Siloxane Compounds Research Articles

Siloxane Containing Polyether Groups-Synthesis and Use as an Anti-Biocorrosion Coating.

In the presented study, the effectiveness of a siloxane polyether (HOL7) coating on glass against microbiological colonization was assessed using microalgae as a key component of widespread aerial biofilms. The siloxane polyether was successfully synthesized by a hydrosilylation reaction in the presence of Karstedt's catalyst. The product structure was confirmed by NMR spectroscopy and GPC analysis. In addition, the thermal stability of HOL7 was studied by thermogravimetric measurement. Subsequently, the surfaces of glass plates were modified with the obtained organosilicon derivative. In the next step, a microalgal experiment was conducted. A mixture of four strains of algal taxa isolated from building materials was used for the experiment-Chlorodium saccharophilum PNK010, Klebsormidium flaccidum PNK013, Pseudostichococcus monallantoides PNK037, and Trebouxia aggregata PNK080. The choice of these algae followed from their wide occurrence in terrestrial environments. Application of an organofunctional siloxane compound on the glass reduced, more or less effectively, the photosynthetic activity of algal cells, depending on the concentration of the compound. Since the structure of the compound was not based on biocide-active agents, its effectiveness was associated with a reduction in water content in the cells.

In-situ two-dimensional temperature measurements using x-ray fluorescence spectroscopy in laminar flames with high silica particle concentrations

X-ray fluorescence spectroscopy (XRF) was used to measure temperatures and study mixing, for the first time in silica particle synthesis flames. Hexamethyldisiloxane (HMDSO) and trimethylsilanol (TMSO) were the particle precursors. A multi-element diffusion burner was used to produce a flat methane flame, and the precursors, dilute in inert gas, were injected via a central jet. Krypton was the fluorescent medium at 3.2 % concentration by volume. Scans with Kr in the central flow and not in the main flow were made to assess the mixing effects between the central and main gas flows. When HMDSO or TMSO were added, a secondary diffusion flame formed between the jet and the main methane flame. The results revealed a dramatic change in the centerline temperature profile of the jet gases when HMDSO or TMSO were added. The main methane flame stoichiometry also affected the temperature profiles. The results show HMDSO and TMSO reactions are initiated in a low-temperature and low-oxygen concentration region of the jet where thermal decomposition is not expected to be significant. Reaction of the particle precursors is therefore attributed to radical transport from the main methane flame. In the current work, particle number densities of up to 270 g/m3 locally are estimated. Thus, the study also demonstrates the capability of the XRF technique for high spatial fidelity measurements in flames with high concentrations of condensed-phase particles, leveraging the attribute that the XRF signal is generally not impacted by condensed-phase interferences. The observations and data obtained in this study inform likely reaction pathways for this important class of siloxane compounds.

Monitoring changes in hydric properties of treated stone material with conservation products by time-sequential IR thermography

A methodological approach for a semi-quantitative non-destructive testing (NDT) of the effects on hydric properties after the application of different conservation treatments (commercial ethylsilicate and siloxane compounds with consolidant, water repellent or consolidant + water repellent properties) is presented in this study. The NDT used for this purpose is a simplified method of time-sequential infrared thermography (IRT) on stone (granite and marble, treated and untreated) from the Roman theatre of Merida (Spain), which was listed by UNESCO as World Heritage Site in 1993.As water evaporation modifies temperature intensely, IRT enables monitoring the response of the stone samples during water absorption-evaporation processes. The comparative analysis between treated and non-treated specimens was performed by calculating the rate of surface apparent temperature change (ΔoC/h) value. The capillary rising test, monitored by IRT, clearly showed a different response of the samples treated with water-repellent treatments, proving their efficiency. Samples treated with organosilicic compounds showed a large and rapid drop in apparent surface temperature, indicating that water accesses rapidly.Results from the evaporation test also show this difference. The surface apparent temperature increased immediately in samples with water-repellent treatments, in which water does not enter inside stone, but remains on the surface. Samples with ethyl silicate, again, show a greater difference with respect to untreated samples, taking longer to recover surface apparent temperature, because the water is retained inside the stone for longer.This study proved simplified time-sequential IRT as a reliable technique for assessing the efficacy of conservation treatments applied to stone materials in laboratory.

