Naturally Occurring Oxazole Structural Units as Ligands of Vanadium Catalysts for Ethylene-Norbornene (Co)polymerization
, Dawid Siodłak 1, Karolina Banaś 1, Katarzyna Halikowska 1, Sławomir Wierzba 2 and Karel Doležal 3,4Round 1
Reviewer 1 Report
The authors present the synthesis and ethylen-norbornene polymerization of Vanadium Complexes having oxazole moiety. They discussed not only structural analysis of complex but the microstructure of obtained polymer, the paper can be suitable for Catalysts.
However, since there are multiple typographical errors and typographical errors, it is necessary to correct them with great care. On the other hand, we think that additional data is unnecessary.
for example:
2.3.(. Co)polymer properties
Glass transition temperature (Tg) decreases with increasing NB content.
Author Response
Once again, thank you very much for your help.
Remark 1: However, since there are multiple typographical errors and typographical errors, it is necessary to correct them with great care.
Response: We improved the English language of the manuscript, in particular, connected with terminology.
Remark 2: On the other hand, we think that additional data is unnecessary. for example:
2.3.(. Co)polymer properties
Glass transition temperature (Tg) decreases with increasing NB content.
Response: The following changes were introduced in the main text: “2.3. Polymer properties” and “Glass transition temperature (Tg) increases with increasing NB content.”
Reviewer 2 Report
This paper reports an investigation on ethylene and norbornene copolymerization by new vanadium oxazole type catalyst activated by AlEt2Cl and ethyltrichloroacetate.
My main criticism on this paper regards the polymer characterization and description.
1. Page 4 line 8 “ relatively low Mw ( Mw = 180-410 x103 g/mol.)” Please remove relatively low from this sentence. Rather it should be emphasized that copolymers have lower Mw than polyethylene.
2. Page 4 line 11 “ DSC analysis shows a random structure of the copolymers (Figures S22-32)”
First Figures S25 and S29 regard polyethylenes, which are crystalline.
Moreover, please change the sentence as follows:” DSC analysis shows that copolymers are amorphous materials with a glass transition temperature (Tg) that decreases with…”
Moreover, the ΔH of crystallinity present in some copolymers should be added.
3. All copolymers prepared, as shown by 13C NMR spectra contain up to 32.4 mol% of norbornene, and are constituted by isolated and atactic alternating sequences.
No NN diads and NNN triads are present.
It is not possible to indicate in 13 CNMR spectra a signal of diad on C5, C6 and not on the other carbons. In my opinion all the small signals attributed at triad are impurities.
What is the signal at about 26.0 ppm and those at about 50 ppm in the figures of supporting materials?
In the supplementary information, the scale of enhancement in Figure S37 and S38 are shifted.
Thus, please read, study and cite the literature on 13C assignment of spectra of ethylene -norbornene copolymers, for example DOI: 10.1016/j.ccr.2005.06.019 and references therein, correct the text and prepare a figure with correct structure and assignment in the supplementary materials.
4. L1-V and L3-V give almost the same activity, N content, and copolymer molar masses.
The influence of catalyst structure should be commented.
English language needs to corrected. Some examples:
Page 1 line 3 after introduction “ polymer materials”
Page 1 line 4 after introduction “polyolefins constitute more than half of global synthetic polymers”
Page 1 line -4 “it is worth noticing” and not It is worth to notice
Author Response
Remark 1: 1. Page 4 line 8 “ relatively low Mw (Mw = 180-410 x103 g/mol.)” Please remove relatively low from this sentence. Rather it should be emphasized that copolymers have lower Mw than polyethylene.
Response: We agree with the Reviewer. The proper change was introduced in the text according to the remark.
Remark 2a: Page 4 line 11 “ DSC analysis shows a random structure of the copolymers (Figures S22-32)” First Figures S25 and S29 regard polyethylenes, which are crystalline.
Response: Thank you for this remark. Only Figures S22-24, S26-28, S30-32, which correspond to the copolymers, were mentioned in the text.
Remark 2b: Moreover, please change the sentence as follows:” DSC analysis shows that copolymers are amorphous materials with a glass transition temperature (Tg) that decreases with…”
Response: We agree with the Reviewer. The sentence was changed according to the remark.
Remark 2c: Moreover, the ΔH of crystallinity present in some copolymers should be added.
Response: The ΔH of crystallinity was added on the thermograms presented in Figures 22-24S in Supplementary Materials.
