Siloxane Oligomers Research Articles

Synthesis and structure evolution of phenolic resin/silicone hybrid composites with improved thermal stability

Phenolic resin/silicone hybrid composites (MPR) were prepared by a facile and low-cost method. FTIR results show that polycondensation of siloxane occurs in the presence of catalyst and water in the system, and siloxane oligomer was formed. During the curing process, the transesterification reaction between siloxane oligomer and phenolic resin (PR) makes silicon incorporated into PR. The TGA results indicate that introducing Si–O structure into PR can effectively improve the thermal stability of the resin. Compared with cured neat PR, temperatures at 5 and 10% mass loss of cured MPR can be improved by 43 and 36 °C. Its char yield at 800 °C was increased by about 9.1%. Cured MPR has been characterized by FTIR, XPS, XRD and Raman spectra to discuss the chemical state changes of silicon during pyrolysis process, as well as the effect of silicon on the char yield. On the one hand, the formation of Si–O–C structure can reduce the number of phenyl hydroxyl groups, which contributes to the reduced weight loss. On the other hand, the results indicate that Si–Ox structure was formed from the oxidation of Si–CH3 and hydrolysis of Si–O–C structures. According to Raman analyses, introducing silicone into the system cannot help to promote the formation of a more ordered structure. Additionally, the mechanical properties of cured MPR have also been improved.

Acidic pH weakens the bonding effectiveness of silane contained in universal adhesives

ObjectivesSome silane-containing universal adhesives were introduced that a separate ceramic primer was unnecessary to glass-ceramic bonding because of incorporated silane. We aimed to investigate the effectiveness of silane in universal adhesives with acidic media. MethodsA functional γ-methacryloxypropyltrimethoxysilane (γ-MPTS) was used, and its pH value was adjusted to 2.7 by adding hydrochloric acid (HCl) or 10-methacryloxydecyl phosphate (MDP). The prepared acidic silane solutions after 2h or 10d storage were characterized by Fourier transform infrared spectroscopy (FTIR), 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. Micro-shear bond strength (μSBS) was used to evaluate the bonding performance of glass ceramics. Two silane-containing and two silane-free universal adhesives were included. Field-emission scanning electron microscopy fractography analysis was also performed. ResultsFTIR, 1H and 13C NMR revealed that the hydrolysis of γ-MPTS and the self-condensation reaction of silanol groups occurred over time under acidic conditions (HCl or MDP solution). This reaction formed the siloxane oligomers. For glass-ceramic bonding, the μSBS of acidic silane after 10 d storage was lower than that of silane stored for 2h storage (p<0.05), although the difference among the μSBS of the four universal adhesives were nonsignificant (p>0.05). Additionally, cohesive failure was the main fracture pattern of universal adhesive bonding. SignificanceThe effectiveness of silane contained in low pH universal adhesives can be weakened by dehydration self-condensation and consequently became unstable. For the enhancement of glass-ceramic bonding efficiency with universal adhesives, a separate ceramic primer was recommended.

Functional siloxanes with photo-activated, simultaneous chain extension and crosslinking for lithography-based 3D printing

A novel, poly(dimethyl siloxane)-based photopolymer that exhibits simultaneous linear chain extension and crosslinking was suitable for vat photopolymerization additive manufacturing. Photopolymer compositions consisted of dithiol and diacrylate functional poly(dimethyl siloxane) oligomers, where simultaneous thiol-ene coupling and free radical polymerization provided for linear chain extension and crosslinking, respectively. Compositions possessed low viscosity before printing and the modulus and tensile strain at break of a photocured, higher molecular weight precursor after printing. Photorheology and soxhlet extraction demonstrated highly efficient photocuring, revealing a calculated molecular weight between crosslinks of 12,600 g/mol and gel fractions in excess of 90% while employing significantly lower molecular weight precursors (i.e. < 5300 g/mol). These photocured objects demonstrated a 2× increase in tensile strain at break as compared to a photocured 5300 g/mol PDMS diacrylamide alone. These results are broadly applicable to the advanced manufacturing of objects requiring high elongation at break.

Influence of Solvent Swelling on Ultrafast Structural Dynamics in Polydimethylsiloxane Thin Films by Two-Dimensional IR Spectroscopy.