Characterization and acid treatment of silica and organics in evaporator blowdown wastewater arising from SAGD operations

The evaporator blowdown (EBD) wastewater from high-pressure steam generation for the steam-assisted gravity drainage (SAGD) bitumen extraction process contains elevated concentrations of dissolved inorganic and organic compounds, of which silica and organics pose challenges in its treatment and disposal. This study investigated treatment options for EBD before its disposal. Following detailed physical and chemical characterization of the EBD, we examined its acid treatment with HCl and H2SO4 at pHs ranging from 12 to 2. The acid treatment performance was evaluated in terms of silica and organic removal efficiencies along with the filtration rate and filtrate recovery. Both acids gave similar silica and organic removal efficiencies; however, the filtration performance following the HCl-treatment was better than the H2SO4-treatment. In practice, the acids would likely perform comparably with regard to silica removal and the final process selection would more likely be influenced by other factors such as storage, material compatibility, cost, and downstream or subsurface compatibility. The HCl-treatment was investigated further with both the EBD and prepared silica solutions for the silica removal efficiency and filtration performance. The experiments conducted at ∼20 °C demonstrated higher silica removal efficiencies at pHs 10 and 8, whereas higher organic removal efficiencies were obtained at pHs 4 and 2. The experiments conducted at ∼80 °C showed enhanced silica removal at pH = 8 and higher organic removal at pH = 2. The precipitated solids were characterized using XRD and ATR-FTIR spectroscopy to identify the minerals and functional groups. The XRD patterns demonstrated that the solids generated were amorphous. The ATR-FTIR spectra revealed the predominance of siloxane, silanol, carboxylate and carbonyl compounds. These results confirmed a substantial removal of silica and organic constituents from the EBD through the acid treatment process.

Deposition of thin films on basalt fibers surface by atmospheric pressure plasma with different siloxane precursors

In this study, surface modification of basalt fibers (BFs) utilizing atmospheric pressure plasma deposition was carried out. Using this one-step deposition approach, three siloxane precursors with different structures including methyltrimethoxysilane (MTMS), hexamethyldisiloxane (HMDSO), and tetramethoxysilane (TMOS) were deposited on BFs surface, respectively. The physicochemical properties of the thin films from three different siloxane compounds are elucidated. In comparison with MTMS-coated sample, HMDSO-coated and TMOS-coated BFs surfaces feature an improved thermal insulation performance. The results demonstrate that atmospheric pressure plasma deposition is an efficient approach to modify flexible materials surface with improved thermal insulation. Moreover, it provides a reference to decide which precursor type is preferred for certain applications.

Cross-linking lignin and cellulose with polymers using siloxane compounds

Siloxanes are a group of substances characterized by Si-O-Si functional group. Siloxanes can react with alcohols to form Si-O-C bond. Siloxanes have been widely used as crossing linking agents and graft copolymers as well as additives for plastics. Lignin contains both phenolic and aliphatic hydroxy groups which have the potential to instigate bonding with siloxane compounds. However, there has not been any attempt to apply siloxanes as crosslinking agents for biobased composite formation. This manuscript presents the first study of applying siloxanes compounds to lignin and Cellulose nanofibers (CNF) with respective PLA, PETG, and HDPE to prepare biocomposites. Both Tetramethyl Tetraphenyl Trisiloxane (TTT) and Tetraethoxysilane (TEOS) were used as cross-linking agents. We have successfully incorporated 20 wt% lignin and 10 wt% CNF into the biocomposite filaments. The tensile properties of ensuing biocomposite were investigated. The objective of this work is to demonstrate the potential of lignin and CNF as a sustainable co-polymer to improve the properties of PLA/PETG/HDPE-based materials for 3D printing. This paper will also discuss the challenges and opportunities associated with the use of lignin in 3D printing, including the effect of lignin and CNF content on the mechanical and thermal properties, the compatibility of lignin and CNF with PLA/PETG/HDPE, and the potential for further optimization of the cross-linking chemistry using TTT and TEOS.

