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Open AccessArticle

Hydrosilylation vs. Piers–Rubinsztajn: Synthetic Routes to Chemically Cross-Linked Hybrid Phosphazene-Siloxane 3D-Structures

by Andrey S. Esin, Anna I. Chernysheva, Ekaterina A. Yurasova, Ekaterina A. Karpova, Vyacheslav V. Shutov, Igor S. Sirotin, Mikhail A. Soldatov, Mikhail V. Gorlov and Oleg A. Raitman

Polymers 2025, 17(14), 1967; https://doi.org/10.3390/polym17141967 - 17 Jul 2025

Viewed by 1187

Abstract

Exploration of new ways for the direct preparation of cross-linked structures is a significant problem in terms of materials for biomedical applications, lithium batteries electrolytes, toughening of thermosets (epoxy, benzoxazine, etc.) with interpenetrating polymer network, etc. The possibility to utilize hydrosilylation and Piers–Rubinsztajn [...] Read more.

Exploration of new ways for the direct preparation of cross-linked structures is a significant problem in terms of materials for biomedical applications, lithium batteries electrolytes, toughening of thermosets (epoxy, benzoxazine, etc.) with interpenetrating polymer network, etc. The possibility to utilize hydrosilylation and Piers–Rubinsztajn reactions to obtain cross-linked model phosphazene compounds containing eugenoxy and guaiacoxy groups has been studied. It was shown that Piers–Rubinsztajn reaction cannot be used to prepare phosphazene-based tailored polymer matrix due to the catalyst deactivation by nitrogen atoms of main chain units. Utilizing the hydrosilylation reaction, a series of cross-linked materials were obtained, and their properties were studied by NMR spectroscopy, FTIR, DSC, and TGA. Rheological characterizations of the prepared tailored matrices were conducted. This work showed a perspective of using eugenoxy functional groups for the preparation of three-dimensional hybrid phosphazene/siloxane-based materials for various applications. Full article

(This article belongs to the Section Polymer Chemistry)

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42 pages, 16363 KB

Open AccessReview

Tris(pentafluorophenyl)borane-catalyzed Hydride Transfer Reactions in Polysiloxane Chemistry—Piers–Rubinsztajn Reaction and Related Processes

by Slawomir Rubinsztajn, Julian Chojnowski and Urszula Mizerska

Molecules 2023, 28(16), 5941; https://doi.org/10.3390/molecules28165941 - 8 Aug 2023

Cited by 16 | Viewed by 7364

Abstract

Tris(pentafluorophenyl)borane (TPFPB) is a unique Lewis acid that catalyzes the condensation between hydrosilanes (Si-H) and alkoxysilanes (Si-OR), leading to the formation of siloxane bonds (Si-OSi) with the release of hydrocarbon (R-H) as a byproduct—the so-called Piers–Rubinsztajn reaction. The analogous reactions of hydrosilanes with [...] Read more.

Tris(pentafluorophenyl)borane (TPFPB) is a unique Lewis acid that catalyzes the condensation between hydrosilanes (Si-H) and alkoxysilanes (Si-OR), leading to the formation of siloxane bonds (Si-OSi) with the release of hydrocarbon (R-H) as a byproduct—the so-called Piers–Rubinsztajn reaction. The analogous reactions of hydrosilanes with silanols (Si-OH), alcohols (R-OH), ethers (R-OR′) or water in the presence of TPFPB leads to the formation of a siloxane bond, alkoxysilane (Si-OR or Si-OR′) or silanol (Si-OH), respectively. The above processes, often referred to as Piers–Rubinsztajn reactions, provide new synthetic tools for the controlled synthesis of siloxane materials under mild conditions with high yields. The common feature of these reactions is the TPFPB-mediated hydride transfer from silicon to carbon or hydrogen. This review presents a summary of 20 years of research efforts related to this field, with a focus on new synthetic methodologies leading to numerous previously difficult to synthesize well-defined siloxane oligomers, polymers and copolymers of a complex structure and potential applications of these new materials. In addition, the mechanistic aspects of the recently discovered reactions involving hydride transfer from silicon to silicon are discussed in more detail. Full article

