Search

The biomedical applications of silicones are countless due to their outstanding properties. In dentistry, silicone for maxillofacial and plastic surgery has become indispensable, from both physiological and aesthetic points of view. In this mini-review, silicone materials for dentistry and facial prostheses are discussed, focusing on their properties and alterations when exposed for long periods to different environments. A significant number of studies reported in the literature have been conducted in vitro, mimicking some of the main degradative factors which have been identified as triggers for discoloration and deterioration of the mechanical properties. Among these, in artificial aging and accelerated natural aging studies, UV radiation is considered the most important. Other weathering factors, biological contamination, and disinfection agents may have dramatic effects as well. Several general properties of silicones are described at the beginning, with a focus on biocompatibility, cross-linking mechanisms, and applications in dentistry and maxillofacial prosthetics. We discuss the ongoing cross-linking and/or possible exudation after manufacturing, which also affects the stability of the prosthesis over time, and possibly the patient. Next, the main environmental factors that affect the prostheses in service are presented, including the role of cigarettes smoke, which has been discussed very little so far. A few aspects, such as biofilm formation, its negative effects, and proposed solutions to overcome this phenomenon regarding silicones, are also described. We conclude by proposing a set of topics for future research and development based on the gaps that have been identified in the literature. Although silicones are probably irreplaceable in maxillofacial prosthetics, improvements in terms of base materials, additives, surface treatments, and maintenance are possible and necessary for long-lasting and safer prostheses. [ABSTRACT FROM AUTHOR]

Mesoporous silica nanoparticles (MSNs) bearing methyl, thiol or glucose groups were synthesized, and their encapsulation and release behaviors for the anticancer drug Doxorubicin (Dox) were investigated in comparison with nonporous homologous materials. The chemical modification of thiol-functional silica with a double bond glucoside was completed for the first time, by green thiol-ene photoaddition. The MSNs were characterized in terms of structure (FT-IR, Raman), morphology (TEM), porosity (nitrogen sorption–desorption) and Zeta potential measurements. The physical interactions responsible for the Dox encapsulation were investigated by analytic methods and MD simulations, and were correlated with the high loading efficiency of MSNs with thiol and glucose groups. High release at pH 5 was observed in most cases, with thiol-MSN exhibiting 98.25% cumulative release in sustained profile. At pH 7.4, the glucose-MSN showed 75.4% cumulative release, while the methyl-MSN exhibited a sustained release trend. The in vitro cytotoxicity was evaluated on NDHF, MeWo and HeLa cell lines by CellTiter-Glo assay, revealing strong cytotoxic effects in all of the loaded silica at low equivalent Dox concentration and selectivity for cancer cells. Atypical applications of each MSN as intravaginal, topical or oral Dox administration route could be proposed. [ABSTRACT FROM AUTHOR]

Isocyanides (isonitriles) are unique organic compounds that contain a formally divalent carbon. Herein, the synthesis of 1,3‐bis(isocyanopropyl)tetramethyldisiloxane was performed by a modified carbylamine method, using a phase transfer agent. Spectral methods (nuclear magnetic resonance [NMR], Fourier transform infrared spectroscopy [FT‐IR], and electrospray ionization mass spectrometry [ESI‐MS]) were used to confirm the structure. Energy gap of 1.86 eV (measured by diffuse reflectance spectroscopy [DRS]), high dielectric permittivity (15 at 10 kHz), and conductivity value in the order of 10−7 S·cm−1 place this compound in the range of wide‐bandgap semiconductors. The synthesis of Pt, Ag, and Fe metal complexes without organic co‐ligands and their catalytic activity were also investigated. The Pt complex was active in hydrosilylation reaction and in reduction of p‐nitrophenol, whereas the Ag complex was found effective in alkaline decomposition of hydrogen peroxide. The Fe complex is a new and cheap heterogeneous hydrosilylation catalyst and also showed very good catalytic behavior in heterogeneous Fenton‐like photodecomposition of Congo Red in various photo‐irradiation conditions, with 100% color removal efficiency after 60 min under sunlight. Thus, a simple path for siloxane‐containing materials with promising applications is open. [ABSTRACT FROM AUTHOR]

A spent catalytic converter was treated with concentrated HCl and hydrogen peroxide in very mild conditions to extract approximately half of its platinum group metals (PGMs) content, mainly as chlorides. The noble metals were subsequently charged into functionalized mesoporous silica by complexation with mercapto groups. A combination of methods was employed to prove the transfer of PGMs and to characterize the materials (inductively coupled plasma optical emission spectrometry [ICP‐OES], Fourier transform‐infrared [FT‐IR] spectroscopy, electrospray ionization mass spectrometry [ESI‐MS], thermogravimetric analysis [TGA], X‐ray photoelectron spectroscopy [XPS], X‐ray diffraction, and UV–Vis spectrophotometry). The resulted PGM‐loaded silica was successfully tested as a new heterogeneous catalyst for hydrosilylation and oxidation reactions. Information about the nature of the PGMs species extracted and loaded completes the existing literature data. The scrap cordierite may be valorized for retention of pollutants from water and also catalyzes the hydrosilylation reaction based on the remaining PGMs. Flexible composite materials can be obtained by incorporating scrap cordierite as filler and crosslinking catalyst into a silicone matrix, significantly enhancing the dielectric permittivity. Thus, complete re‐valorization of the main components of the catalytic converter as high‐added‐value materials was achieved at laboratory level, with very low energy demanding procedures. [ABSTRACT FROM AUTHOR]