Hybrid Nanostructures Based of Ta2O5-PMMA for Electronic Applications

The scientific interest on hybrid materials is mainly related to understanding the types of interactions between inorganic and organic component and the effect of these interactions on the properties of the new material formed. Hybrid nanostructured materials and especially dielectrics are used for electronics (for gate layer) and especially those applicable in structure of different types of thin film transistors (TFTs).In this paper is presented the research on thin film hybrid materials based on tantalum oxide (Ta2O5) starting with inorganic precursor - tantalum ethoxide and polymethylmethacrylate (PMMA). The chemical method sol -gel involves the precursor-tantalum ethoxide which is hydrolysed and functionalized (with special siloxane compound), and the organic methyl methacrylate monomer. The chemical reactions take place at low temperature below 160 oC. The sol is deposited as thin films by spin-coating to analyse intensity-voltage (I-V) and capacitance-voltage curves (C-V) to determine the electric properties. Metal-Insulator-Metal (MIM) structures were made-up for electric characterisation. The value of leakage currents was between 10-10 - 10-7 A at ± 40 V. The hybrid films were analysed by scanning electron microscopy (SEM) for thickness and morphology and for thermal stability the sol was investigated by TG and DSC.The dielectric permittivity ranges between 3.5 and 4 at 1 MHz, depending on the tantalum alkoxide: MMA molar ratio, showing good behaviour for gate layer in future TFTs.

Dual-functional trisiloxane as binder additive for high volume expansion Li-ion battery electrodes

Silicon-based anodes for lithium-ion batteries have the inherent advantage of higher capacity. However, the inherent expansion of Si within the anodes during cycling, causing low battery life, has limited its application. Various approaches are being investigated to mitigate the adverse effects, ranging from the patterned deposition of Si, blending silicon materials with graphite active materials, and using modified polymeric binders. Inspired by the super spreading capabilities of siloxane compounds and with an aim to optimize the graphite-SiO composite electrode, this work focuses on tweaking the binder formulation with a trisiloxane-based additive which enables uniform dispersion of active material within the electrode and enhances the wetting of the electrolyte within the electrode. In this work, graphite with 15 wt% silicon monoxide was used as an electrode with trisiloxane-modified binder showing much improved electrochemical performance with better mechanical integrity compared to the benchmark electrode. The cell with modified binder exhibited remarkable cycling stability up to 400 cycles at 0.2 C-rate. A detailed study on the role of the trisiloxane additives on the physicochemical properties of electrode materials has also been elucidated. The prospects of employing these additives for similar high-volume expansion electrodes are also discussed.

Effects of solid-state fermentation of seaweed (Caulerpa racemosa) on antioxidant assay and flavour profile

The effects of solid-state fermentation (SSF) of Caulerpa racemosa on antioxidant properties (total phenolic content (TPC), 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, Ferric-reducing antioxidant power (FRAP)) and flavour profile were investigated. Additionally, sensory acceptability (9-Point Hedonic Test) and satiety analysis (10-Scale Intention) of oat drinks incorporated with SSF of C. racemosa were also studied. Results of SSF C. racemosa demonstrated that significantly (p<0.05) higher content in TPC, DPPH, IC50 and FRAP (312.30±5.76 mg GAE/100 g, 25.96±0.17 mg AA/100 g, 46.22±0.31 mg/mL, 1106.72±21.82 mg TE/100 g and 206.80±4.76 mg GAE/100 g, respectively). Flavour profile analysis indicated the presence of antimicrobial volatile siloxane compounds; hexamethylcyclotrisiloxane and octamethylcyclotetrasiloxane. These -siloxane group compounds are known to have antioxidant, defoaming, and release coating properties. In addition, results obtained from the sensory evaluation showed that the addition of a different amount of SSF C. racemosa did not significantly (p>0.05) affect the acceptability of instant oat drinks. However, oat drinks incorporated with SSF C. racemosa significantly (p<0.05) increased in fullness from the satiety study. Therefore, value-added SSF C. racemosa can be incorporated into food products to increase its nutritional properties and fullness without affecting the taste.

