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Project titleSynthesis of heat- and frost-resistant amphiphilic polysiloxanes as promising materials for a new generation of high-tech appliences, devices and mechanisms.

AffiliationA.N. Nesmeyanov Institute of Organoelement Сompounds of Russian Academy of Sciences,

Research area 03 - CHEMISTRY AND MATERIAL SCIENCES, 03-102 - Synthesis, structure and reactivity of ferrous and organoelemental compounds

KeywordsSiloxanes, peroxides, macrocycles, polyorganosiloxanes, alkoxysilanes, chlorosilanes, aryl silanes, materials, homogeneous catalysis, oxidation, reduction, heat resistance, mechanical strength, amphiphilicity

Annotation
Polysiloxanes constitute a popular and widely used class of materials. Polyorganosiloxanes have a special place among these compounds due to a number of unique physicochemical properties: low glass transition temperature (down to −120 оC) along with high thermal stability (up to 350 оС); low saturated vapor pressure; hydrophobicity; small dependence of viscosity on temperature; considerable compressibility; low surface tension; gas permeability; biocompatibility, etc., so they are widely used in various fields of science, technology, medicine, etc. However, polyorganosiloxanes have two main drawbacks that restrict their applicability, namely, low mechanical strength and incompatibility with organic polymers. To overcome these drawbacks, a general approach is used that involves incorporation of “polar” functional groups (−С(O)OH, −C(O)R, −C(O)NH2, −CN, −OH, −NH2, −NO2, etc.) into the organic substituent. This results in strengthening of intermolecular interactions between the polymeric chains and thus imparts mechanical strength to materials on their basis and also increases their hydrophilicity. To date, just a few successful applications of this approach are known. On the one hand, they confirm the viability of this method, and on the other hand, this fact shows the scarcity of real synthetic methods aimed at solving this problem. Varying of the nature and number of “polar” functional groups within the organic substituents of polysiloxanes would make it possible to significantly expand the prospects of adjusting their properties and to obtain new-generation materials with higher surface energy. Moreover, it would open new prospects for the creation of unique electrically conducting (silicone electrolytes), liquid-crystal, self-healing and other hybrid materials. These materials will combine such properties as thermal and frost resistance with hydrophilicity and mechanical strength, which is a particularly topical task, for example, to create a new generation of aviation paint and varnish materials. It is important to note that previously silicone products have made a scientific breakthrough in the field of aviation and electrical engineering as binders of varnishes and enamels, but now they are almost replaced by organic analogues, just because of low physicomechanics. Obviously, the synthesis of polyorganosiloxanes with “polar” functional groups in an organic substituent requires monomers such as alkoxy-, chloro- and amino-organosilanes with the corresponding “polar” functions. Three main approaches to the synthesis of organosilicon products can be distinguished: (1) direct synthesis of chlorosilanes, (2) reaction of organolithium, organosodium and organomanganese compounds with chloro- and alkoxysilanes, (3) hydrosilylation of unsaturated compounds. These approaches do not allow functionalized organosilicon substrates with a “polar” functional groups within the organic substituents to be obtained. However, it might seem that “polar” functions can be incorporated into organosilicon products previously obtained by any of the three main methods mentioned above. Despite the apparent simplicity, this task has not been accomplished to date, except for a few examples. The thing is that the classical methods used in chemistry for incorporating “polar” functions into organic substituents prove to be inefficient for organosilicon substrates In view of this, the development of a general methodology for the preparation of chloro-, amino-, siloxy- and alkoxy-organosilanes with “polar” functional groups in an organic substituent remains an open problem. Thus, we can distinguish two main conceptual approaches to the synthesis of organosilanes with a “polar” functional group in the organic substituent. Let us consider these approaches using the synthesis of functionalized arylsilanes, that are the most promising research targets, as an example: (1) incorporation of a “polar” group into arylsilanes (a), modification of a “hidden” (alkyl, vinyl, allyl, etc.) functional group in arylsilanes into the corresponding “polar” group (b); (2) silylation of arenes containing a “polar” group to obtain the corresponding functionalized arylsilanes. The first approach (1) for synthesizing organosilanes with a “polar” function in the organic substituent was described above. As concerns the second approach (2): though there are numerous catalytic systems that allow the synthesis of various arylsilanes, they have mainly been developed for trialkylarylsilanes that are of no practical interest for the preparation of polyorganosiloxanes with “polar” functional groups within the organic substituents. Therefore, to create new types of heat- and frost-resistant, biocompatibility, self-healing, mechanically strong and amphiphilic polyorganosiloxane materials, it is necessary to develop a general methodology for the preparation of monomers: chloro-, amino-, siloxy- and alkoxy-organosilanes with "polar" functions in an organic substituent. Materials that combine heat- and frost-resistance with mechanical strength are extremely relevant in the creation of paint and varnish materials for aviation and space. This type of materials is designed for long-term and reliable protection of all aircraft components from large differences in atmospheric pressure, intensive exposure to ultraviolet radiation, aggressive impact of aviation-rocket fuels and, most importantly, from a sharp temperature drop. Based on the new organosilicon monomer base, it is possible to make a new step in the concrete struggle for the best complex of properties. It is important to note that this is only one of the most popular areas of application of thermo- and frost-resistant organosilicon products with increased physical and mechanical properties, where serious advantages over existing analogues can be obtained.

