Piers Rubinsztajn Research Articles

High Refractive Index, Enantiopure Silicones Based on BINOL.

The high refractive index aromatic compound, binaphthol (BINOL), is readily incorporated into silicone polymer chains using the Piers-Rubinsztajn (PR) reaction; alternating and random linear copolymers, and elastomers are available. The highest refractive index (RI) materials are BINOL rich. It is not possible to directly make high refractive index linear polymers with very short HSi-capped, telechelic silicone chains, as they do not react cleanly. However, chain extending short vinyl-capped BINOL macromers with simple arylsilanes using hydrosilylation leads to polymers with a molar mass of up to 8000 and refractive indices of up to 1.58. Elastomers are prepared using similar processes. The reactions are facile to practice and suggest BINOL can be harnessed in these and other processes to augment RI.

The ultimate Lewis acid catalyst: using tris(pentafluorophenyl) borane to create bespoke siloxane architectures.

The breadth of utility of a commercially available and stable strong Lewis acid catalyst, tris(pentafluorophenyl)borane, has been explored, highlighting its use towards a wide range of unique siloxane products and their corresponding applications. This article focuses on the variety of different outcomes that this impressive borane offers in controlled and selective manners by the variation of reaction conditions, precursor functionalities, reagent or catalyst loading, and the mechanistic considerations that contribute. With a predominant focus on the Piers-Rubinsztajn reaction and its modifications, tris(pentaflurophenyl)borane's utility is highlighted in the synthesis of linear, cyclic and macrocyclic siloxanes, aryl-/alkoxysiloxanes, and other bespoke products. The significance of the catalytic transformation within the field of siloxane chemistry is discussed alongside some of the challenges that arise from using the borane catalyst.

Thermo-curable and photo-patternable polysiloxanes and polycarbosiloxanes by a facile Piers–Rubinsztajn polycondensation and post-modification

A series of BCB-functionalized organosilicon materials were prepared by a facile Piers–Rubinsztajn polycondensation and Heck coupling post-modification method, rendering a simple and efficient option for advanced packaging dielectric materials.

Use of Piers-Rubinsztajn Chemistry to Access Unique and Challenging Silicon Phthalocyanines.

Axial functionalization is one mode that enables the solubility of silicon phthalocyanines (SiPcs). Our group observed that the use of typical axial functionalization methodologies on reaction of Cl2SiPc with the chlorotriphenyl silane reagent unexpectedly resulted in the equal formation of triphenyl silyloxy silicon tetrabenzotriazacorrole ((3PS)-SiTbc) and the desired bis(tri-phenyl siloxy)-silicon phthalocyanine ((3PS)2-SiPc). The formation of a (3PS)-SiTbc was unexpected, and the separation of (3PS)-SiTbc and (3PS)2-SiPc was difficult. Therefore, in this study, we investigated the use of Piers–Rubinsztajn (PR) chemistry as an alternative method to functionalize the axial position of a SiPc to avoid the generation of a Tbc derivative. PR chemistry is a novel method to form a Si–O bond starting with a Si–H-based reactant and a −OH-based nucleophile enabled by tris(pentafluorophenyl)borane as a catalyst. The PR chemistry was screened on several fronts on how it can be applied to SiPcs. It was found that the process needs to be run in nitrobenzene at a molar ratio and at a particular temperature. To this end, the triphenylsiloxy derivative (3PS)2-SiPc was produced and fully characterized, without the production of a Tbc derivative. In addition, we explored and outlined that the PR chemistry method can enable the formation of other SiPc derivatives that are inaccessible utilizing other established axial substitution chemistry methods such as (TM3)2-SiPc and (MDM)2-SiPc. These additional materials were also physically characterized. The main conclusion is that the PR chemistry method can be applied to SiPcs and yield several alternative derivatives and has the potential to apply to additional macrocyclic compounds for unique derivative formation.

Naturally Derived Silicone Surfactants Based on Saccharides and Cysteamine.

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.

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

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.

Spatially Controlled Highly Branched Vinylsilicones.

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.