Green to Blue BODIPY Dyes for Fluorescent Applications in the Solution and the Solid State

The present study demonstrates the physical properties of BODIPY dye with efficient absorption and fluorescence phenomena in the green region of wavelength between (500-565) nm, the BODIPY dye adsorption over the solid state on polydimethyl siloxane PDMS, was studied. For this dye maximum absorption was at 500 nm and a BODIPY dye signal in the polydimethyl siloxane compound PDMS indicates the presence of adsorbed dye in the higher concentration of BODIPY dye. The fluorescence of this dye in chloroform was measured, this dye exhibited a maximum fluorescence at λem at 512 nm at different concentrations. The maximum absorption of BODIPY dye with green BODIPY dye, was located at 517 nm, while the maximum absorption of 5,5-difluoro-1,3,7,9-tertamethyl-10-(3,4,5-tris(dodecyloxy)phenyl)-5H-4λ4,5λ4-dipyrrolo[1,2-c:2’,1’-f][1,3,2]diazaborinine eh236f1 compound was located at 511 nm. On the other hand, the maximum absorption of BODIPY dye with blue BODIPY dye, was located at 517 nm.

Sterilization and reuse of masks for a standardized exhaled breath collection device by autoclaving

Exhaled breath research has been hindered by a lack of standardization in collection and analysis methodologies. Recently, the Respiration Collector for In Vitro Analysis (ReCIVA) sampling device has illustrated the potential to provide a consistent and convenient method for exhaled breath collection onto adsorbent media. However, the significant costs, compared to exhaled breath bags, associated with the standardized collector is believed to be the reason for limited widespread use by researchers in the exhaled breath field. For example, in addition to the sampling hardware, a single-use disposable silicon mask affixed with a filter is required for each exhaled breath collection. To reduce the financial burden, streamline device upkeep, reduce waste material, and ease the logistical burden associated with the single use masks, it is hypothesized that the consumable masks and filters could be sterilized by autoclaving for reuse. The masks were contaminated, autoclaved, and then tested for any surviving pathogens with spore strip standards and by measuring the optical density of cultures. The compound background collected when using the ReCIVA with new masks was compared to that collected with repeatedly autoclaved masks via thermal desorption gas chromatography mass spectrometry (TD-GC-MS). The capacity to block particulate matter of new filters was tested against that of autoclaved filters by introducing an aerosol and comparing pre-filter and post-filter particle counts. Finally, breath samplings were conducted with new masks and autoclaved masks to test for changes in measurements by TD-GC-MS of exogenous and endogenous compounds. The data illustrate the autoclave cycle sterilizes masks spiked with saliva to background levels (p = 0.2527). The results indicate that background levels of siloxane compounds are increased as masks are repetitively autoclaved. The data show that mask filters have significant breakthrough of 1 μm particles after five repetitive autoclaving cycles compared to new filters (p = 0.0219). Finally, exhaled breath results utilizing a peppermint ingestion protocol indicate two compounds associated with peppermint, menthone and 1-Methyl-4-(1-methylethyl)-cyclohexanol, and an endogenous exhaled breath compound, isoprene, show no significant difference if sampled with a new mask or a mask autoclaved five times (p > 0.1063). Collectively, the data indicate that ReCIVA masks and filters can be sterilized via autoclave and reused. The results suggest ReCIVA mask and filter reuse should be limited to three times to limit potentially problematic background contaminants and filter dysfunction.