Fourier transform infrared and two-dimensional IR (2D-IR) spectroscopies were applied to polydimethylsiloxane (PDMS) cross-linked elastomer and a siloxane oligomer without solvent and swollen or dissolved in various solvents. The silicon hydride, which is covalently bound to the polymer chains, was the vibrational probe for the systems studied. There is almost an absence of vibrational solvatochromism in these systems. Frequency-frequency correlation functions obtained by 2D-IR spectroscopy show that the insensitivity of the FTIR spectra is due to overwhelming heterogeneity. However, the homogeneous contribution to the FTIR spectrum is smaller for the elastomer than the oligomer showing that the cross-linking process restricts the frequency fluctuations that are experienced by the hydride mode. The silicon hydride mode in a cross-linked, solvent-free PDMS film also exhibits spectral diffusion that must be due to polymer structural motions on the ultrafast time scale that are active above the glass transition temperature. Once solvents penetrate and swell the elastomer, the polymer likely continues to experience these polymer structural motions. However, we find that the vibrational dynamics are characteristic of the infiltrating solvents, showing that at least some fraction of the measured dynamics originate in solvent motions.

Preparation of irrefrangible polyacrylamide hybrid hydrogels using water-dispersible cyclotetrasiloxane or polyhedral oligomeric silsesquioxane containing polymerizable groups as cross-linkers

Irrefrangible polyacrylamide hybrid hydrogels were prepared using polymerizable siloxane oligomers as cross-linkers (CyTS-MNaandPOSS-MNa, respectively).

High Efficiency (&gt;17%) Si‐Organic Hybrid Solar Cells by Simultaneous Structural, Electrical, and Interfacial Engineering via Low‐Temperature Processes

AbstractHighly efficient organic–inorganic hybrid solar cells of Si‐poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) have been demonstrated by simultaneous structural, electrical, and interfacial engineering with low processing temperature. Si substrate has been sculpted into hierarchical structure to reduce light reflection loss and increase interfacial junction area at the same time. Regarding the electrical optimization, highly conductive organic PEDOT:PSS layer has been formulated with low sheet resistance. It is argued that the sheet resistance, rather than conductivity, is the primary parameter for the high efficiency hybrid cells, which leads to the optimization of thickness, i.e., thick enough to have low sheet resistance but transparent enough to pass the incident sunlight. Finally, siloxane oligomers have been inserted into top/bottom interfaces by contact‐printing at room ambient, which suppresses carrier recombination at interfaces and reduces contact resistance at bottom electrode. Contrary to high‐temperature doping (for the formation of front surface or back surface fields), wet solution processes or vacuum‐based deposition, the contact‐printing can be done at room ambient to reduce carrier recombination at the interfaces. The high efficiency obtained with low processing temperature can make this type of cells be a possible candidate for post‐Si photovoltaics.

Photoswitchable Nanomaterials Based on Hierarchically Organized Siloxane Oligomers

AbstractMaterials with highly ordered molecular arrangements have the capacity to display unique properties derived from their nanoscale structure. Here, the synthesis and characterization of azobenzene (AZO)‐functionalized siloxane oligomers of discrete length that form photoswitchable supramolecular materials are described. Specifically, synergy between phase segregation and azobenzene crystallization leads to the self‐assembly of an exfoliated 2D crystal that becomes isotropic upon photoisomerization with UV light. Consequently, the material undergoes a rapid athermal solid‐to‐liquid transition which can be reversed using blue light due to the unexpectedly fast 2D crystallization that is facilitated by phase segregation. In contrast, enabling telechelic supramolecular polymerization through hydrogen bonding inhibits azobenzene crystallization, and nanostructured pastes with well‐ordered morphologies are obtained based on phase segregation alone, thus demonstrating block copolymer‐like behavior. Therefore, by tailoring the balance of self‐assembly forces in the azobenzene‐functionalized siloxane oligomers, fast and reversible phase‐changing materials can be engineered with various mechanical properties for applications in photolithography or switchable adhesion to lubricant properties.

Amino Siloxane Oligomer Modified Graphene Oxide Composite for the Efficient Capture of U(VI) and Eu(III) from Aqueous Solution

Poly 3-aminopropyltriethoxysilane is a highly reactive high-molecular polymer because of the existence of abundant amino groups, which presents a strong affinity toward different metal cations. In view of this, the novel poly amino siloxane oligomer modified graphene oxide composite (PAS–GO) was fabricated by a facile cross-linking reaction and applied to capture U(VI)/Eu(III) ions from aqueous solution. The interaction mechanisms between the PAS–GO and U(VI)/Eu(III) were elaborated. The modification by NH2 increased the sorption sites and improved the sorption capacities because of the synergistic effect of chelation with U(VI)/Eu(III). X-ray photoelectron spectroscopy revealed that nitrogen groups are involved in the removal of U(VI)/Eu(III) since nitrogen atoms of amine groups provided the lone pair of electrons with U(VI)/Eu(III) species. The maximum sorption capacity of U(VI) and Eu(III) on the PAS–GO at 298 K calculated by the Langmuir isotherm model was 310.63 and 243.90 mg/g, respectively. The PAS...