Dumbbell‐Shaped, Graft and Bottlebrush Polymers with All‐Siloxane Nature: Synthetic Methodology, Thermal, and Rheological Behavior

Back Cover: In article number 2000645 by Ashot V. Arzumanyan and co-workers, a methodology for synthesizing dumbbell-shaped, graft and bottlebrush polymers with all-siloxane nature is suggested. They are synthesized from different generations and structure dendritic siloxanols and polyhydride-siloxanes by the Piers–Rubinsztajn reaction. The product physical properties are determined not only by the macromolecular structure, the linear chain length, the size and frequency of branched pendant, but also by the type of peripheral pendant substituents: Me or Et.

Revisiting the System Silanes-Polysaccharides: The Cases of THEOS-Chitosan and MeTHEOS-Chitosan.

The glycol alkoxysilanes, tetrakis(2-hydroxyethyl)silane (THEOS), and tris(2-hydroxyethyl)methyl silane (MeTHEOS) are water soluble derivatives of tetraethoxysilane (TEOS) and methyltriethoxysilane (MeTEOS) and precursors of the system silane-chitosan reviewed in this work. The glycol modified alkoxysilanes are obtained by transesterification reaction of TEOS or MeTEOS with ethylene glycol. The reaction evolution is monitored by 29 Si NMR. It is possible to observe the formation of the various species of glycol alkoxysilanes in equilibrium as the reaction proceeds showing that the oligomers formation is favored at longer reaction times with the final product tendency to gel keeping the complete water solubility. The glycol alkoxysilanes are synthesized at moderated reaction conditions, by using the Piers-Rubinsztajn (PR) reaction. Additionally, it is already known that THEOS is compatible with different natural polysaccharides as chitosan and the same behavior has been demonstrated in this work for MeTHEOS. Several reports refer studies regarding the system THEOS-polysaccharides to synthesize hybrid materials. The system THEOS-chitosan is known but the characterization as well as the way silane-chitosan interact has not been studied in detail. In the present report, chemical evidence of the covalent interactions THEOS- and MeTHEOS-chitosan based on NMR studies (13 C and 29 Si) are presented as intended.

Influence of the tetraalkoxysilane crosslinker on the properties of polysiloxane-based elastomers prepared by the Lewis acid-catalysed Piers-Rubinsztajn reaction

We investigate the influence of the tetrafunctional alkoxysilan R-groups, with a range of sterics and electronics. This is through a solvent free polysiloxane network formation under ambient conditions using Lewis acid catalysed Piers-Rubinsztajn (PR) reaction.

Transparent silphenylene elastomers from highly branched monomers

Catalyst free crosslinking of highly branched silphenylene monomers, made using the Piers–Rubinsztajn reaction, leads to high refractive index, soft elastomers.

Facile fabrication of eugenol-containing polysiloxane films with good optical properties and excellent thermal stabilityviaSi–H chemistry

Biomass-containing polysiloxane films that exhibit good optical properties and excellent thermal stability for encapsulation have been developedviathe Piers–Rubinsztajn reaction and Pt-catalysed hydrosilylation.

Reversible Redox Crosslinking of Thiopropylsilicones.

Most silicone elastomers are thermosets. As a response to the new paradigm of polymer recyclability, the development of silicone elastomers that can be reversibly and repeatedly cured and uncrosslinked using redox conditions is reported. Thiopropyl-modified silicones are oxidized to elastomers with disulfide crosslinks using the organosoluble oxidant PhI(OAc)2 . As with any elastomer, mechanical properties can be tuned by varying crosslink density. Thermal stabilities in air show that the products are comparable to traditional silicone thermosets, with degradation only starting over 300°C. Uncrosslinking back to the same thiopropyl-modified silicones involves reductive S-S bridge cleavage using a Piers-Rubinsztajn reaction with hydrosilanes catalyzed by B(C6 F5 )3 ; HSiMe2 OSiMe3 is identified as a convenient reducing agent. The initially formed silicone-(CH2 )3 S-SiMe2 OSiMe3 products need deprotection with water in isopropanol/water to completely regenerate the thiopropylsilicones. This oxidation/reduction crosslinking/uncrosslinking cycle is practiced thrice, with a yield of 89% per cycle, with essentially no change in the Young's moduli of the elastomers, or 1 H NMR spectra of the uncrosslinked fluids after reduction. Further oxidation of disulfide groups on the elastomer surface permanently and significantly improved water wettability.