(This article belongs to the Special Issue New Boron Chemistry: Current Advances and Future Prospects)

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15 pages, 1028 KB

Open AccessArticle

Starch/Silicone Elastomers and Foams

by Yang Chen, David A. Valentini and Michael A. Brook

Sustainability 2023, 15(13), 9941; https://doi.org/10.3390/su15139941 - 22 Jun 2023

Cited by 7 | Viewed by 3645

Abstract

While the beneficial physical properties of silicone polymers are exploited in many sustainable applications, the high energy requirement for their synthesis compromises to a degree their sustainability. We report a strategy to mitigate this issue by filling the silicone with inexpensive and renewable [...] Read more.

While the beneficial physical properties of silicone polymers are exploited in many sustainable applications, the high energy requirement for their synthesis compromises to a degree their sustainability. We report a strategy to mitigate this issue by filling the silicone with inexpensive and renewable starch. Elastomeric materials with covalently grafted starch, utilizing anhydride-modified silicones, permits loading of up to about 75% starch while maintaining many of the properties of the silicone. Alternatively, 50 wt.% starch-filled silicone foams can be prepared simply by mixing powdered starch with a mixture of HSi-functional silicone fluids in the presence of B(C₆F₅)₃. The physical properties of the resulting foams are determined by the quantity of SiH, which controls the final density of the foams (ranging from 0.258–0.875 g mL⁻¹), their Young’s modulus, and their degree of elasticity; both rigid and flexible foams were prepared. Materials with a high natural and renewable material content better adhere to green chemistry principle 7, should enhance the ease of degradation at end of life, and augment the sustainability of these silicone composites. Full article

(This article belongs to the Special Issue Advanced Polymeric Materials for Sustainability and Innovations)

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14 pages, 2615 KB

Open AccessArticle

Chelating Silicone Dendrons: Trying to Impact Organisms by Disrupting Ions at Interfaces

by Miguel Melendez-Zamudio, Kevina Chavda and Michael A. Brook

Molecules 2022, 27(6), 1869; https://doi.org/10.3390/molecules27061869 - 14 Mar 2022

Cited by 10 | Viewed by 3096

Abstract

The viability of pathogens at interfaces can be disrupted by the presence of (cationic) charge and chelating groups. We report on the synthesis of silicone dendrimers and linear polymers based on a motif of hexadentate ligands with the ability to capture and deliver [...] Read more.

The viability of pathogens at interfaces can be disrupted by the presence of (cationic) charge and chelating groups. We report on the synthesis of silicone dendrimers and linear polymers based on a motif of hexadentate ligands with the ability to capture and deliver metal ions. Mono-, di- or trialkoxysilanes are converted in G1 to analogous vinylsilicones and then, iteratively using the Piers-Rubinsztajn reaction and hydrosilylation, each vinyl group is transformed into a trivinyl cluster at G2. The thiol-ene reaction with cysteamine or 3-mercaptopropionic acid and the trivinyl cluster leads to hexadentate ligands 3 × N–S or 3 × HOOC–S. The compounds were shown to effectively capture a variety of metals ions. Copper ion chelation was pursued in more detail, because of its toxicity. On average, metal ions form chelates with 2.4 of the three ligands in a cluster. Upon chelation, viscous oils are converted to (very) soft elastomers. Most of the ions could be stripped from the elastomers using aqueous EDTA solutions, demonstrating the ability of the silicones to both sequester and deliver ions. However, complete ion removal is not observed; at equilibrium, the silicones remain ionically crosslinked. Full article

(This article belongs to the Special Issue Dendrimers for Biomedical Applications)

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15 pages, 3083 KB

Open AccessReview

Main Group Catalysis: Cationic Si(II) and Ge(II) Compounds as Catalysts in Organosilicon Chemistry

by Elke Fritz-Langhals

Reactions 2021, 2(4), 442-456; https://doi.org/10.3390/reactions2040028 - 19 Oct 2021

Cited by 16 | Viewed by 5246

Abstract

Cyclopentadienyl (Cp)-coordinated cationic Si(II) (1) and Ge(II) compounds (2) are a new class of catalysts for various transformations in organosilicon chemistry. This review demonstrates that these compounds effectively catalyze technically important reactions, such as the hydrosilylation of carbon-carbon multiple [...] Read more.

