear largely incremental. More importantly, the manuscript contains multiple imprecise or incorrect descriptions of controlled radical polymerization concepts, which raise concerns about the mechanistic interpretation and the validity of the claims regarding “living” or controlled behavior. For these reasons, the reviewer’s overall assessment is negative, and the manuscript is not recommended for publication in its current form.
Detailed comments:
1. Page 4, line 4. In polymer chemistry, the terms “termination” and “terminated” usually imply irreversible chain death. In the context of controlled radical polymerization, this wording is therefore inaccurate. The authors should revise this description to “temporarily deactivated” or “rendered dormant,” since these terms more appropriately describe the reversible capping of propagating radicals and the preservation of chain-end activity.
2. Pages 13-15, Figure 3 and Table 1. The presentation of the UV–Vis data requires clarification. In UV–Vis measurements, sample concentrations are typically adjusted to keep absorbance values within a reliable instrumental range. However, in Figure 3, the absorbance intensities of the synthesized NMP^2 initiators are much lower than those of the conventional photoinitiators (DMPA and BAPO), whereas Table 1 reports molar absorptivity values, which should in principle account for concentration effects. As currently presented, the relationship between the spectra in Figure 3 and the values listed in Table 1 is not sufficiently clear, and this makes the data difficult to interpret. The authors should clarify whether the spectra shown in Figure 3 are raw absorbance spectra or have been processed in any way, and how the molar absorptivity values in Table 1 were determined from these measurements. One possible way to improve Figure 3 would be to normalize the spectra to their respective maximum absorbance values if the purpose is to compare spectral shape and absorption range qualitatively, while relying on Table 1 for quantitative comparison of absorptivity.
3. Page 13. The statement that “NMP^2 3 and 4 initiators exhibit an expanded absorption wavelength range” should be revised or better qualified. According to Table 1, the molar absorptivity of initiator 3 at 405 nm is only 3 M^-1 cm^-1, which is essentially negligible, especially when compared with the much more substantial value of 327 for initiator 4. On this basis, the reviewer does not find it appropriate to present initiator 3 as meaningfully exhibiting expanded absorption into this wavelength region. The authors should either limit this statement to initiator 4 or provide a more careful qualification distinguishing weak detectable absorption from practically significant spectral extension.
4. Page 19. The statement that “These altered polymerization rates observed from NMP^2-initiated photopolymerization are consistent with the inherently reversible nature of NMP processes” is too broad and should be refined. A slower polymerization rate, by itself, does not constitute sufficient evidence for the reversible deactivation nature of NMP, since polymerization rate can also be influenced by other factors such as initiation efficiency and photolysis rate. The authors should therefore avoid presenting reduced rate alone as mechanistic support for reversible control and instead provide a more careful interpretation of what can and cannot be concluded from these kinetic profiles. In addition, the phrases “temporarily halting chain growth” and “allowing reinitiation with monomer” are mechanistically imprecise in the context of controlled radical polymerization. The relevant process is more accurately described as reversible deactivation/activation of propagating chains rather than repeated termination/reinitiation events. The wording in this section should therefore be revised accordingly, and the current overinterpretation should be removed.
5. Page 20, Figure 6. Figure 6 appears to show fitted kinetic curves rather than the original data plots. The authors should provide the raw kinetic plots as well. In addition, the DMPA control reaches >94% conversion within ~20 s, which is characteristic of rapid but uncontrolled radical polymerization and should be discussed accordingly. The fitted DMPA curve is not particularly informative and it is suggested to be removed.
6. Page 21. The phrase “enabling repeated termination and reinitiation events” is mechanistically incorrect. In the context of NMP, the process should be described as reversible deactivation and reactivation during chain propagation, not repeated termination and reinitiation.
7. Page 22, Figure 7. Figure 7 is difficult to read because the NMR spectra are heavily overlaid. In addition, the reviewer does not agree with the interpretation that correlates vinyl proton peak resolution/broadening with the controlled nature of the polymerization. These spectral changes are not, by themselves, convincing evidence of controlled radical polymerization.
8. Pages 24-25, Figure 9. A similar issue arises here as in Figure 6: the figure appears to show fitted lines without the underlying experimental data, and the original kinetic plots should also be provided. In addition, if the purpose of Figure 9 is to demonstrate pseudo-first-order kinetics, the key evidence is the linearity of ln([M]0/[M]) versus time. A separate monomer conversion versus time presentation is not necessary in this figure and may be omitted to improve clarity.
Some additional minor suggestions.
a. Page 2, Abstract. The full name of the DMPA photoinitiator should be given at first mention in the Abstract.
b. Page 3. Add “polymerization” after “reversible addition-fragmentation chain transfer (RAFT)” for accuracy and consistency.
c. Page 3. For the statement “…, mitigating the occurrence of undesired side reactions during the polymerization process,” the authors should provide an appropriate supporting reference.
d. Page 5. In “t-butyl”, t should be italicized.
e. Page 7. In “4-Aminobenzophenone”, the “A” should not be capitalized.