Synthesis and comparison of the rheological and thermal properties of acyclic and polycyclic forms of polyphenylsilsesquioxane

In this work, we present a synthesis of a non-functional acyclic form of polyphenylsilsesquioxane (a-PPSQ) by the Piers–Rubinsztajn reaction of hyperbranched polyphenylethoxysiloxane (PPEOS) with dimethylphenylsilane.The polycyclic form of PPSQ (pc-PPSQ) was obtained by hydrolytic polycondensation of PPEOS in acetic acid followed by addition of dimethylphenylethoxysilane as the blocking agent.The rheological and thermal properties of acyclic and polycyclic forms of PPSQ were compared.All the PPSQs have high heat resistance (T5% weight loss) ranging from 405 to 480 °C in air and up to 500 °C in an inert environment. The glass transition temperature (Tg) of a-PPSQ is significantly lower (−34 °C) than in pc-PPSQs where Tg = 29–104 °C for pc-PPSQs with MW = 1400–5050.It was demonstrated that both a-PPSQ and pc-PPSQ offer Newtonian flow behavior. a-PPSQ with a molecular weight (MW) of 2150 has the lowest dynamic viscosity of ~0.38 Pa*s, whereas that of pc-PPSQ with MW = 1400 is ~1.8 Pa*s (at 150 °C in both cases). With an increase in pc-PPSQs molecular weight, the viscosity increases stepwise from ~1.05 * 104 to ~2.9 * 104 Pa*s (both at 150 °C) for pc-PPSQs with MW = 2860 and 3850, respectively. The viscous flow activation energies of pc-PPSQs with MW = 2860 and 3850 are 186 and 195 kJ/mol, respectively.

Multi-benzocyclobutene functionalized siloxane monomers prepared by Piers-Rubinsztajn reaction for low-k materials

Two new multiarmed siloxane monomers of tri-benzocyclobutene monomer namely TriBS and tetra-benzocyclobutene monomer namely TetraBS have been successfully synthesized by Piers-Rubinsztajn (P-R) reaction. After cured at relevant temperature (>200 °C), the monomers converted to transparent highly-crosslinked bulk thermosets. TGA data showed that the crosslinked thermosets exhibited good thermostability with 5% weight loss temperature (Td5) at 451 °C and 518 °C, respectively. According to the results of dynamic mechanical analysis (DMA), the cured TriBS showed glass transition temperature (Tg) at 163 °C, while cured TetraBS showed no Tg under 400 °C. The two materials exhibited good dielectric properties with an average relative permittivity of about 2.42 and 2.54 in a range of frequencies from 100 k to 1 MHz, respectively. The cured TetraBS showed better thermostability, better thermomechanical performance and the cured TriBS showed lower permittivity. Overall, we have prepared low k polymer materials with excellent comprehensive performances such as low k value, extremely low dissipation, good thermostability and high Tg.

Compatibilization of porphyrins for use as high permittivity fillers in low voltage actuating silicone dielectric elastomers.

Polysiloxanes represent, because of their unusual properties, a material with great potential for use in dielectric elastomers (DEs), a promising class of electroactive polymers. Currently, their application as actuators is limited by the need for high driving voltages, as a result of the low relative permittivity possessed by polysiloxanes (∼2–3). Reducing these voltages can be achieved to some degree by using high permittivity additives to improve the permittivity of the polysiloxane. However, modifying such additives so that they are compatible with, and can be dispersed within, polysiloxane elastomers remains challenging. For reliable actuation, full miscibility is key. In this work the porphyrin 5,10,15,20-(tetra-3-methoxyphenyl)porphyrin (TPMP) was investigated as a high permittivity additive. Its behaviour was compared to the analogue that was derivatized with bis(trimethylsiloxy)methylsilane groups using the Piers–Rubinsztajn reaction to improve compatability with silicone formulations. The derivatized porphyrin was dispersed in elastomers and their dielectric and mechanical properties were evaluated. It was discovered that only low levels of incorporation (1–10%) of the siliconized TPMP – much lower than the parent TPMP – were needed to elicit improvements in the permittivity and electromechanical actuation of the elastomers; actuation strains of up to 43% could be achieved using this method.