Cyclopentadienyl (Cp)-coordinated cationic Si(II) (1) and Ge(II) compounds (2) are a new class of catalysts for various transformations in organosilicon chemistry. This review demonstrates that these compounds effectively catalyze technically important reactions, such as the hydrosilylation of carbon-carbon multiple bonds and various types of siloxane-coupling reactions, e.g., the Piers-Rubinsztajn reaction and the oxidative siloxane coupling reaction. Whereas the cationic Si(II) compounds are sensitive to air and moisture, the corresponding cationic Ge(II) compounds are bench stable, thus offering further advantages. The new catalysts contribute to the growing need for the substitution of transition metals and heavier main group metals by their lighter congeners, especially in industrially relevant organosilicon chemistry. Full article

(This article belongs to the Special Issue Feature Papers in Reactions in 2021)

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14 pages, 616 KB

Open AccessArticle

Naturally Derived Silicone Surfactants Based on Saccharides and Cysteamine

by Adrien Lusterio and Michael A. Brook

Molecules 2021, 26(16), 4802; https://doi.org/10.3390/molecules26164802 - 8 Aug 2021

Cited by 20 | Viewed by 4331

Abstract

Silicone surfactants are widely used in many industries and mostly rely on poly(ethylene glycol) (PEG) as the hydrophile. This can be disadvantageous because commercial PEG examples vary significantly in polydispersity—constraining control over surface activity of the surfactant—and there are environmental concerns associated with [...] Read more.

Silicone surfactants are widely used in many industries and mostly rely on poly(ethylene glycol) (PEG) as the hydrophile. This can be disadvantageous because commercial PEG examples vary significantly in polydispersity—constraining control over surface activity of the surfactant—and there are environmental concerns associated with PEG. Herein, we report a three-step synthetic method for the preparation of saccharide-silicone surfactants using the natural linker, cysteamine, and saccharide lactones. The Piers–Rubinsztajn plus thiol-ene plus amidation process is attractive for several reasons: if employed in the correct synthetic order, it allows for precise tailoring of both hydrophobe and hydrophile; it permits the ready utilization of natural hydrophiles cysteamine and saccharides in combination with silicones, which have significantly better environmental profiles than PEG; and the products exhibit interesting surface activities. Full article

(This article belongs to the Section Green Chemistry)

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10 pages, 5266 KB

Open AccessCommunication

Vinyl-Functionalized Janus Ring Siloxane: Potential Precursors to Hybrid Functional Materials

by Thanawat Chaiprasert, Yujia Liu, Nobuhiro Takeda and Masafumi Unno

Materials 2021, 14(8), 2014; https://doi.org/10.3390/ma14082014 - 16 Apr 2021

Cited by 15 | Viewed by 4616

Abstract

A vinyl-functionalized all-cis-tetrasiloxycyclotetrasiloxane [ViSi(OSiMe₂H)O]₄ (Vi = vinyl group) Janus precursor was prepared from potassium cyclotetrasiloxane silanolate. The Janus precursor was selectively modified at its dimethylhydrosilyl groups [–SiMe₂H] via the Piers–Rubinsztajn reaction to obtain a family of [...] Read more.