Protecting and Leaving Functions of Trimethylsilyl Groups in Trimethylsilylated Silicates for the Synthesis of Alkoxysiloxane Oligomers

AbstractThe concept of protecting groups and leaving groups in organic synthesis was applied to the synthesis of siloxane‐based molecules. Alkoxy‐functionalized siloxane oligomers composed of SiO4, RSiO3, or R2SiO2 units were chosen as targets (R: functional groups, such as Me and Ph). Herein we describe a novel synthesis of alkoxysiloxane oligomers based on the substitution reaction of trimethylsilyl (TMS) groups with alkoxysilyl groups. Oligosiloxanes possessing TMS groups were reacted with alkoxychlorosilane in the presence of BiCl3 as a catalyst. TMS groups were substituted with alkoxysilyl groups, leading to the synthesis of alkoxysiloxane oligomers. Siloxane oligomers composed of RSiO3 and R2SiO2 units were synthesized more efficiently than those composed of SiO4 units, suggesting that the steric hindrance around the TMS groups of the oligosiloxanes makes a difference in the degree of substitution. This reaction uses TMS groups as both protecting and leaving groups for SiOH/SiO− groups.

Protecting and Leaving Functions of Trimethylsilyl Groups in Trimethylsilylated Silicates for the Synthesis of Alkoxysiloxane Oligomers.

The concept of protecting groups and leaving groups in organic synthesis was applied to the synthesis of siloxane-based molecules. Alkoxy-functionalized siloxane oligomers composed of SiO4 , RSiO3 , or R2 SiO2 units were chosen as targets (R: functional groups, such as Me and Ph). Herein we describe a novel synthesis of alkoxysiloxane oligomers based on the substitution reaction of trimethylsilyl (TMS) groups with alkoxysilyl groups. Oligosiloxanes possessing TMS groups were reacted with alkoxychlorosilane in the presence of BiCl3 as a catalyst. TMS groups were substituted with alkoxysilyl groups, leading to the synthesis of alkoxysiloxane oligomers. Siloxane oligomers composed of RSiO3 and R2 SiO2 units were synthesized more efficiently than those composed of SiO4 units, suggesting that the steric hindrance around the TMS groups of the oligosiloxanes makes a difference in the degree of substitution. This reaction uses TMS groups as both protecting and leaving groups for SiOH/SiO- groups.

Poly(imide-siloxane)s based on hyperbranched polyimides

AbstractPoly(imide-siloxane)s differing in their composition were prepared and characterized. The starting polymer (control) was the hyperbranched polyimide based on 4,4′-oxydiphthalic anhydride and 4,4′,4″-triaminotriphenylmethane. In the poly(imide-siloxane)s, 10 or 40–50 mol% of the 4,4′,4″-triaminotriphenylmethane was theoretically substituted for by amine-terminated siloxane dimer or oligomers. 1,3-Bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, bis(3-aminopropyl)-terminated poly(dimethylsiloxane) with a theoretical number-average molar mass of 1000 g·mol−1 and bis(3-aminopropyl)-terminated poly(dimethylsiloxane) with a theoretical number-average molar mass of 2500 g·mol−1 were used for this purpose. The thermo-mechanical properties and gas separation characteristics for hydrogen, carbon dioxide and methane of these polymeric products were shown to be dependent on their composition.

Modification of water transport properties of porous building stones caused by polymerization of silicon-based consolidation products

Abstract This work studies the polymerization process of four different commercially available silicon-based polymers and their consequent effect on surface tension and water transport properties of natural stones used in architectural monuments, essential for modeling and predicting the durability of natural stones against weathering action of aqueous solutions. The four products studied consisted of two ethyl-silicate based materials, an alkyl-alkoxy siloxane oligomer with hydrophobic agents and finally, a silane/siloxane emulsion. In all cases, the morphology of the amorphous material deposited into the pore network of stones was examined by electron microscopy (SEM). The polymerization process was studied by infrared spectroscopy (FTIR) on both inert surface and porous stone substrate. The treated stone specimens were further tested after polymerization in terms of determination and comparison of water absorption coefficient, open porosity, pore size distribution (mercury intrusion porosimetry) and surface tension (contact angle measurements) properties. According to the analysis, the modification of the wetting properties of the stone surface should be related rather with the chemistry than the microstructure of the xerogels alone.

