Heterogeneous Double Metal Cyanide Catalyzed Synthesis of Poly(ε-caprolactone) Polyols for the Preparation of Thermoplastic Elastomers
, Min-Woong Lee 1, Sang-Woo Park 1, Jae-Eon Jeong 1, Soo-Jeong Lee 1, Wenliang Song 2, PilHo Huh 1,* and Il Kim 1,*Round 1
Reviewer 1 Report
This paper reports on ring-opening polymerization of caprolactone using as heterogeneous catalyst Co/Zn cyanide (DMC) combined with several alcohol initiators. They then use the low-MW polymers to prepare thermoplastic elastomers.
Writing is clear, the story is consistent. The proposed catalysts do work but performance is not impressive. The amount of (unwanted) transesterification can apparently be controlled with the proper choice of the initiator. The authors suggest (p3) that the complexing agent used for the DMC synthesis can be used to tune the catalysis, but the variation shown in Table 1 is really marginal.'
The authors state that their data show the polymerization mechanism to be coordination polymerization. I believe this is too optimistic. The data are COMPATIBLE with coordination polymerization, but probably also with other mechanistic variations. This statement should be weakened.
The authors use an Arrhenius plot to extract an Eact for their reaction: a lot of experiments go into that. But then they surprisingly say nothing about this result. How does this Eact compare to other reported cases?
On the whole, I believe that this paper represents a solid but unspectacular set of data. Acceptance in "catalysts" is recommended.
Author Response
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Author Response.pdf
Reviewer 2 Report
This contribution from Huh, Kim et al, describes the addition of various initiators to a system generating PCL. The work has been well carried out but the big drawback is it has been submitted to Catalysts, and there is little in the paper describing the catalysts. In fact, there is a small sketch in scheme 1, whilst characterization of the catalysts is in the supporting information. Most of the figures in the paper relate to the polymers and properties thereof. The situation is summed up by the conclusion, which has virtually no mention of the catalyst.
I would suggest a better place for this work is the journal Polymers.
Minor points:
Line 47 references 19, 20 are too limited.
From lines 138 to 143, clarify exactly which the NMR spectra the data comes from.
For Figure 2 (b), lost one Mn data point in the picture
In line 204, the “reaction rate” should change to conversion (i.e. %).
Figure 3, the NMR solvent is CD3OD, but PCL is usually precipitated using methanol so is this correct?
Scheme 1, the word format need to be changed.
In line 304, the Mn 5250 is different from Table 4: 5300
In line 391, after “(CL, 99%)” need space.
Throughout the paper use the present tense when talking about tables, figures etc.. e.g. line 96, are given… line 377 are summarized….
Note, I am not rejecting it because it has serious flaws, but because it does not fit the journal as mentioned above.
Author Response
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Reviewer 3 Report
Polycaprolactones (PCLs) with low molecular weights and relatively narrow PDIs synthesis were explored by ROP of CL catalyzed by the existing DMC catalysts based on their previous research. Kinetic studies were done to reveal the catalytical mechanism. And further functionality led to novel thermoplastic elastomer products. Overall, the paper would merit publication in Catalysts if the following issues were properly addressed by the authors.
1. Have to show the contents (formula structures) of the double metal cyanide in the Introduction.
2. The d-solvent indicated on all the 1H NMR spectra is not correct.
3. What does the * indicate on the 1HMR spectra? solvent (ethyl acetoacetate) peaks?
4. In Figure 1. please clear the figure by removing the chemical shifts, integration curves, and subtitle of each spectrum, expand them from 0.5 to 5.5 as well as name them as Figure 1a. 1b. and 1c.
5. Please show all the full spectra (including those in Figure 1.) showing NMR solvent peak (7.26) in the SI.
6. Please show the y axis of the 2D DOSY NMR spectrum, D or Log D? Also please rationalize the branched structure and the 2D DOSY signals.
7. The MALDI Mass spectra (Figure S11-S13) should be run 8 -10 instead of 5-7 in Table 1. Please be really careful with these correlated data.
8. Why some of the NMR Mn data were missing in Table 1.?
9. Error letters and graphs in Scheme 1. should be adjusted.
10. For the recycling exp showing in Figure S14., any XRD and IR data of the DMC catalysts after 1 or 2 cycles? What led to the XRD and IR signal change? Lose of the complexing agents?
11. How did the authors characterize the amount of the complexing agents that remained in the catalysts? Were they free or coordinated with the metals?
12. Did the authors screened the catalyst loadings of the polymerization reaction?
13. Any comments on the cobalt in the DMC catalyst? What's the function of this metal during the catalyzed ROP of CL?
14. If the PCL-TPE and PCL-TPU were first reported? Otherwise please do proper citation on them.
15. Please limit the self-citation ratio to 10%.
Author Response
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Round 2
Reviewer 2 Report
The paper is a marked improvement of the previous version as it now gives some details of the catalyst system. One last point to address is how do the compositions presented here compare with related catalysts used by others, e.g. those of Zhang et al.?
Author Response
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