A vinyl-functionalized all-cis-tetrasiloxycyclotetrasiloxane [ViSi(OSiMe₂H)O]₄ (Vi = vinyl group) Janus precursor was prepared from potassium cyclotetrasiloxane silanolate. The Janus precursor was selectively modified at its dimethylhydrosilyl groups [–SiMe₂H] via the Piers–Rubinsztajn reaction to obtain a family of new tetravinyl-substituted Janus rings [ViSi(OR’)O]₄ containing various functional groups in moderate yields. Remarkably, the tetravinyl groups on the structure remained intact after modification by the Piers–Rubinsztajn reaction. Since these synthesized compounds possess multiple functional groups (up to eight per molecule), they are potential precursors for advanced hybrid organic-inorganic functional materials. Full article

(This article belongs to the Special Issue Silsesquioxanes—Precursors to Functional Materials: Synthesis and Applications—a Themed Issue to Honor Professor Bogdan Marciniec on the Occasion of His 80th Birthday)

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16 pages, 3457 KB

Open AccessArticle

Spatially Controlled Highly Branched Vinylsilicones

by Mengchen Liao, Yang Chen and Michael A. Brook

Polymers 2021, 13(6), 859; https://doi.org/10.3390/polym13060859 - 11 Mar 2021

Cited by 4 | Viewed by 4042

Abstract

Branched silicones possess interesting properties as oils, including their viscoelastic behavior, or as precursors to controlled networks. However, highly branched silicone polymers are difficult to form reliably using a “grafting to” strategy because functional groups may be bunched together preventing complete conversion for [...] Read more.

Branched silicones possess interesting properties as oils, including their viscoelastic behavior, or as precursors to controlled networks. However, highly branched silicone polymers are difficult to form reliably using a “grafting to” strategy because functional groups may be bunched together preventing complete conversion for steric reasons. We report the synthesis of vinyl-functional highly branched silicone polymers based, at their core, on the ability to spatially locate functional vinyl groups along a silicone backbone at the desired frequency. Macromonomers were created and then polymerized using the Piers–Rubinsztajn reaction with dialkoxyvinylsilanes and telechelic HSi-silicones; molecular weights of the polymerized macromonomers were controlled by the ratio of the two reagents. The vinyl groups were subjected to iterative (two steps, one pot) hydrosilylation with alkoxysilane and Piers–Rubinsztajn reactions, leading to high molecular weight, highly branched silicones after one or two iterations. The vinyl-functional products can optionally be converted to phenyl/methyl-modified branched oils or elastomers. Full article

(This article belongs to the Special Issue Organosilicon Polymers: From New Structures towards New Properties)

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14 pages, 2603 KB

Open AccessCommunication

When Attempting Chain Extension, Even Without Solvent, It Is Not Possible to Avoid Chojnowski Metathesis Giving D₃

by Mengchen Liao, Yang Chen and Michael A. Brook

Molecules 2021, 26(1), 231; https://doi.org/10.3390/molecules26010231 - 5 Jan 2021

Cited by 3 | Viewed by 3652

Abstract

A simple, mild and efficient method to prepare HSi- or HOSi-telechelic, high-molecular-weight polydimethylsiloxane polymers (to 41,600 g·mol⁻¹) using the one-shot hydrolysis of M^HM^H is reported; titration of the water allowed for higher molecular weights (to 153,900 g·mol⁻¹ [...] Read more.

A simple, mild and efficient method to prepare HSi- or HOSi-telechelic, high-molecular-weight polydimethylsiloxane polymers (to 41,600 g·mol⁻¹) using the one-shot hydrolysis of M^HM^H is reported; titration of the water allowed for higher molecular weights (to 153,900 g·mol⁻¹). The “living” character of the chain extension processes was demonstrated by adding a small portion of M^HM^H and B(C₆F₅)₃ (BCF) to a first formed polymer, which led to a ~2-fold, second growth in molecular weight. The heterogeneous reaction reached completion in less than 30 min, much less in some cases, regardless of whether it was performed neat or 50 wt% in dry toluene; homogeneous reactions in toluene were much slower. The process does not involve traditional redistribution, as judged by the low quantities (<3%) of D₄ produced. However, it is not possible to avoid Chojnowski metathesis from M^HDDM^H giving D₃, which occurs competitively with chain extension. Full article

