Siloxane Oligomers Research Articles

An alternative approach for compliance testing of food and skin contact silicone elastomers by specific determination of volatile cyclic siloxane oligomers via GC-FID

An alternative approach for compliance testing of food and skin contact silicone elastomers by specific determination of volatile cyclic siloxane oligomers via GC-FID

Polypropylene Crystallinity Reduction through the Synergistic Effects of Cellulose and Silica Formed via Sol-Gel Synthesis.

This study focuses on the development of environmentally sustainable polypropylene (PP)-based composites with the potential for biodegradability by incorporating cellulose and the oligomeric siloxane ES-40. Targeting industrial applications such as fused deposition modeling (FDM) 3D printing, ES-40 was employed as a precursor for the in situ formation of silica particles via hydrolytic polycondensation (HPC). Two HPC approaches were investigated: a preliminary reaction in a mixture of cellulose, ethanol, and water, and a direct reaction within the molten PP matrix. The composites were thoroughly characterized using rotational rheometry, optical microscopy, differential scanning calorimetry, and dynamic mechanical analysis. Both methods resulted in composites with markedly reduced crystallinity and shrinkage compared to neat PP, with the lowest shrinkage observed in blends prepared directly in the extruder. The inclusion of cellulose not only enhances the environmental profile of these composites but also paves the way for the development of PP materials with improved biodegradability, highlighting the potential of this technique for fabricating more amorphous composites from crystalline or semi-crystalline polymers for enhancing the quality and dimensional stability of FDM-printed materials.

Flexible-rigid hybrid siloxane network for stone heritage conservation

Siloxane oligomers produced through the hydrolysis of tri-alkoxysilanes or tetra-alkoxysilanes have been widely used as consolidants for stone heritage. However, the resulting xerogels tend to crack due to the volume shrinkage after curing. In this study, a novel flexible-rigid hybrid siloxane oligomer material is designed by the self-catalyzed copolymerization of di-alkoxysilane (3-Aminopropyl) dimethoxymethylsilane with tetra-alkoxysilane tetraethyl orthosilicate. The flexible linear SiOSi segments produced by di-alkoxysilane are inserted into the tetra-alkoxysilane derived rigid three-dimensional silicon-oxygen domains, as confirmed by spectroscopic characterizations. This unique structure alleviates the shrinkage stress during curing and enables the formation of crack-free xerogels. Therefore, the hybrid siloxane oligomer can invade into the interior of weathered stone to form one three-dimensional continuous network to strengthen its fragile structure. As a result, the flexible-rigid hybrid siloxane oligomer outperforms both as-made polysiloxane consolidant and commercial consolidant for the consolidation of the weathered Tianlong Mountain Grottoes stone samples. The consolidation treatment was evaluated in terms of effectiveness (Leeb hardness, ultrasonic velocity and compressive strength) and compatibility (pore size distribution, water vapor transmission rate and color variation). Following the treatment, the consolidated samples demonstrate remarkable improvements in mechanical properties, reaching a Leeb hardness of 410 HL and a compressive strength of 8.98 Mpa. Additionally, permeability and color variation of the stone after consolidation are all within acceptable ranges. The results confirm the positive consolidation performance of the flexible-rigid hybrid siloxane oligomer on weathered Tianlong Mountain Grottoes stone, indicating promising practical applications.

Experimental and theoretical study on the thermal stability and pyrolysis mechanism of octamethyltrisiloxane (MDM) with lubricating oil

