Review Reports

Round 1

Reviewer 1 Report

The authors, in this mini-review, have focused on the synthesis of EPDM on new-generation single-site catalytic systems based on Group IVB complexes. The authors have cited several relevant references to build up the present model's literature review. However, it is not sufficient. It is vast but not comprehensively focused on the significance of the metallocene and the synthesis of EPDM chosen in the manuscript. Authors should update the introduction and other sections by including recent articles published explicitly in the last two to three years. For example, 10.1016/j.jorganchem.2004.07.006, 10.1016/j.jorganchem.2020.121366, 10.1021/om1004447, 10.1002/pola.20292, 10.1080/10601325.2019.1674667, 10.1002/anie.201201598.  

Some points need to be addressed.

1.  Add single-site metallocene and dienes in the keywords

2.  In the first paragraph of the introduction author did not add the relevant references. Please check all references carefully throughout the manuscript.

3. Please give detailed mechanistic investigations to show how the anion is able to determine the activity and stereoselectivity of the catalyst. 

4. Describe the relationship of structure and nature of the counter anions that demonstrates the catalyst's molecular weight.

5. Describe the mechanistic steps for polymerizing EPDM by single-site catalysts, and how propylene and dienes are inserted or coordinated with catalyst.

6. Add at least one or two tables that exhibit the single-site catalysts productivities and properties of the resulting polymers.

7. Please add more recent examples of Constrained” Geometry Complexes (CGCs) in Figure 2

8.  Post-metallocenes are the most advanced catalysts for EPDM synthesis. A wide variety of metallocene structures makes it possible to control the resulting polymer (EPDM) properties; please give some metallocene examples used to develop unique elastomeric materials.

I am encouraging the authors to revise the manuscript according to the above suggestions that make it more interesting for the readers. And I think it could be published with major revisions.

Author Response

Dear Reviewer, 

We would like to express our appreciation for your comments and suggestions on our manuscript submitted for publication in Catalysts. Please, check our answers for your criticisms and suggestions.

 

“The authors have cited several relevant references to build up the present model's literature review.However, it is not sufficient. It is vast but not comprehensively focused on the significance of the metallocene and the synthesis of EPDM chosen in the manuscript. Authors should update the introduction and other sections by including recent articles published explicitly in the last two to three years (bold our).For example, 10.1016/j.jorganchem.2004.07.006, 10.1016/j.jorganchem.2020.121366, 10.1021/om1004447, 10.1002/pola.20292, 10.1080/10601325.2019.1674667, 10.1002/anie.201201598.”

 

Answer

It should be noted that the references  “10.1016/j.jorganchem.2004.07.006 (M. Bochmann, 2004);10.1002/pola.20292 (W. Kaminsky, 2004; 10.1002/anie.201201598 (H. Werner, 2012)”do not quite correspond to the subject of the proposed mini reviewas “new generation  for synthesis of ethylene-propylene-diene rubbers” which are of interest to companies, the main manufacturers of EPDM. However, the references 10.1021/om1004447 (M. Bochmann, 2010);10.3390/molecules26072037(A. Ali, 2021), 10.1039/D1RA06243C (A. Ali, 2021),and 10.1080/10601325.2019.1674667 (A.Ali, 2020) were added in corresponding part of the manuscript (paragraph below Figure 1).

 

1. Add single-site metallocene and dienes in the keywords

Answer

1. We have added your recommended additions to the keywords: “single-site catalysts; ethylene, propylene, diene, terpolymerization; EPDM; rubber”. In addition, according to the recommendation of the Reviewer 2 in the title of the article, the “IVB Groups catalysts” is inserted: “Homogeneous Group IVB catalysts of new generations for synthesis of ethylene-propylene-diene rubbers: a mini-review”.
2. In the first paragraph of the introduction author did not add the relevant references. Please check all references carefully throughout the manuscript.

Answer

2. Relevant references are added to the first paragraph of Introduction [Refs 1-4]. All references are carefully checked across the manuscript.

 

3. Please give detailed mechanistic investigations to show how the anion is able to determine the activity and stereoselectivity of the catalyst.
4. Describe the relationship of structure and nature of the counter anions that demonstrates the catalyst's molecular weight.
5. Describe the mechanistic steps for polymerizing EPDM by single-site catalysts, and how propylene and dienes are inserted or coordinated with catalyst.

Answer

3-5. This review was aimed at the analysis of published data (mainly presented by patent literature) on modern catalytic systems for the synthesis of EPDM (activities, comonomer incorporation, properties of EPDM, etc.). Such an interesting and wide area as the mechanistic aspects of copolymerization processes with diene is not included in the review. This is due to, firstly, to the scarcity of the information in the analyzed works and the failure of possibility of correct comparison, and, secondly, the mechanisms of metal-alkyl cation polymerization which are general for all monomers have been analyzed in detail in numerous earlier works and reviews on ethylene and a-olefins. Some of your questions on points 3-5 are discussed in our more detailed review [Ref. 4].