Thiol-ene photopolymerization meets azide-alkyne click reactions: P/N/Si-containing, dual curable eugenol-based hybrid coatings

The use of bio-based building blocks for the synthesis of polymers is increasing day by day. Among the bio-based building blocks, eugenol is a highly promising monomer for the preparation of thermoset materials. In this study, we combined thiol-ene photopolymerization (TEP) and thermal azide-alkyne cycloaddition click reactions to prepare eugenol-based thermally stable, P-, N-, and Si-containing networks. To this end, we synthesized a P-containing, eugenol-based monomer bearing azide group and a siloxane compound containing an alkyne group. By mixing these monomers with multifunctional thiols and by utilizing a dual-curing strategy, we managed to obtain optically transparent and thermally stable coatings with excellent adhesion to glass substrates. Thermal stability, optical transmittance, pendulum hardness, solvent resistance, and the adhesion performance of the coatings were evaluated. The gel contents of the thermoset materials were found to be over 95%. At 600 °C, the char yields of the dual-cured coatings were found to be over 30%. Coatings were also found to be resistant to acidic and basic conditions as well as solvents.

Analysis of Organic Components in Various Butyl Rubber Closures and their Compatibility Study with Cefamandole Nafate by HPLC/GC-MS

Background: To control the quality of various butyl rubber closures and assess their applicability to cefamandole nafate, HPLC/ GC-MS methods were developed to qualitatively and quantitatively analyze the organic components in various types of butyl rubber closures and drug powder of cefamandole nafate for injection, and migration of these components from rubber closures to drug also were studied. Materials and Methods: The chemical components in the rubber closures and corresponding drug were identified by GC-MS in full scan mode and NIST mass library. A GC-MS method in SIM mode was established to quantitatively analyze siloxane compounds, aromatic hydrocarbons and saturated chain-hydrocarbons in rubber closures and drugs. An HPLC method was established to quantitatively analyze antioxidants and sulfides from rubber closures and drugs. The turbidity values of powder for injection were measured by a turbidimeter. Further, the correlation between the content of organic components in the drug and the clarity of the solution was analyzed. Results: It was found that the chemical components were released from butyl rubber closures and migrated to the drug, which influenced solution clarity of cefamandole nafate for injection and was the main factor to cause solution turbidity of powder for injection. The gradual migration of components occurred over time with the use of common butyl rubber closures, but the coated butyl rubber closures (rubber plated with membrane) were coated with a polytetrafluoroethylene film to block the contact between rubber closures and the drug, and could effectively prevent the migration of the components from rubber closures to drugs. The organic components in the butyl rubber closures were mainly identified as siloxanes, saturated chain-hydrocarbons, and antioxidants. An unknown ingredient was identified as 1-piperidinecarboxaldehyde, and trace amounts of toxic toluene were also detected within limits. Conclusion: It is suggested that rubber plated with membrane or rubber closures of high quality were applicable to cefamandole nafate for injection and should be used in its production. HPLC/ GC-MS methods can be used as an effective method for quality control of butyl rubber closures and compatibility research with drugs to ensure drug safety for the public.