In actual organic Rankine cycle systems (ORCs), the inclusion of lubricating oil in the working fluid is nearly unavoidable. Under the condition of high-temperature operation, the presence of lubricating oil can potentially exacerbate the thermal stability of the working fluid. The impact of polyol ester (POE) and mineral lubricant on the thermal stability of octadethyltrisiloxane (MDM) is studied. Results indicate that both POE and mineral lubricant contribute to the decomposition of MDM to a certain extent. Specifically, at a 5.0% mass fraction of POE and mineral lubricant, MDM remains its stable at 230 °C and 210 ℃, respectively. However, as the mass fraction of lubricant increases, the decomposition of MDM intensifies, with mineral lubricant exhibiting a more pronounced effect compared to POE lubricant. Regarding pyrolysis products, the presence of lubricants leads to an increase in CH4, C2H6 and C2H4 gases. Furthermore, the addition of lubricant promotes the formation of siloxane oligomers, particularly MD5M to MD9M, and enhances the production of unidentified products. Compared to MDM, both POE and mineral lubricant molecules exhibit lower bond dissociation Gibbs free energies. The free radicals generated from lubricant decomposition are prone to hydrogen abstraction reactions with MDM to promote MDM decomposition. Moreover, ReaxFF simulation results demonstrate that lubricant molecules also enhanced the activation of MDM and increased its susceptibility to Si-C bond cleavage. Following the removal of the methyl group, the Si-O bonds in the radicals are more likely to break, leading to the formation of additional siloxane oligomers through Si-O bond recombination. Kinetic analysis reveals that the apparent activation energy of MDM decomposition drops from 134.4 kJ∙mol−1 to 110.8 kJ∙mol−1 as the mass fraction of n-hexadecane (model compounds for mineral lubricant) rises from 0% to 10.30%.

Emulsion template – based porous silicones with piezocapacitive response

Porous silicones were prepared by thiol-ene photoaddition or hydrolysis - condensation cross-linking in emulsion template in the presence of a pyridyl-modified siloxane oligomer as surfactant, at room temperature. Hexamethyldisiloxane (HMDS) was tested as alternative, more eco-friendly solvent in competition with toluene. Variations in the composition of silicone precursors, thus in cross-linking density and method, allowed tuning of mechanical properties. The piezocapacitive response of the porous silicones was investigated, focusing on the dielectric material as potential sensing element in capacitive pressure sensors. The capacitance variation showed linearity on wide pressure domains, roughly between 2 and 300 kPa, depending on the mechanical properties of the porous monoliths. A direct correlation between sensitivity and Young's modulus was found, which allows tuning of the sensing behavior. The softest material, prepared with a binary mixture of silicone precursors, exhibited a sensitivity of 8.7 × 10−3 kPa−1 on 9–29 kPa pressure range. A porous silicone – MWCNT composite showed spectacular increase in sensitivity, with maximum value of 0.747 kPa−1 and 0–7.5 kPa sensing range when compressed at 30%. Gauge factors of 29.2 in the compressive strain range of 13–30% and as high as 88.8 in the compressive strain range of 25–50% were found.

Preparation of thermal interface materials with high thermal conductivity through the synergistic effect of Monoalkoxy-Terminated polysiloxane and branched siloxane oligomers

Four mono-alkoxysilyl-terminated asymmetric siloxane oligomers and a dimethylvinylsilyl-terminated branched-chain structure siloxane oligomer were prepared by a series of reactions to improve the filling loads and dispersion of Al2O3 particles in the polysiloxane matrix. Their influence on the surface modification of Al2O3 particles and the viscosity of composite materials was investigated. When the branched-chain siloxane oligomer was not used, mono-trimethoxysilyl-terminated asymmetric siloxane oligomers exhibited the best modification effect on the Al2O3 surface, and the silicone paste prepared by filling 70.8 vol% mixed-size Al2O3 particles had the lowest viscosity. When the branched-chain siloxane oligomer was used, the filling load of the modified Al2O3 particles could be further increased to 84.3 vol% under the synergistic effect of the mono-trimethoxysilyl-terminated asymmetric siloxane oligomers and the branched-chain siloxane oligomer. The viscosity of the silicone paste decreased with the increase in the polymerization degree of the dimethylsiloxane segment in the-mono trimethoxysilyl-terminated asymmetric siloxane oligomers. Meanwhile, the thermal conductivity of these silicone pastes also exhibited an increasing trend with the increase in the polymerization degree of the asymmetric siloxane oligomers. A thermal interface material with a thermal conductivity higher than 8.0 W/(m·K) was successfully prepared by using the asymmetric siloxane oligomers as the surface modification agent for Al2O3 particles and the branched-chain siloxane oligomer as the fluidity modifier for silicone paste.