Expected results
We expect to develop and suggest general approaches to the synthesis of new types of monomers, namely, chloro-, amino-, siloxy- and alkoxy-organosilanes with “polar” functions in the organic substituent. Further, based on the unique set of monomeric reagents that will be obtained, we plan to perfect the techniques for synthesizing the corresponding polyorganosiloxanes that would combine mechanical strength and amphiphilicity with retention of their “basic” advantages, such as heat- and frost-resistance, as well as biological inactivity, gas permeability, etc. In turn, materials that combine heat- and frost-resistance with mechanical strength - are extremely important in obtaining paint and varnish materials (enamels) for aviation and space. Thus, the creation of paint and varnish materials, based on the polysiloxanes obtained, and their comparison with the currently known organic analogues based on polyurethanes, polyacrylates, etc., will confirm the operability of the main concept underlying the project - the introduction of the "polar" functional group in an organic substituent of polyorganosiloxanes will lead to an increase in mechanical properties, while preserving their "table" advantages. Since this project is aimed at solving not only some fundamental problems but also, in the first place, practically important ones, it is necessary that the entire way, from the development of approaches and synthesis of monomeric organosilicon substrates to the preparation of new types of silicones and materials on their basis, be based on the use of relatively simple and technologically advantageous reaction systems, as well as inexpensive and commercially available catalysts and reagents. In view of this, the success of this work would open up new prospects and opportunities for the use of silicones in the current fast-developing world, and would undoubtedly invoke keen interest from the perspective of further commercialization and industrialization of developments for creating a comfortable environment for human life.

