Investigation and Comparison of Catalytic Methods to Produce Green CO₂-Containing Monomers for Polycarbonates

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article describes the synthesis of CO2-containing monomers for polycarbonates.  The insights of these investigations using two methods (high-pressure homogeneous catalytic condition and organocatalytic condition) seem to be useful and practical. The authors describe the answers for four questions focused by themselves. Furthermore, the ring-opening polymerization of some carbonates seems to be  a useful process for producing an amorphous thermoplastic polymer. These results seem to be acceptable for the article of catalysts.

Author Response

Thank you for your kind report

Reviewer 2 Report

Comments and Suggestions for Authors

The authors report a study related to the preparation of cyclic styrene carbonate through two catalytic methods. Additionally, the obtained monomer has been subsequently subjected to ring-opening polymerization (ROP). The reason why these particular methods have been selected for the synthesis of styrene carbonate should be more clearly explained, possibly comparing reaction conditions and outputs with other cited methodologies. Above all, results in term of yields of formation of cyclic styrene carbonate and the subsequent polycarbonate, need to be reported together with a suitable discussion of the obtained results. The manuscript can be suitable for publication on this journal after addressing the following revisions.  

1)    Quality of Figure 2 has to be improved.

2)    Figure 4 needs to be properly described.

3)    Comments on Table 1 and 2 related to the obtained yields have to be detailly discussed in the text.

Comments on the Quality of English Language

Minor editing of English language required

Author Response

Comments and Suggestions for Authors
The authors report a study related to the preparation of cyclic styrene carbonate through two catalytic methods. Additionally, the obtained monomer has been subsequently subjected to ring-opening polymerization (ROP). The reason why these particular methods have been selected for the synthesis of styrene carbonate should be more clearly explained, possibly comparing reaction conditions and outputs with other cited methodologies. Above all, results in term of yields of formation of cyclic styrene carbonate and the subsequent polycarbonate, need to be reported together with a suitable discussion of the obtained results. The manuscript can be suitable for publication on this journal after addressing the following revisions.
Question 1:
Quality of Figure 2 has to be improved.
Answer 1:
The Figure 2 was replaced by an updated version. The distances of the molecules have been reduced and the figure compressed.
Question 2:
Figure 4 needs to be properly described.
Answer 2:
Figure 4 was replaced by an updated version is now Figure 12. The description of the individual components was done, as minor additions in the text below the figure.
Question 3:
Comments on Table 1 and 2 related to the obtained yields have to be detailly discussed in the text.
Answer 3:
Table 1 and 2 were updated with the Yields of styrene carbonate and polymer for Table 1. The yield was described based on CO2 consumption for Table 1. The distinction between the linear portion and the cyclic portion cannot be derived from this and can only be described qualitatively. Table 2 were updated with the Yields of styrene carbonate base on 1H-NMR results and get discussed in text.
Question 4:
The reason why these particular methods have been selected for the synthesis of styrene carbonate should be more clearly explained, possibly comparing reaction conditions and outputs with other cited methodologies.
Answer 4:
We enlarged the introduction, explaining more clearly the methods selected for the
synthesis of styrene carbonate.
„ Due to strict environmental and safety requirements regarding the hazardous nature of phosgene, the
phosgenation route is not considered in this study. However, this route might be suitable in industry with the
appropriate equipment [26,27]. Therefore, only catalytic synthesis methods are considered, which already
provide good yields of 90% or more[21,22]. For the desired synthesis of monomer for a ring-opening
polymerization these routes need to be modified, as the complete separation of phenol and benzonitrile is very
demanding and not suitable for industrial processes, as it is only possible via column chromatography.
Therefore, the objective of this work is a solution to this problem by adapting the synthesis. One alternative is a
catalytic reaction of CO2 and styrene epoxide at elevated pressure. However, this synthesis has already proven
to be problematic in the literature, as problems with side reactions such as polymerization have been observed
here[28]. Therefore, yields of only between 60-90% were reported[11,22,24,29–32].“

Reviewer 3 Report

Comments and Suggestions for Authors

Cyclic carbonates monomers are required in ring-opening polymerizations , in this manuscript. The authors developed a new synthesis of cyclic carbonates, and applied to the preparation of thermoplastic materials, I think the work is meaningful, and publishable. there are still some problems, and my suggestion is to publish it after the minor revision.

1. There are discrepancies between the values in table 2 of the main text and table 1 of the supporting information, and there is no consistency in the number of decimal places retained.

2. The MRI images in the Supporting Information are not clear enough to observe the peak shapes and higher resolution images should be provided. The same should be true for the other images in the main text, please redraw them and label the figure notes correctly. e.g. representation of “Left” and “right” in Figure 8.

3. Table 1 in the main text contains experiments 18, 19 and 20 with consistent experimental parameters. Is this a writing error? If not, please explain the significance.

4. There are multiple formatting and presentation errors throughout the text. e.g.CO2 expression in Figure 34. Before submitting a revision be sure that your material is properly prepared and formatted, and that sentence grammar is not in question.

Author Response

Reviewer 3:
Comments and Suggestions for Authors
Cyclic carbonates monomers are required in ring-opening polymerizations, in this
manuscript. The authors developed a new synthesis of cyclic carbonates, and
applied to the preparation of thermoplastic materials, I think the work is meaningful,
and publishable. there are still some problems, and my suggestion is to publish it
after the minor revision.
Question 1:
There are discrepancies between the values in table 2 of the main text and table 1 of
the supporting information, and there is no consistency in the number of decimal places
retained.
Answer 1:
The tables were properly reworked and updated.
Question 2:
The MRI images in the Supporting Information are not clear enough to observe the
peak shapes and higher resolution images should be provided. The same should be
true for the other images in the main text, please redraw them and label the figure
notes correctly. e.g. representation of “Left” and “right” in Figure 8.
Answer 2:
All figures with more than 1 picture were updated. Care was taken to ensure that all
graphs were consistently labeled with the abbreviation a,b,c,d in order to provide a
better overview. Figures 8, 9, 12 and 13 (now Figure 4, 5, 6, 9, 10) have been adapted.
“ Identification of the polymeric (blue), linear (red) and cyclic (black) carbonate band through
(a) ATR-IR spectra (b) HPLC-ESI-DAD measurements.”
All MRI/NMR Spectra got replaced with higher resolution version in Paper and supporting
information. Figure 11 was replaced with figure 7 and 8 and more discussed in the Text
Question 3:
Table 1 in the main text contains experiments 18, 19 and 20 with consistent
experimental parameters. Is this a writing error? If not, please explain the significance.
Answer 3:
This is correct, since we tested in this experiments the change in total catalyst amount
under the condition, that the catalysts remain in the same ratio. Additionally, text was
added, describing this experiments.
“ Therefor experiments were carried out in which the amount of one catalyst species was
changed (Table 1, Experiment 12-17) and experiments in which the ratio of the catalysts was
kept constant, varying the total amount of the bifunctional catalyst (Table 1, Experiment 18-
20). It was found that the reaction to cyclic styrene carbonate strongly depends on the correct
ratios of the two catalysts, with the total amount of catalyst only influencing the reaction time.”
Question 4:
There are multiple formatting and presentation errors throughout the text. e.g.CO2
expression in Figure 34. Before submitting a revision be sure that your material is
properly prepared and formatted, and that sentence grammar is not in question.
Answer 4:
The document and supporting information were properly updated and revised.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Now the manuscript can be a suitable contribution for Catalysts.