High-Throughput Synthesis and Characterization of Aryl Silicones by Using the Piers-Rubinsztajn Reaction.

Arylsilicones are widely exploited for their thermal and optical properties. The creation of phenylsilicone elastomers with specific physical properties is typically done by a "one-off" formulation and test process. Herein, it is demonstrated that high-throughput synthesis methods can be used to rapidly prepare a series of arylsilicone elastomers and then the relative impact of different aryl groups on their physical properties is assessed. Aromatic groups were incorporated into polydimethylsiloxane (PDMS) elastomers by exploiting the relative reactivity of different functional groups in the Piers-Rubinsztajn reaction. To analyze trends in the silicone mechanical properties as a function of increasing aryl concentration-structure/property relationships-libraries of elastomers were both quickly synthesized and characterized by using high-throughput suites starting from low viscosity silicone oils/monomers in 96-well plates. Liquid handling parameters were optimized to effectively work with the silicones. Incorporating aryl instead of alkyl crosslinkers into the PDMS backbone increased the silicone elastomer modulus by approximately 50 % (at a crosslink density of 6 %); elastomers prepared with an aromatic crosslinker with three contact points led to much higher moduli compared with those with one contact point at the same crosslink density. When located at precise rather than random points on the silicone chains, diphenylsilicones had lower moduli than analogous monophenylsilicones.

Silicon(II) Cation Cp*Si:+ X–: A New Class of Efficient Catalysts in Organosilicon Chemistry

The catalytic activity of the pentamethylcyclopentadienylsilicon(II) cation Cp*Si:+ was investigated. It was shown that Cp*Si:+ efficiently catalyzes reactions of technical relevance in organosilicon chemistry: Cp*Si:+ proved to be a very efficient nonmetallic catalyst for the hydrosilylation of olefins at low catalyst amounts of <0.01 mol % and for the Piers–Rubinsztajn reaction in order to make controlled silicone topologies. The thermal induction of hydrosilylation which is important for the manufacturing of silicone rubber can be achieved by small amounts of alkoxysilanes.

Formation and application of electrochemically active cross-linked triarylamine–siloxane films using the Piers–Rubinsztajn reaction

Cross-linked triarylamine–siloxane hybrid thin film have been formed using Piers–Rubinsztajn chemistry. Key to this approach was the use of a ring-opening reaction to prevent the evolution of volatile small molecules. A representative cyclic ether containing biphenyl triarylamine compound was synthesized and on ring-opening was shown to form a smooth, glassy, and electroactive films by cross-linking with tetrakis(dimethylsiloxy)silane (QM*4). It was found that the films were electrochemically active with low glass transition temperatures. Cross-linked films were incorporated into organic light emitting diodes (OLEDs) under various conditions and functionality within OLEDs was confirmed. Finally, the resistance of the system to dissolution (orthogonality) was considered by casting F8T2, a p-type emitting polymer, from solution on top of the cross-linked film, which formed a working OLED.

Facile Synthesis of Cx(AB)yCx Triblock Silicone Copolymers Utilizing Moisture Mediated Living‐End Chain Extension

AbstractThe physical and chemical properties of silicone block copolymers depend upon the block size and chemical characteristics. Silicone block copolymer synthetic procedures typically involve chain‐growth polymerization techniques that are difficult to control, require low temperatures, inert atmospheres, etc., and which are subject to polymer chain redistribution; the latter process broadens dispersity and leads to the formation of cyclic monomers that must be removed. Once formed, tuning the size of the individual blocks is challenging. The controlled one‐pot synthesis of organosilicone Cx (AB)y Cx triblock copolymers with aryl rich cores is demonstrated by exploiting the Piers–Rubinsztajn reaction and a hydrolysis/condensation polymerization, both using B(C6F5)3 catalysis. A fast Piers–Rubinsztajn reaction between HSi‐terminated silicones and aryl phenyl ethers leads preferentially to the formation of the aryl‐rich core. Subsequent addition of HSi‐terminated silicones permits controlled chain extension of the flanking homosilicone blocks via a slower hydrolysis/condensation facilitated by atmospheric moisture and leads in one pot, two steps to clean Cx (AB)y Cx triblocks. The products are surprisingly resilient to hydrolysis.