Performance of white light emitting diodes prepared by casting wavelength‐converting polymer on InGaN devices

ABSTRACTUV‐curable siloxane oligomers prepared by a hydrosilylation reaction were used as encapsulant. Two fluorescent copolymers with emission covering the range of green and red light were synthesized and blended with the UV‐curable siloxane oligomers and photoinitiator to make the wavelength‐converting polymer (WCP). WCP was casted on blue light emitting InGaN diodes and UV cured to fabricate white light emitting diodes (WLEDs). Effects of monomer compositions on the fluidity of uncured oligomer, together with the optical, thermal, and mechanical properties of the cured polysiloxane were studied. We also investigated the influence of red fluorescent polymer which was comprised of repeating units of dioctylfluorene, bisthienyl‐benzothiadiazole, and benzothiadiazole segments on the color rendering index, correlated color temperature, and luminous efficacy of WLED. Because of the good match between the absorption and emission features of the segments in the fluorescent copolymers, white LEDs can be produced by fluorescent copolymer blends which can support incomplete energy transfer. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45210.

One pot synthesis of carboxyl functionalized-polyhedral oligomeric siloxane based monolith via photoinitiated thiol-methacrylate polymerization for nano-hydrophilic interaction chromatography

A hybrid monolith exhibiting almost retention independent separation performance in hydrophilic interaction chromatography (HILIC) was obtained by one-pot photoinitiated thiol-methacrylate polymerization. Polyhedral oligomeric silsesquioxane containing methacrylate units (POSS-MA) was used as the main monomer and crosslinking agent, together with a hydrophilic ligand with two carboxyl groups, mercaptosuccinic acid (MSA) as the thiol agent and chromatographic ligand. The isocratic separation of nucleosides, nucleotides and organic acids on MSA attached-poly(POSS-MA) monolith was investigated in HILIC mode. The van-Deemter plots for obtained for nucleosides, nucleotides and benzoic acids clearly showed that there were two regions in each graph with two different slopes in the studied range of linear flow rate (i.e. 0.2–4.3mm/s). The slope of plate height-linear velocity curve was so small in the low linear velocity region between 0.2–2.1mm/s while the slope in high linear velocity region between 2.1–4.3mm/s was so higher with respect to the first region. The van-Deemter plots sketched for all analyte grous used in HILIC mode obeyed this tendency Almost “retention independent plate height behavior” was demonstrated in HILIC, using nucleotides, nucleotides or benzoic acids as the analytes in the linear velocity range of 0.2–2.1mm/s. This behavior was explained by the porous structure of the synthesized monolith facilitating the convective transport of analytes. The variation of plate height was not retention-independent within high linear velocity range (>3.2mm/s) when nucleosides were separated in HILIC mode.

Facile Preparation of Photocurable Siloxane Composite for 3D Printing

This study presents the development and successful 3D printing of siloxane composite. Complex structures are 3D printed using vector‐scanning stereolithography apparatus. Siloxane oligomer and a commercial resin in the presence of an appropriate photoinitiator combine to form a hybrid material that photopolymerizes when exposed to UV laser at 405 nm wavelength. Measurements with differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, universal testing machine (UTM), and material testing system (MTS) reveal various properties of methacrylate resin filled with different concentrations of siloxane. Fourier transform infrared and Raman spectroscopy results reveal molecular structural change due to chemical reaction with the siloxane introduction. Atomic force microscopy imaging displays the surface morphology characteristics of the hybrid polymer while the contact angle confirms the surface energy existing on the samples. The 3D‐printed structures show unique physicochemical and thermomechanical properties that can lead to great potential for new applications in the field. This work is the first comprehensive study on 3D printing using siloxane through stereolithography. image

PeakForce QNM AFM study of chitin-silica hybrid films

Chitin-silica hybrid thin films, prepared through the colloidal self-assembly of chitin nanorods and siloxane oligomers, have been studied for the first time by PeakForce QNM AFM mode to explore their structure and mechanical behaviour. The change in structure and mechanical properties of chitin-silica hybrids is mainly driven by the relative quantities in chitin nanorods and silica, expressed as the chitin volume fraction ϕchi. The coating of the chitin polysaccharide by silica leads to an increase of the nanorods diameter and films surface roughness at small ϕchi values. The DMT (Derjaguin-Muller-Toporov) modulus increased both at small ϕchi due to a large amount of silica and at very high ϕchi→1 due to an incomplete tip penetration between nanorods. The local parallel orientation of nanorods observed at different ϕchi values resulted in a modulus increase due to an enhancement of the cohesion between nanorods.