(This article belongs to the Special Issue Various Aspects of Silicon Polymer Chemistry: A Themed Issue in Honor of Professor Julian Chojnowski on the Occasion of His 85th Birthday)

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14 pages, 1622 KB

Open AccessArticle

Hyperbranched Polycarbosiloxanes: Synthesis by Piers-Rubinsztajn Reaction and Application as Precursors to Magnetoceramics

by Huayu Zhang, Lei Xue, Jianquan Li and Qingyu Ma

Polymers 2020, 12(3), 672; https://doi.org/10.3390/polym12030672 - 17 Mar 2020

Cited by 19 | Viewed by 4749

Abstract

Silicon-containing hyperbranched polymers (Si-HBPs) have drawn much attention due to their promising applications. However, the construction of Si-HBPs, especially those containing functional aromatic units in the branched backbones by the simple and efficient Piers-Rubinsztajn (P–R) reaction, has been rarely developed. Herein, a series [...] Read more.

Silicon-containing hyperbranched polymers (Si-HBPs) have drawn much attention due to their promising applications. However, the construction of Si-HBPs, especially those containing functional aromatic units in the branched backbones by the simple and efficient Piers-Rubinsztajn (P–R) reaction, has been rarely developed. Herein, a series of novel hyperbranched polycarbosiloxanes were prepared by the P–R reactions of methyl-, or phenyl-triethoxylsilane and three Si–H containing aromatic monomers, including 1,4-bis(dimethylsilyl)benzene, 4,4′-bis(dimethylsilyl)-1,1′-biphenyl and 1,1′-bis(dimethylsilyl)ferrocene, using B(C₆F₅)₃ as the catalyst for 0.5 h at room temperature. Their structures were fully characterized by Fourier transform infrared spectroscopy, ¹H NMR, ¹³C NMR, and ²⁹Si NMR. The molecular weights were determined by gel permeation chromatography. The degrees of branching of these polymers were 0.69–0.89, which were calculated based on the quantitative ²⁹Si NMR spectroscopy. For applications, the ferrocene-linked Si-HBP can be used as precursors to produce functional ceramics with good magnetizability after pyrolysis at elevated temperature. Full article

(This article belongs to the Special Issue Silicon-Containing Polymers)

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13 pages, 1925 KB

Open AccessReview

Synthesis of Structurally Precise Polysiloxanes via the Piers–Rubinsztajn Reaction

by Xunjun Chen, Minghao Yi, Shufang Wu, Lewen Tan, Xin Ge, Ming He and Guoqiang Yin

Materials 2019, 12(2), 304; https://doi.org/10.3390/ma12020304 - 18 Jan 2019

Cited by 18 | Viewed by 9514

Abstract

Silicone materials are widely used, from daily life to the military industry. With the advancement of science and technology and the increasing demands of industry, the requirement for high-performance precise structural silicone materials has increased. Therefore, the most important aspect in this field [...] Read more.

Silicone materials are widely used, from daily life to the military industry. With the advancement of science and technology and the increasing demands of industry, the requirement for high-performance precise structural silicone materials has increased. Therefore, the most important aspect in this field is finding a breakthrough in the synthetic methods. In this review, the latest research developments in controllable morphological structure and composite structure optimized synthesis of silicone materials using the Piers–Rubinsztajn (PR) reaction are summarized. The advantages of the PR reaction compared with traditional synthetic routes to silicone materials are presented. The highly controllable spatial structure of silicone materials and the structural combination of biomass or inorganic materials with silicone materials results in an improvement in performance or function. The morphological control of more complex silicone materials and the synthesis of non-traditional silicone materials with composite structures through the PR reaction will be the main research directions for the development of silicone materials in the future. Full article

(This article belongs to the Section Materials Chemistry)