Annotation of the results obtained in 2018
1. Aerobic Co‑/N‑Hydroxysuccinimide-Catalyzed Oxidation of p-Tolylsiloxanes to p-Carboxyphenylsiloxanes: Synthesis of Functionalized Siloxanes as Promising Building Blocks for Siloxane-Based Materials Synthesis of organosilicon products with a “polar” functional group within organic substituents is one of the most fundamentally and practically important challenges in today’s chemistry of silicones. In our study, we suggest a solution to this problem, viz., a high-efficiency preparative method based on aerobic Co-/N-hydroxysuccinimide (NHSI) catalyzed oxidation of p-tolylsiloxanes to p carboxyphenylsiloxanes. This approach is based on “green”, commercially available, simple, and inexpensive reagents and employs mild reaction conditions: Co(OAc)2/NHSI catalytic system, O2 as the oxidant, process temperature from 40 to 60 °C, atmospheric pressure. This reaction is general and allows for synthesizing both mono- and di-, tri-, and poly(p-carboxyphenyl)siloxanes with p-carboxyphenyl groups at 1,1-, 1,3-, 1,5-, and 1,1,1-positions. All the products were obtained and isolated in gram amounts (up to 5 g) and in high yields (80−96%) and characterized by NMR, ESI-HRMS, GPC, IR, and X-ray data: p-carboxyphenylsiloxanes in crystalline state form HOF-like structures. Furthermore, it was shown that the suggested method is applicable for the oxidation of organic alkylarene derivatives (Ar−CH3, Ar−CH2−R) to the corresponding acids and ketones (Ar−C(O)OH and Ar−C(O)−R), as well as hydride silanes ([Si]−H) to silanols ([Si]−OH). The possibility of synthesizing monomeric (methyl) and polymeric (siloxane-containing PET analogue, Sila-PET) esters based on 1,3-bis(p-carboxyphenyl)disiloxane was studied. These processes occur with retention of the organosiloxane frame and allow to obtain the corresponding products in 90 and 99% yields. Based on this material, an article was published: Goncharova I.K., Silaeva K.P., Arzumanyan A.V.*, Anisimov A.A., Milenin S.A., Novikov R.A., Solyev P.N., TkachevYa.V., Volodin A.D.,Korlyukov A.A., Muzafarov A.M. Aerobic Co- / N-hydroxysuccinimide- catalyzed oxidation of p-tolylsiloxanes to p-carboxyphenylsiloxanes: synthesis of functionalized siloxanes as promising building blocks for siloxane-based materials. J. Am. Chem. Soc., 2019, 141 (5), 2143–2151. DOI: 10.1021/jacs.8b12600 (IF = 14.357). Link: https://pubs.acs.org/doi/abs/10.1021/jacs.8b12600. Press releases: 1) Russian: (a) http://rscf.ru/ru/node/silikony-nauchilis-poluchat-pri-nizkikh-temperaturakh-s-pomoshchyu-vozdukha, (b) https://ria.ru/20190117/1549477429.html, (c) https://indicator.ru/news/2019/01/17/silikony-nizkie-temperatury-vozduh/; (2) English: (a) https://www.google.com/amp/s/phys.org/news/2019-01-silicones-temperatures-air.amp, (b) https://www.eurekalert.org/pub_releases/2019-01/arsc-soa012419.php, (c) http://rscf.ru/en/node/silicones-obtained-at-low-temperatures-with-the-help-of-air, (d) https://phys.org/news/2019-01-silicones-temperatures-air.html, (e) https://m.phys.org/news/2019-01-silicones-temperatures-air.html, (f) https://www.news-medical.net/news/20190125/Scientists-develop-new-method-for-synthesizing-para-carboxyplenylsiloxanes.aspx 2. [M] -catalyzed cross-coupling of hydride silanes with aryl halides - synthesis of functionalized aryl silanes We have investigated the possibility of obtaining functionalized organosilicon products using the cross-coupling reaction of hydride silanes and aryl halides. To study this process, triethylsilane and p-iodotoluene were chosen as model reagents. Optimization of the process conditions by the nature of the solvent, type of metal catalyst, additives, temperature and time of the process allowed us to find the optimal conditions for obtaining p-tolyltriethyl silane with a yield up to 90%. The application of the optimized conditions for the preparation of p-tolyltriethoxysilane, upon interaction of triethoxysilane with p-iodotoluene, made it possible to obtain the product with a yield up to 80%. Further, the optimal conditions were transferred to a wide range of hydride silanes containing one, two or three siloxy- or alkoxy-groups and functionalized aryl halides containing methyl, trifluoromethyl-, methylcarboxyl-, nitrile-, and other groups to obtain functionalized aryl silanes of various structures. Functionalized aryl silanes were obtained with yields up to 96%. Based on this material, an article is being prepared for publication.

Publications

1. Irina K. Goncharova, Kseniia P. Silaeva, Ashot V. Arzumanyan,* Anton A. Anisimov, Sergey A. Milenin, Roman A. Novikov, Pavel N. Solyev, Yaroslav V. Tkachev, Alexander D. Volodin, Alexander A. Korlyukova, and Aziz M. Muzafarova Aerobic Co-/N-Hydroxysuccinimide-Catalyzed Oxidation of p-Tolylsiloxanes to p-Carboxyphenylsiloxanes: Synthesis of Functionalized Siloxanes as Promising Building Blocks for Siloxane-Based Materials Journal of the American Chemical Society, 141 (5), pp 2143–2151 (year - 2019) https://doi.org/10.1021/jacs.8b12600