Ferrocene functionalized oligomeric siloxane building blocks as potential linkers for biological active molecules

Despite the fact, that biologically active molecules (e.g., antioxidants, antibiotics and antiviral reagents) were investigated intensively in the last decades, new linker molecules and building blocks, which can enhance the activity and change the polarity of compounds is still a growing field in pharmaceutic research. The application of a ferrocene moiety in combination with a siloxane linker attached to a biological active molecule is realized in the present study for the first time. A method is introduced that uses mono- (FcLi) and dilithioferrocene (FcLi2) to perform anionic ring opening reactions of hexamethylcyclotrisiloxane (D3). The formation of lithium silanolate species αDnLi (α = Fc, D3 = (SiMe2O)3) was observed, followed by the termination of the ring opening reactions with chlorosilanes Cl–ω to obtain siloxane oligomers of type αDnω. Approaches were investigated to enable ω = SiMe2H and ω = SiMe2Cl functionality. It was shown, that oligomeric siloxanes were able to undergo further hydrosilylation reactions with the introduction of a phenol moiety.

The Preparation of Acryloxyl Group Functionalized Siloxane Polymers and the Study of Their Ultra Violet Curing Properties.

Polysiloxane with multiple acryloxyl groups at the terminal site of the polymer chain was synthesized by the condensation reaction between hydroxyl-terminated polysiloxane and acryloyl chloride and used to improve the cross-linking density of UV-curable silicone materials initiated from dual acryloxy-terminated symmetric polysiloxane or single acryloxy-terminated asymmetric polysiloxane with the mixture of Irgacure 1173 and Irgacure 184 at a mass ratio of 1:1 as the photoinitiator. The effects of factors such as initiator composition, UV irradiation time, structure, and molecular weight of linear dual acryloxy-terminated or single acryloxy-terminated asymmetric siloxane oligomers on the gelation yield, thermal properties, water absorption, and water contact angle of UV-cured film were investigated. The synthesized cross-linking density modifier can be copolymerized with acryloxy-functionalized linear polysiloxanes under the action of a photoinitiator to increase the cross-link density of UV-cured products effectively. Both linear dual acryloxy-terminated or single acryloxy-terminated asymmetric siloxane oligomers can be copolymerized with cross-link density modifiers within 20 s of UV irradiation. The gelation yields of the UV-cured products obtained from the dual acryloxy-terminated siloxane oligomers were greater than 85%, and their surface water contact angles increased from 72.8° to 95.9° as the molecular weight of the oligomers increased. The gelation yields of UV-cured products obtained from single acryloxy-terminated asymmetric siloxane oligomers were less than 80%, and their thermal stabilities were inferior to those obtained from the dual acryloxy-terminated siloxane oligomers. However, the water contact angles of UV-cured products obtained from these single acryloxy-terminated asymmetric siloxane oligomers were all greater than 90°.

Engineering circularly polarized light emission in nanostructured oligodimethylsiloxane-helicene chiral materials.

Chiroptical properties in the bulk state can be tuned by controlling the formation of chiral ordered nanostructures. Here, we present a series of discrete oligodimethylsiloxane-helicene-pyrene block molecules with varying oDMS lengths and study the nanostructures formed in both bulk and solution, including their chiroptical properties. In bulk, ordered 2D nanostructures self-assemble, driven by phase segregation induced by the siloxane oligomers, with clear differences in the properties of the racemic and enantiopure versions. Moreover, intermolecular pyrene interactions lead to excimer emission. As a result, up to a 5-fold increase in circularly polarized luminescence is observed in the solid state as compared to the solution, accompanied by a clear influence of the pyrene excimer emission on the overall emission process. Interestingly, in the ordered lamellar packing achieved from long oDMS units, the excimer emission shows very little net circular polarization, while in the disordered state achieved from shorter oDMS units, this excimer emission displays a significant degree of circular polarization. These results demonstrate that functionalizing chiroptical building blocks with discrete oligodimethylsiloxane chains is a versatile strategy to control photophysical properties and modulate chiroptical emission in bulk. This approach advances the integration of chiroptical materials into devices, enabling diverse applications ranging from optoelectronics to communication technologies.