Remark 3: All copolymers prepared, as shown by 13C NMR spectra contain up to 32.4 mol% of norbornene, and are constituted by isolated and atactic alternating sequences. No NN diads and NNN triads are present. It is not possible to indicate in 13 CNMR spectra a signal of diad on C5, C6 and not on the other carbons. In my opinion all the small signals attributed at triad are impurities. What is the signal at about 26.0 ppm and those at about 50 ppm in the figures of supporting materials? In the supplementary information, the scale of enhancement in Figure S37 and S38 are shifted. Thus, please read, study and cite the literature on 13C assignment of spectra of ethylene -norbornene copolymers, for example DOI: 10.1016/j.ccr.2005.06.019 and references therein, correct the text and prepare a figure with correct structure and assignment in the supplementary materials.
Response: We must agree with the opinion of the Reviewer that the obtained copolymers consist of isolated and atactic alternating norbornene units. Therefore, the following changes were made: (i) the work of Leone et at. (J. Mol. Cat. A, 2016, 424, 220) and the work of Tritto et al. (2018) were cited, (ii) the scale of all 13C NMR spectra of copolymers were corrected in Supplementary Materials, (iii) Figure 3 was also changed, and (iv) the proper changes in the text were introduced. The signals at about 26 and 50 ppm, can be assigned to traces of solvents (CH3 of toluene and methanol, respectively), used during the synthesis and purification of copolymers.
Remark 4: L1-V and L3-V give almost the same activity, N content, and copolymer molar masses. The influence of catalyst structure should be commented.
Response: The catalyst L3-V is more active than L1-V in ethylene polymerization as well as in ethylene-norbornene copolymerization at higher NB concentration. Additionally, the copolymers from L3-V show melting temperatures, whereas those from L1-V not. The difference is longer -CH2- microblocks for those of L1-V, which is shown by DSC. A paragraph at the end of section 2.3 was added.
Remark 5: English language needs to corrected. Some examples:
Page 1 line 3 after introduction “polymer materials”
Page 1 line 4 after introduction “polyolefins constitute more than half of global synthetic polymers”
Page 1 line -4 “it is worth noticing” and not It is worth to notice.
Response: The text was corrected. Additionally, numerous small stylistic changes were introduced.
Once again, we would like to thank you very much for the valuable remarks.
Reviewer 3 Report
This work presents a catalyst derived from a natural occurring compound for ethylene-norbornene copolymerization. Especially, the authors prepared three types of ligands with different substituents. The characterizations of materials and results are acceptable. I would like to recommend the publication of this work in this journal after minor revision. The comments below should be addressed completely in the revised manuscript.
- On line 12 of page 4, “Glass transition temperature (Tg) decreases with increasing NB content.”, here would be “Glass transition temperature (Tg) increases with increasing NB content.” Please check.
- The number in section 4 on page 5 should be "3. Materials and Methods". Please correct.
- Regarding the amount of catalyst used in (co)polymerization, see Table 1 for 7.0*10-6mol, and Section 4.3 for 6.0*10-6mol, but according to the data in Table 1, the amount of catalyst should be 7.1*10-6mol. please confirm.
- For the characterization of the catalyst, it may be more appropriate to add a single crystal diagram.
Author Response
We would like to thank you very much for your help.
Remark 1: On line 12 of page 4, “Glass transition temperature (Tg) decreases with increasing NB content.”, here would be “Glass transition temperature (Tg) increases with increasing NB content.” Please check.
Response: Thank you for this remark. Obvious mistake. The work “decreases” was changed for “increase” in the sentence.
Remark 2: The number in section 4 on page 5 should be "3. Materials and Methods". Please correct.
Response: Thank you. The numeration of sections was corrected.
Remark 3: Regarding the amount of catalyst used in (co)polymerization, see Table 1 for 7.0*10-6mol, and Section 4.3 for 6.0*10-6mol, but according to the data in Table 1, the amount of catalyst should be 7.1*10-6mol. please confirm.
Response: Thank you. We confirm that the amount of catalyst should be 7.1*10-6mol. The changes were introduced both in Table 1 and Section 3.3.
Remark 4: For the characterization of the catalyst, it may be more appropriate to add a single crystal diagram.
Response: We have tried to obtain a single crystal of X-ray analysis, unfortunately, our efforts were not successful. To our best knowledge, there are only few literature reports in the CSD database, which correspond to vanadium complexes. The main obstacle is the high vulnerability of such complexes on oxygen and air moisture. The following sentence was introduced in the text: “Efforts to obtain crystal form of the complexes suitable for X-ray analysis were not successful.”
Round 2
Reviewer 2 Report
The authors have made of corrections required, now the paper can be accepted for publication in Catalysts