COSMO prediction of siloxane compounds absorption on type 3 and type 5 deep eutectic solvents

This study reports a Conductor-like Screening MOdel for Real Solvents (COSMO-RS) prediction for 151 type 3 (polar) and type 5 Deep Eutectic Solvents (DES, non-polar) for absorption of hexamethyldisiloxane, octamethyltrisiloxane, hexamethylcyclotrisiloxane, and octamethylcyclotetrasiloxane. Through the examination of generated sigma surfaces, sigma profiles, and sigma potentials, it was found that while the siloxane chains offer sufficiently strong hydrogen bond accepting sites, the steric hindrance of the methyl groups cause less polar solvents (type 5) to outperform the more polar ones (type 3). The thermodynamic study predicts thymol-based type 5 DES as significantly more affinitive for siloxane compounds than common conventional solvents (DEA, MEA, MDEA, menthol, and DPEG Blend) with lnγ activity coefficients reaching low as −0.64. Enthalpy of mixing study shows Vander Waals interactions dominate DES-siloxane compound interactions over hydrogen bonding by over 10x enthalpic release, clarifying discrepancy in literature on how siloxanes are solvated by DES. Thymol: Stearic acid (4:1) showed the lowest excess enthalpy of mixing at −10.4 kcal/mol. An environmental health and safety (EHS) study show the best performing DES components (camphor, capric acid, lauric acid, myristic acid, stearic acid, undecenoic acid, borneol, betaine, hexadecanoic acid, and thymol) are potentially environmentally benign and safe for operation procedures.

The Macroalgal Biostimulant Improves the Functional Quality of Tomato Fruits Produced from Plants Grown under Salt Stress

Among the most perilous factors affecting tomato plant functioning and yield is salinity. The efficacy of halotolerant marine macroalgal extract of Chaetomorpha antennina (Seaweed Extract—SWE) in mitigating the toxic effects of salt stress (150 mM) in tomato plants to promote and enhance both plant functionality and yield was tested. It was evident that salt stress undesirably affected germination and plant growth in terms of quality and quantity. Treatment with SWE improved the functionality of salt-strained tomato plants by enhancing their germination indexes, growth and morphological traits, and photosynthetic pigments, as well as protein and phenol concentrations. SWE also exerted a positive influence on protecting the plant against salt stress by increasing the synthesis and accumulation of antioxidant enzymes, superoxide dismutase and lipoxygenase enzymes, along with the contents of lycopene and vitamin C. SWE also increased the nutraceutical quality, flavour and organolepty of emerged tomato fruits. GCMS analysis of fruit pericarp showed increased siloxane, phenol, antioxidant and indole acetic acid compounds, along with aromatic benzene compounds. These results indicate the potentiality of SWE in protecting plants against salt stress induced toxicities by prompting the synthesis of protective compounds such as siloxane and antioxidant enzymes. It was also noted that SWE plays a crucial role in promoting plant growth and survivability by improving plant functionality, yield and nutrition, by promoting cultivation in saline soils in an eco-friendly and sustainable manner.

Design and Performance of an Adsorption Bed with Activated Carbons for Biogas Purification.

Organic waste can be efficiently converted into energy using highly efficient energy systems, such as SOFCs coupled to the anaerobic digestion process. SOFC systems fed by biogenous fuels, such as biogas or syngas, suffer long-term stability due to trace compound impacts. It follows that, a mandatory gas cleaning section is needed to remove these pollutants at lower concentrations. This work investigates the adsorption mechanism for micro-contaminant removal through experimental results achieved using solid sorbents. Samples of different sorbent materials were analyzed in the laboratory to determine their performances in terms of sulfur (mainly hydrogen sulfide) and siloxanes (mainly D4-Octamethylcyclotetrasiloxane) adsorption capacities. The analysis shows that the chemical composition of the samples influences the adsorption of H2S (i.e., presence of calcium, iron, copper), while the effect of their textural properties mainly influences the adsorption of siloxane compounds, such as D4. A quantitative analysis was performed considering the influence of gas velocity on adsorption capacity. By increasing the biogas velocity (+45% and +89%), there was an indirect correlation with the H2S adsorption capacity (-27% and -44%). This identified an aspect related to the residence time required to be able to remove and retain the trace compound. The results obtained and summarized were used to develop a strategy for the removal of trace compounds in large-scale plants, e.g., for water purification.