Direct cross-linking of silyl-functionalized cage siloxanes via nonhydrolytic siloxane bond formation for preparing nanoporous materials.

Bottom-up synthesis of siloxane-based nanoporous materials from siloxane oligomers is promising for constructing well-defined structures at a molecular level. Herein, we report the synthesis of nanoporous materials consisting of cage-type siloxanes through the nonhydrolytic siloxane bond formation reaction. Cage siloxanes with double-n-ring geometries (n = 4 or 6) modified with dimethylsilyl and dimethylethoxysilyl groups are synthesized and directly cross-linked using a B(C6F5)3 catalyst, resulting in the formation of porous networks composed of alternating cage siloxane nodes and tetramethyldisiloxane (-SiMe2OSiMe2-) linkers. Compared with conventional hydrolysis and polycondensation reactions of alkoxysilyl-modified cage siloxanes under acid conditions, the non-hydrolytic condensation reaction was found favorable for the formation of porous siloxane networks without unwanted cleavage of the siloxane bonds.

Reactions of (mesityl)n(methyl)2-nsilylene complexes with pyridine-N-oxide (n = 1 and 0): formation of silanone complexes and a disiloxanyloxy complex.

Silanones (OSiR2), a heavier congener of ketones (R2CO), are highly reactive species that are readily converted to oligomeric siloxane (O-SiR2)n. Coordination of silanones to the transition-metal fragments to afford silanone-coordinated complexes is a reliable silanone stabilization method. Recently, our group reported the synthesis, structures, and reactivity of dimesityl-substituted silanone complexes Cp*(OC)2M{OSiMes2(L)}(SiMe3) (M = W, Mo, L: Lewis base, Cp*: η5-C5Me5, Mes: 2,4,6-Me3C6H2). Herein, to investigate the effect of substituents on the silicon atom during the formation of a silanone complex, we demonstrated the use of Mes and smaller Me groups. As a result, the formation of Mes(Me)-substituted silanone molybdenum complex Cp*(OC)2Mo{OSiMes(Me)(py)}(SiMe3) (5b, py: pyridine) was suggested, the silanone tungsten complex Cp*(OC)2W{OSiMes(Me)(DMAP)}(SiMe3) (4a, DMAP: 4-(dimethylamino)pyridine) was obtained, and a dimethyl-substituted disiloxanyloxy(dioxo) complex Cp*(O)2W(OSiMe2OSiMe3) (9) was formed. The reaction of 4a with PMe3 proceeded via the elimination of DMAP and migration of the SiMe3 group to the oxygen atom of the silanone ligand to afford Cp*(OC)2W(SiMes(Me)OSiMe3)(PMe3) (11a). The Mo complex Cp*(OC)2Mo(SiMes(Me)OSiMe3)(PMe3) (11b) was produced by the reaction of Cp*(OC)2Mo{SiMes(Me)}(SiMe3) (7b) with pyridine-N-oxide in the presence of PMe3.

Mechanochemical Interaction of Phenylboronic Acid with Polyphenylsilsesquioxane and a Hydroxy(phenyl)siloxane Oligomer

The interaction of phenylboronic acid with polyphenylsiloxane and a hydroxy(phenyl)siloxane oligomer has been studied. For the first time, phenylboronic acid was used as a starting material for the production of polyboronphenylsiloxanes under conditions of mechanochemical activation. It has been established that the main side processes induced by activation are abstraction of the phenyl substituent from the boron atom, formation of biphenyl, and trimerization of phenylboronic acid. Since boron compounds (including phenylboronic acid) have biological activity, their introduction into the polymer chain will make it possible to obtain materials with useful properties. For example, boron-containing polymers can be used as coatings to protect against insect vectors of various diseases. The work is fundamental in nature and contributes to revealing and understanding the mechanisms of mechanochemical modification of organosilicon polymers.