Adsorption of vinyl trimethoxysilane and formation of vinyl siloxane nanolayers on zinc surface from aqueous solution

The method of quartz crystal microbalance is used to study adsorption of vinyl trimethoxysilane (VS) on the surface of zinc from an aqueous solution. Adsorption isotherms are obtained. Approaches corresponding to the known adsorption isotherms are used for interpretation of adsorption data: Langmuir, BET, Flory–Huggins, Langmuir multicenter, Temkin, and Langmuir–Freundlich. It is shown that silanes are adsorbed on the surface of thermally deposited zinc from aqueous solutions and displace adsorbed water from the surface by occupying more than six adsorption sites on the surface. It is found that monolayer coverage of the zinc surface is reached at a concentration of the VS solution of 1 × 10–4 M. The neighboring adsorbate molecules can interact, forming siloxane dimers and trimers bound to the metal surface by either covalent or hydrogen bonds. Adsorption heats are calculated using different adsorption models. It is shown that VS is chemosorbed on the surface of zinc. An increase in the concentration of the VS solution up to 0.1 M results in formation of polycondensed siloxane oligomers on the surface with polycondensation degree n = 8–12. Oligomer surface fragments are connected with each other by hydrogen bonds and are connected with the surface by Zn–O–Si bridge bonds. The overall thickness of such a layer is 10–12 nm or ten molecular layers.

Magnetic Silica Bonding Perfluoroalkylsulfonylimide as Reusable Brønsted Acid Catalysts for Cellobiose Hydrolysis

New Bronsted solid acid, magnetic silica-supported perfluoroalkylsulfonylimide group was prepared. The as-synthesized functional siloxane oligomer was used to introduce perfluoroalkylsulfonylimide onto the magnetic core under the assist of TEOS, forming multi-layer core–shell structure, which was confirmed by TEM. The inner silica shell protected the acid-sensitive magnetic core from the corrosion of the strong acid; while the outer silica shell attached acid perfluoroalkylsulfonylimide groups. Good thermal stability (<229 °C) was expectable for the materials by TG analysis. The conclusive acid loadings of 0.61–0.69 mmol/g endowed the materials with efficient catalytic ability for the conversion of cellobiose to glucose (Glu), providing stable 85–91 % Glu yields throughout 3–4 cycles in water at 130 °C.

Inducing Elasticity through Oligo‐Siloxane Crosslinks for Intrinsically Stretchable Semiconducting Polymers

The promise of wearable and implantable devices has made stretchable organic semiconductors highly desirable. Though there are increasing attempts to design intrinsically stretchable conjugated polymers, their performance in terms of charge carrier mobility and maximum fracture strain is still lacking behind extrinsic approaches (i.e., buckling, Kirigami interconnects). Here, polymer crosslinking with flexible oligomers is applied as a strategy to reduce the tensile modulus and improve fracture strain, as well as fatigue resistance for a high mobility diketopyrrolopyrrole polymer. These polymers are crosslinked with siloxane oligomers to give stretchable films stable up to a strain ε = 150% and 500 strain‐and‐release cycles of 100% strain without the formation of nanocracks. Organic field‐effect transistors are prepared to assess the electrical properties of the crosslinked film under cyclic strain loading. An initial average mobility (μavg) of 0.66 cm2 V−1 s−1 is measured at 0% strain. A steady μavg above 0.40 cm2 V−1 s−1 is obtained in the direction perpendicular to the strain direction after 500 strain‐and‐release cycles of 20% strain. The μavg in the direction parallel to strain, however, is compromised due to the formation of wrinkles.

Simultaneous determination of five bioactive constituents in Rhizoma Chuanxiong by capillary electrophoresis with a carbon nanotube-polydimethylsiloxane composite electrode

A carbon nanotube (CNT)-polydimethylsiloxane (PDMS) composite electrode was developed for the capillary electrophoretic determination of the bioactive constituents in Rhizoma Chuanxiong, a traditional Chinese medicine. The novel composite electrode was fabricated on the basis of the in situ polyaddition of curing agent-containing dimethyl siloxane oligomer in the presence of CNTs in the inner bore of a piece of fused silica capillary under heat. It was coupled with capillary electrophoresis for the separation and detection of vanillin, ferulic acid, vanillic acid, caffeic acid, and protocatechuic acid in Rhizoma Chuanxiong to demonstrate its feasibility and performance. The five phenolic constituents were well separated within 13min in a 45cm long capillary at a separation voltage of 15kV using a 50mM borate buffer (pH 9.2). The CNT-based detector offered higher sensitivity, significantly lower operating potential, satisfactory reproducibility, and lower expense of operation, indicating great promise for a wide range of analytical applications.