6. Add at least one or two tables that exhibit the single-site catalysts productivities and properties of the resulting polymers.

Answer

6. Initially, we were going to present such a table(s).However, on the basis of patent data, this turned out to be difficult, since it is not always possible to compare data on copolymerization under completely different conditions and kind of processes. For this reason, system activities, the levels of comonomer incorporation, and copolymer properties are reviewed for each catalytic system based on the data presented in patents. However, considering the remark of Reviewer 2, we completed the manuscript with a table containing EPDM manufacturers, their grades and the range of main characteristics. Unfortunately, more detailed specifications (such as catalytic systems and synthesis conditions) are not possible due to commercial confidentiality.
7. Please add more recent examples of Constrained” Geometry Complexes (CGCs) in Figure 2

Answer

7. Figure 2 shows two modern classes of CGC catalysts: bimetallic complexes (complex 5) and tetrahydroquinolinyl- and trihydroindolinyl-cyclopentadinyl titanium complexes (complexes 6). References to these complexes are quite recent: 2022 and 2016-2017, respectively. Unfortunately we have not found other new perspective classes of CGC catalysts in the literature.In the manuscript, we erroneously indicated reference 34 (46 in the revised version) to CGC catalysts. The error in the text of the manuscript has been corrected.

 

8. Post-metallocenes are the most advanced catalysts for EPDM synthesis. A wide variety of metallocene structures makes it possible to control the resulting polymer (EPDM) properties; please give some metallocene examples used to develop unique elastomeric materials.

Answer

8.The most unique and unusual materials obtained on Group IVB catalysts, in our opinion, are ultra-high molecular weight, long chain branched (LCB), and bimodal elastomers. The possibility of the formation of such materials is noted in the review for individual catalysts or classes.In particular, structures 1, 7-14 are effective for obtaining an ultrahigh molecular weight polymer and structures 6, 14 for synthesis of LCB elastomers.The analysis of grades of the leading EPDM manufacturers (Table) shows that all manufacturers can obtain EPDM with a wide range of properties, including ultra-high molecular weight, long chain branched, and bimodal elastomers. Unfortunately the type of catalyst is in more cases the subject of commercial confidentiality.

Reviewer 2 Report

This mini-review focuses on Group IVB complexes for synthesis of EPDM, especially patented and commercialized systems by major manufacturers. Given that EPDM is one of the most important polyolefin materials widely commercialized and used in various industries and the development of new metal catalysts is vital for synthesis of EPDM, this review could become a valuable reference for the community. The manuscript was well organized and presented. This reviewer recommends its publication in catalysts with the following issues addressed.

1) In title, Group IVB should be added before catalysts, since this review focuses on only group IVB complexes.

2) Since this review deals with patented and commercialized systems by major manufacturers of EPDM, it would be more helpful for the community if various brands and grades and properties and applications of EPDM by different manufactures can be provided and compared with eath other in a summerized Table.

3) An outlook should be given in the end.

Author Response

Dear Reviewer, 

We would like to express our appreciation for your comments and suggestions on our manuscript submitted for publication in Catalysts. Please, check our answers for your criticisms and suggestions.

 

Comments and Suggestions for Authors

This mini-review focuses on Group IVB complexes for synthesis of EPDM, especially patented and commercialized systems by major manufacturers. Given that EPDM is one of the most important polyolefin materials widely commercialized and used in various industries and the development of new metal catalysts is vital for synthesis of EPDM, this review could become a valuable reference for the community. The manuscript was well organized and presented. This reviewer recommends its publication in catalysts with the following issues addressed.

1) In title, Group IVB should be added before catalysts, since this review focuses on only group IVB complexes.

Answer

1. The title of the article has been changed according to your recommendation: “Homogeneous Group IVB catalysts of new generations for synthesis of ethylene-propylene-diene rubbers: a mini-review”.

 

2) Since this review deals with patented and commercialized systems by major manufacturers of EPDM, it would be more helpful for the community if various brands and grades and properties and applications of EPDM by different manufactures can be provided and compared with eath other in a summarized Table.

Answer

2. We completed the manuscript with a Table containing EPDM manufacturer, their grades and main properties. Unfortunately, more detailed specifications (such as catalytic systems and synthesis conditions) are not possible due to numerous grades of EPDMs (several dozen from each manufacturer) and commercial confidentiality.

 

3) An outlook should be given in the end.

Answer

3. As expected perspectives in the creation of new catalytic systems and new brands of EPDM we have added the sentence “The huge potential for tuning the structures of catalytic systems allows us to count on the further creation of new efficient systems for synthesis of EPDM and, accordingly, the production of elastomers with a high content of diene(s) and the creation of new polymer microstructures with an even wider range of properties” to section “Conclusions and Perspectives”.

Round 2

Reviewer 1 Report

The authors have paid significant attention to revising the manuscript according to the suggestions. I am happy and satisfied with the modifications and changes. I recommend the manuscript for publication in its current form.