Thermal stability and thermal decomposition mechanism of octamethyltrisiloxane (MDM): Combined experiment, ReaxFF-MD and DFT study

The thermal stability and decomposition mechanism of octamethyltrisiloxane (MDM) were studied using a combination of experimental, ReaxFF simulation, and DFT calculation techniques. After heating MDM for 24 h at 250 °C and 1 MPa, the signature product CH4 was detected, along with liquid products such as hexamethyldisiloxane (MM) and decamethyltetrasiloxane (MD2M). The decomposition rate of MDM remained relatively constant in the temperature range of 250 °C–320 °C but exhibited a sharp increase at 350 °C. Higher pressure was found to promote MDM polymerization. The oxygen (O) atoms displayed a large negative electrostatic potential, while the hydrogen (H) and silicon (Si) atoms exhibited a large positive potential. The electrostatic interaction facilitated the rearrangement reactions, with O and carbon (C) atoms being the most reactive for electrophilic and free radical reactions. The thermal decomposition of MDM initiated with the cleavage of Si–C bonds. Hydrogen extraction reactions between methyl radicals and MDM, as well as Si–O bond rearrangement reactions of demethylated radicals with MDM, further promoted MDM decomposition and the formation of CH4 and siloxane oligomers. These findings are significant for the safe application of MDM as a working fluid in ORC system.

Mechanochemical Interaction of Phenylboronic Acid with Polyphenylsilsesquioxane and a Hydroxy(phenyl)siloxane Oligomer

Mechanochemical Interaction of Phenylboronic Acid with Polyphenylsilsesquioxane and a Hydroxy(phenyl)siloxane Oligomer

Dimethylsilanediol from silicone elastomers: Analysis, release from biopharmaceutical process equipment, and clearance studies

Polysiloxanes are considered one of the most important commercial families of synthetic elastomers. They are frequently employed in biopharmaceutical manufacturing equipment as flexible single-use solutions due to superior material properties and compatibility with diverse sterilization methods. Extractables and leachables (E&L) testing is essential in qualifying such equipment, involving extraction studies to assess the potential release of compounds from plastic components for risk assessment. Silicone releases oligomeric siloxanes and small hydrolysis products, with dimethylsilanediol (DMSD) being the main hydrolysis product found in significant concentrations in aqueous process solutions. DMSD presents challenges for analysis, requiring specifically tailored analytical methods to detect it, which are commonly not applied in standard E&L screening tests. In biopharmaceutical manufacturing, it is relevant to consider the potential of DMSD to repolymerize into silicone oil when specific process parameters are altered. This may lead to interactions with drug ingredients, including proteins, resulting in the formation of aggregates. We synthesized and characterized DMSD using X-ray structure analysis and established an HPLC method with a refractive index detector to investigate the release of DMSD from commercially available silicone tubing used in drug manufacturing following autoclaving and irradiation. Subsequently, we assessed typical biopharmaceutical downstream operations for effectively removing this compound from the process stream.

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

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.

Synthesis and Characterization of Novel Phenolic Resin/Siloxane Aerogels via Ambient Pressure Drying

Novel phenolic resin/silicone aerogels (PR-Si) were prepared through a facile sol-gel polymerization and ambient pressure drying process without solvent exchange. Without the addition of an additional catalyst, the hydroxyl condensation reaction between the siloxane oligomer and the phenolic resin resulted in the silicon being incorporated into the PR. The obtained aerogels exhibited high compressive strength (0.84–21.11 MPa) and low thermal conductivities [0.046–0.077 W/(m·K)]. The introduction of a Si–O network structure in the PR effectively improved the mechanical properties and thermal stability of aerogels. It is clear from the TGA plot that the mass loss temperature of the PR-Si aerogel was increased by 73 and 79 °C for the weight loss temperatures of 5 and 10% compared to cured pure PR.