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12 pages, 2897 KB

Open AccessArticle

Fabrication of Reactive Poly(Phenyl-Substituted Siloxanes/Silsesquioxanes) with Si‒H and Alkoxy Functional Groups via the Piers–Rubinsztajn Reaction

by Minghao Yi, Xunjun Chen, Shufang Wu, Jianfang Ge, Xinhua Zhou and Guoqiang Yin

Polymers 2018, 10(9), 1006; https://doi.org/10.3390/polym10091006 - 10 Sep 2018

Cited by 21 | Viewed by 5766

Abstract

Poly(phenyl-substituted siloxanes/silsesquioxanes) are obtained by the Piers–Rubinsztajn (PR) reaction of hydrogen-containing siloxanes (HCS) with diphenyldialkoxysilanes such as diphenyldimethoxysilane and diphenyldiethoxysilane catalyzed by tris(pentafluorophenyl)borane. ²⁹Si nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography, and refractive index analysis revealed that apart from phenyl substituents [...] Read more.

Poly(phenyl-substituted siloxanes/silsesquioxanes) are obtained by the Piers–Rubinsztajn (PR) reaction of hydrogen-containing siloxanes (HCS) with diphenyldialkoxysilanes such as diphenyldimethoxysilane and diphenyldiethoxysilane catalyzed by tris(pentafluorophenyl)borane. ²⁹Si nuclear magnetic resonance (NMR) spectroscopy, gel permeation chromatography, and refractive index analysis revealed that apart from phenyl substituents and complex structures such as molecular bridges composed of D₂^Ph2[(C₆H₅)₂Si(OSi)₂], structures also existed in these polymers, having high refractive indexes (above 1.50) and high molecular weights (75.60 KDa·mol⁻¹). As revealed by thermogravimetric analysis, these polymers have high thermal stability as well, with temperature at 5% mass loss (T_5%) increasing by 182.5 °C and R_w (residual weight ratio) increasing by 5.17 times from 14.63% to 75.60%, as compared to HCS, exhibiting its potential application as resins for resisting strong heat. Such high-refractive-index and temperature-resistant poly(phenyl-substituted siloxanes/silsesquioxanes) with Si–H and alkoxy functional groups can be used as a good addition-type crosslinking agent with adhesion-promoting properties or a special curing agent that can solidify silicone materials through simultaneous addition and condensation reactions, which has potential application in the light-emitting diode (LED) packaging industry. Full article

(This article belongs to the Special Issue Processing and Molding of Polymers)

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14 pages, 11213 KB

Open AccessArticle

Hyperbranched Polysiloxanes Based on Polyhedral Oligomeric Silsesquioxane Cages with Ultra-High Molecular Weight and Structural Tuneability

by Ning Liu, Jianyi Yu, Yaoyong Meng and Yuzhou Liu

Polymers 2018, 10(5), 496; https://doi.org/10.3390/polym10050496 - 4 May 2018

Cited by 10 | Viewed by 6789

Abstract

Hyperbranched siloxane-based polymers with ultra-high molecular weight were synthesized by the Piers–Rubinsztajn reaction between octakis(dimethylsiloxy) octasilsesquioxane with different dialkoxysilanes, using tris(pentafluorophenyl) borane as the catalyst. The origin of the high molecular weight is explained by the high reactivity of the catalyst and strain [...] Read more.

Hyperbranched siloxane-based polymers with ultra-high molecular weight were synthesized by the Piers–Rubinsztajn reaction between octakis(dimethylsiloxy) octasilsesquioxane with different dialkoxysilanes, using tris(pentafluorophenyl) borane as the catalyst. The origin of the high molecular weight is explained by the high reactivity of the catalyst and strain energy of isolated small molecule in which all eight silane groups close into rings on the sides of a single cubic cage. The structural tuneability was further demonstrated by use of methyl(3-chloropropyl)diethoxysilane, which generates a polymer with similar ultra-high molecular weight. Introduction of phosphonate groups through the chloropropyl sites later leads to functionalized polymers which can encapsulate various transition metal nanoparticles. Full article

(This article belongs to the Special Issue Siloxane-Based Polymers)

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