2. - Силиконы научились получать при низких температурах с помощью воздуха РНФ, - (year - )

3. - Российские ученые сделали силикон более дешевым и прочным РИА НОВОСТИ, - (year - )

4. - Силиконы научились получать при низких температурах с помощью воздуха ИДИКАТОР, - (year - )

5. - Silicones obtained at low temperatures with the help of air PHYS ORG, - (year - )

6. - Silicones obtained at low temperatures with the help of air EurekAlert, AAAS, - (year - )

7. - Silicones obtained at low temperatures with the help of air RSF, - (year - )

8. - Scientists develop new method for synthesizing para-carboxyplenylsiloxanes NEWS MEDICAL LIFE SCIENCES, - (year - )

9. - Ученые предложили «зеленый» метод получения силиконов ПОЛИТ.РУ, - (year - )

10. - Ученые предложили «зеленый» метод получения силиконов РНФ, - (year - )

Annotation of the results obtained in 2017
A highly efficient preparative method for synthesizing siloxanols based on aerobic [Co] or [Cu] / NHPI – catalyzed oxidation of hydride siloxanes has been suggested. The approach is based on “green”, commercially available, simple inexpensive reagents and employs mild reaction conditions: Co(OAc)2 or Cu(OAc)2 / NHPI catalytic system, О2 as the oxidant, process temperature from 25 to 60 оС, atmospheric pressure. This is a general reaction for the synthesis of both mono- and oligomeric siloxanols with various structures, namely, linear, branched and cyclic. Thus, siloxanols with terminal SiOH groups was obtained, which, it would seem, can be synthesized by hydrolysis of dichlorodimethylsilane, however, in this case, there remains reaction water, which creates serious problems in further application (in RTV (Room-Temperature-Vulcanizing) compositions, organosilicon resins, etc.). Thus, the aerobic oxidation of hydride siloxanes is a method of choice for the preparation of “dry” siloxanols. Furthermore, the method makes it possible to obtain unique oligosiloxanols with SiOH groups distributed along the (TMSO[(Me2SiO)10MeSiOH]11OTMS) chain, i.e. by setting the ratio of (Me2SiO)/(HMeSiO) units in the starting hydride siloxane, one can obtain siloxanol with the same ratio of (Me2SiO)/((HO)MeSiO) units without the condensation of the SiOH groups that are formed. This is a unique route to the synthesis of oligo- and polysiloxanols with SiOH groups distributed along the chain, which may be of considerable interest for making hydrophobic coatings, self-healing polymers and can be used as components of various formulations. The feasibility of using siloxanols as building blocks in the synthesis of siloxane structures, monodenrdons in particular, by a two-stage or in situ one-stage method (without isolation of a siloxanol) has been studied. This approach can be used to synthesize complex molecular systems with predefined structures. All siloxanols were obtained and isolated in gram amounts (0.5 – 15 g) in 58 – 98% yields according to GLC/NMR and 20 – 96% with respect to the isolated products and characterized using 1H, 13C, 29Si and 1H, 29Si – HMBC NMR spectroscopy, ESI-HRMS spectrometry, IR spectroscopy and GPC. The structure of bis(trimethylsiloxy)methylsilanol was additionally confirmed using single crystal X-ray diffraction analysis with in situ crystallization in thin glass capillary near the melting point. Based on this material, an article was published in the Green Chemistry journal (Arzumanyan A. V., Goncharova I. K., Novikov R. A., Milenin S. A., Boldyrev K. L., Solyev P. N., Volodin A. D., Smol’yakov A. F., Korlyukov A. A., Muzafarov A. M. Green Chem. 2018, 20, 1467-1471. DOI: 10.1039/C8GC00424B. Link: http://pubs.rsc.org/en/content/articlelanding/2018/gc/c8gc00424b/unauth#!divAbstract). Also, a highly efficient preparative method for synthesizing p-carboxyphenylsiloxanes based on aerobic [Co] / NHPI – catalyzed oxidation of p-tolylsiloxanes has been suggested. The approach is based on “green”, commercially available, simple inexpensive reagents and employs mild reaction conditions: Co(OAc)2 / NHPI catalytic system, О2 as the oxidant, process temperature from 30 to 60 оС, atmospheric pressure. This is a general reaction for the synthesis of mono- oligo- and polymeric p-carboxyphenylsiloxanes with various structures, namely, linear, branched and cyclic. Most p-carboxyphenylsiloxanes obtained in our work are unique and have not been described previously in the literature. The products were obtained and isolated in gram amounts (0.1 – 5 g) in 60 – 90% yields and characterized using 1H, 13C, 29Si and 1H, 29Si – HMBC NMR spectroscopy, ESI-HRMS spectrometry, IR spectroscopy and GPC. The structures of some substrates (4 products) have been confirmed using single crystal X-ray diffraction. Some p-carboxyphenylsiloxanes form hydrogen-bonded framework systems (Hydrogen-Bonded Organic Framework-HOF) having a pore size of 10-15 Å (the hydrogen-bonded supramolecular structure is preserved up to 250 ° C, as determined by the X-ray powder method, with temperatures ranging from +50 to +250 ° C in 50 ° C increments) with the possibility of restructuring the supramolecular structure with a decrease in temperature from 250 K to 100 K and high hydrophobicity. The synthesized p-carboxyphenylsiloxanes have a serious potential for the creation of a wide range of hybrid materials, metal–organic frameworks (MOFs), surfactants, self-healing materials, etc. Based on this material, an article is being prepared for publication. Published the section «Preparation of compounds with the Si–C bond», devoted to the methods of preparation of functionalized organosilicon monomers, within the framework of the chapter «Problems and prospects of development of chlorine-free methods for the formation of the silicon-element bond» in the review «Organoelement chemistry: promising areas of growth and challenges» in the Russian Chemical Reviews journal (Abakumov G. A., Piskunov A. V., Cherkasov V. K., Fedushkin I. L., Ananikov V. P., Eremin D. B., Gordeev E. G., Beletskaya I. P., Averin A. D., Bochkarev M. N., Trifonov A. A., Dzhemilev U. M.; Dyakonov,V. A.; Egorov M. P., Vereshchagin A. N.; Syroeshkin M. A., Jouikov V. V., Muzafarov A. M., Anisimov A. A., Arzumanyan A. V. Kononevich Yu. N., Temnikov M. N., Synyashin O. G., Budnikova Yu. H., Burilov A. R., Karasik A. A., Mironov V. F., Storozhenko P. A., Shcherbakova G. I., Trofimov B. A., Amosova S. V., Gusarova N. K., Potapov V. A., Shur V. B., Burlakov V. V., Bogdanov V. S., Andreev M. V. Russ. Chem. Rev. 2018, 87, 393-507. DOI: 10.1070/RCR4795. Link: http://www.uspkhim.ru/ukh_frm.phtml?jrnid=rc&page=forthcom).