A Silicon-Stereogenic Silanol - 18 O-Isotope Labeling and Stereogenic Probe Reveals Hidden Stereospecific Water Exchange Reaction.

A silicon-stereogenic aminosilanol was isolated in excellent diastereomeric ratio and the absolute configuration was determined. The silanol is configurative and condensation stable in solution and shows stereoselective transformations with a clean stereospecific pathway in follow-up reactions, which leads to the isolation of a silicon-stereogenic zinc complex and siloxane compounds. Investigations with 18 O-labelled water and mass spectrometry analysis revealed an otherwise hidden exchange of oxygen atoms of silanol and water in solution that proceeds with retention of the configuration at the silicon center. This novel combination of a stereochemical probe and isotopic labeling in a silicon-stereogenic compound opens new analytic possibilities to study stereochemical courses of reactions with the aid of chiral silanols mechanistically.

LP-08 Permitted Daily Exposure (PDE) assessment of data-poor pharmaceutical impurities using read-across (RA) approach: A case study with selected siloxane compounds

LP-08 Permitted Daily Exposure (PDE) assessment of data-poor pharmaceutical impurities using read-across (RA) approach: A case study with selected siloxane compounds

Evaluation of Physically and/or Chemically Modified Chitosan Hydrogels for Proficient Release of Insoluble Nystatin in Simulated Fluids.

To avoid fungal spreading in the bloodstream and internal organs, many research efforts concentrate on finding appropriate candidiasis treatment from the initial stage. This paper proposes chitosan-based physically or chemically cross-linked hydrogels aimed to provide sustained release of micronized nystatin (NYSm) antifungal drug, known for its large activity spectrum. Nystatin was demonstrated itself to provide hydrodynamic/mechanic stability to the chitosan hydrogel through hydrophobic interactions and H-bonds. For chemical cross-linking of the succinylated chitosan, a non-toxic diepoxy-functionalized siloxane compound was used. The chemical structure and composition of the hydrogels, also their morphology, were evidenced by infrared spectroscopy (FTIR), by energy dispersive X-ray (EDX) analysis and by scanning electron microscopy (SEM), respectively. The hydrogels presented mechanical properties which mimic those of the soft tissues (elastic moduli < 1 MPa), necessary to ensure matrix accommodation and bioadhesion. Maximum swelling capacities were reached by the hydrogels with higher succinic anhydride content at both pH 7.4 (429%) and pH 4.2 (471%), while higher amounts of nystatin released in the simulative immersion media (57% in acidic pH and 51% in pH 7.4) occurred from the physical cross-linked hydrogel. The release mechanism by non-swellable matrix diffusion and the susceptibility of three Candida strains make all the hydrogel formulations effective for NYSm local delivery and for combating fungal infections.

Preparation and properties of silicon-containing benzoxazine with high thermal stability

A silicon-containing benzoxazine (PDpsp-a) was synthesized from bis( p-hydroxyphenyl)diphenylsilane, aniline, and paraformaldehyde. The structure of the monomer was supported by 1H-NMR and FTIR spectra. The curing behavior of benzoxazine was evaluated by differential scanning calorimetry and in-situ FTIR spectra. The thermal properties were studied by MDSC, TGA, and Py-GC/MS. The results indicated that the characteristic peak of oxazine ring began to disappear when the temperature was heated to 180°C and completely disappeared at 260°C. The polybenzoxazine (PDpsp-a) possessed a high glass transition temperatures (174°C) and had good thermal stability (T10 = 420°C). In the pyrolysates of polybenzoxazine (PDpsp-a), no silicon-containing compounds, no phenol species, and more benzene were detected, we speculated that the Ar-Si bond would fracture with the increase of temperature. The benzene was volatilized from the system as a pyrolysis product and the silicon could react with oxygen to form siloxanes remained in the carbon residue in the form of siloxane compounds. The formed silica layer could endow the silicon-containing polybenzoxazine high thermal degradation stability and high char yield.