РАЗРАБОТКА И ПОИСК ФУНКЦИОНАЛЬНОСТЕЙ НОВЫХ ОРГАНОКРЕМНЕЗЕМНЫХ ГИБРИДНЫХ НАНОКОМПОЗИТОВ С ВКЛЮЧЕНИЕМ БИОПОЛИМЕРОВ ХИТОЗАНА В СИЛОКСАНОВУЮ ОСНОВУ ПРИ ИХ ПРЕОБРАЗОВАНИИ В МОНОДИСПЕРСНЫЕ ЧАСТИЦЫ МЕЗОПОРИСТОГО КРЕМНЕЗЕМА

A new universal approach to the biomimetic synthesis of hybrid organosilicate nanocomposites with texture and functionality good control has been developed, which consists in the use of biomacromolecules as mesogenic templates. The main strategy is to combine the self-association of polysaccharide nanorods with the flexibility of the sol-gel process in the chemistry of siloxane oligomers formed at various pH values of 3, 5, 8. The measured isotherms of low-temperature nitrogen adsorption-desorption by samples obtained at pH 5 and 8 refer to isotherms of type IV (a) characteristic of mesoporous adsorbents. The isotherms are dominated by the triangular hysteresis H2(a), which is due to network effects in ordered mesoporous materials of the SBA-16 and KIT-5 types. The isotherms of the samples obtained at pH 3 are of the hybrid type (I+IV) with the H4 hysteresis inherent in microporous adsorbents with slit-like mesopores between agglomerates of silica particles. It is shown that the control of the textural properties of hybrid nanocomposites and porous silica is possible by changing the temperature of thermal activation of organosilicate samples and the pH value of the silica gel precipitation medium. The advantage of the developed synthesis is the formation of new functionalities on the surface of silica through its heat treatment while maintaining the polysaccharide template either as its own functional basis or as a carbon resource.

Synthesis of a siloxane oligomer containing methyl acryloxy group for promoting the adhesion of addition-type silicone rubber to copper plate

An adhesion promoter containing methyl acryloxy group was synthesized according to a non-hydrolysis sol-gel method with methyl phenyl silicone oil containing hydroxyl terminal group, methyl vinyl dimethoxy silane, and γ–methyl acryloxy propyl methyl dimethoxy silane (KH572) as raw materials and then applied in an addition-type silicone rubber. The structure of the product was characterized by Fourier transform infrared spectroscopy (FT-IR) and nuclear magnetic resonance hydrogen spectrum (1H NMR). In addition, scanning electron microscope (SEM), mechanical testing machine and video-based optical contact angle measuring instrument were used to test its performance. We found that the adhesion promoter largely improved the bonding performance of the addition-type silicone rubber and showed the better compatibility with liquid silicone resins. When the amount of the adhesion promoter was 2.0 phr, the shear strength between silicone rubber and copper plate reached 1.33 MPa. The optical performance test results indicated that the light transmittance of silicone rubber was slightly changed when the addition amount of the adhesion promoter was no more than 2.0 phr, and this met the encapsulation requirements of electronic packaging adhesives. The contact angle test results indicated that the adhesion promoter reduced the static contact angle between the liquid silicone rubber and copper plate surface and improved the wettability. In addition, oxidation experiments, thermal resistance experiments, SEM tests and XPS surface analysis preliminarily proved that the adhesion promoter could significantly enhance the adhesion via chemical bonds formed with both the cured silicone rubber and the surface of copper plate substrate.

Synthesis of a siloxane oligomer containing ether bond for promoting the adhesion between addition-cure silicone rubber and polycarbonate (PC)

Synthesis of a siloxane oligomer containing ether bond for promoting the adhesion between addition-cure silicone rubber and polycarbonate (PC)