Publications

1. Arzumanyan A.V. , Goncharova I.K. , Novikov R.A., Milenin S.A., Boldyrev K.L., Solyev P.N., Tkachev Y.V., Volodin A.D., Smol'yakov A.F., Korlyukov A.A., Muzafarov A.M. Aerobic Co or Cu/NHPI-catalyzed oxidation of hydride siloxanes: synthesis of siloxanols Green Chem., Royal Society of Chemistry, Green Chem., 2018, 20, 1467-1471 (year - 2018) https://doi.org/10.1039/C8GC00424B

2. Abakumov G.A., Piskunov A.V., Cherkasov V. K. et al. Organoelement chemistry: promising areas of growth and challenges Russ. Chem. Rev., Turpion Ltd, Russ. Chem. Rev. 2018, 87, 393-507 (year - 2018) https://doi.org/10.1070/RCR4795

3. Arzumanyan A.V. От элементарного кремния до функционализированных кремнийорганических мономеров, полимеров и материалов на их основе: проблемы и достижения VI научной молодежной школы-конференции «Химия, физика, биология: пути интеграции», Сборник тезисов докладов VI научной молодежной школы-конференции «Химия, физика, биология: пути интеграции». Россия, Москва, 18 – 20 апреля 2018 года. стр. 8 - 9. Пленарный доклад. (year - 2018)