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. [Display omitted] • Emulsion stabilized with a siloxane surfactant used as template at room temperature. • Porous silicones prepared by thiol-ene photoaddition or condensation cross-linking. • Mechanical properties and sensitivity tuned by composition and reaction type. • Piezocapacitive response with linearity on wide pressure domains. • Porous silicone-MWCNT composite with high sensitivity and gauge factor. [ABSTRACT FROM AUTHOR]

Functional siloxane dimmers and polymers carrying two types of hydrophilic groups (tris-(hydroxymethyl)aminomethane and 4-aminopyridyne) were previously prepared and characterized. Their surface properties were investigated by tensiometry, DLS and TEM in water or organic media. The un-modified methylsiloxane units induce hydrophobic character while the balance between the two moieties with antagonist behavior is responsible for self-assembling and surface activity, which can be tuned by adjusting the proportion of hydrophilic groups and the molecular architecture. Water soluble self-assembling functionalized siloxanes have been tested for biocompatibility by MTT method. They are efficient for stabilization of polymer nanoparticles of interest for drug delivery systems, encapsulation of hydrophobic drugs by micellar solubilization, and water dispersion of magnetic nanoparticles of interest for biomedical applications. The same compounds exhibit the ability to act as ligands for complexation of 3d and 4f –block metals, with implications in environment remediation and preparation of metallosurfactants or catalysts. In addition, pyridyl-modified siloxanes act as phase transfer agents for water soluble organic molecules. The previously reported properties and applications are summarized, compared and completed with new experiments, in order to show a broad picture of the applicative potential of these amphiphilic compounds. [ABSTRACT FROM AUTHOR]

Pyridyl functionalized siloxanes with various architectures were synthesized by addition of 4-amino-pyridine to epoxy-siloxanes. The polysiloxane precursors were prepared in house by combining ROP with hydrosilylation. Depending on the ratio between siloxane and polar functional groups, the pyridyl-modified compounds may be soluble in water, in organic solvents or both, exhibiting self assembling ability and particle stabilizing effect. Due to pyridyl groups, they act as ligands for 3d and 4f block metals. A particularly interesting application is concerned to their ability to transfer organic and inorganic molecules from water to the organic phase. This behavior was tested for silver clusters and for water soluble dyes and pH indicators. A possible end-use is foreseen for transparent colored polymers or removable/reusable pH indicators. The properties of the pyridyl-siloxanes can be tuned by synthesis. Thus, a lower content in siloxane groups leads to surface activity in water, while a higher amount of siloxane gives better phase transfer ability. [ABSTRACT FROM AUTHOR]

Three new metal–organic frameworks (MOFs) were obtained from a siloxane dicarboxylic acid (CX), 4,4′-bipyridyne (BPy) or 1,2-bis(4-pyridyl)ethylene (EBPy) and copper or cobalt acetates. The compounds were characterized by IR spectroscopy, powder X-ray diffraction, energy-dispersive X-ray fluorescence (XRF), thermogravimetric analysis (TGA), dynamic water vapor sorption (DVS), electron microscopy (TEM, SEM), UV–vis diffuse reflectance and fluorescence measurements. These hydrophobic MOFs acted as efficient catalysts in two processes occurring in aqueous media. The best result in alkaline decomposition of hydrogen peroxide was 90% conversion after 30 min. The catalytic activity in photodecomposition of Congo Red (CR) was followed in mild environmental conditions, i.e. under natural sunlight, without additional oxidation agents or pH adjustments. Unprecedented catalytic activity was found, especially for the Co complex with CX and EBPy, with discoloration efficiency of ca. 82% after 80 min of exposure to sunlight. The obtained results, in terms of rate constants and efficiency are comparable with those reported for other catalytic systems in photoreactors or in the presence of H 2 O 2 . The best catalyst was also tested in a Fenton-like process and it was found that the addition of H 2 O 2 doubles the rate constant and increases the efficiency to 97%. On the other hand, the remaining waters after CR photodecomposition were analyzed by mass spectrometry (ESI–MS) and it was concluded that “cleaner” water is obtained when the MOFs are used without addition of H 2 O 2 . [ABSTRACT FROM AUTHOR]

A series of polar silicones was synthesized in order to compare their dielectric properties. Different substituents with high dipole moment (epoxy, pyridyl, aldehyde, cyano-, nitroazobenzene) were attached by hydrosilylation to a poly(dimethyl-methylhydro)siloxane. Thiol-ene addition on a dimethyl-methylvinyl siloxane copolymer with similar composition was also used for chemical modifications with chloro- or carboxy- derivatives. This approach allowed comparison of properties with emphasis on dielectric behavior measured in liquid state, as a preliminary step in design and preparation of materials suitable for dielectric elastomers. Although a relatively low content of polar groups was used (8%), permittivity values of 5.4 and even 7.4 were achieved (at 10 kHz), either due to the large dipole moment or to the presence of important amounts of moisture. The water sorption capacity of the polar silicones was investigated by dynamic vapor sorption, while structural parameters of model molecules were calculated, in order to correlate the dielectric properties with the polarity/hydrophilicity of the substituents to the silicone chain. A combined effect of the calculated dipole moment, molar polarizability, molar volume, and the measured water sorption capacity on dielectric permittivity was observed. [ABSTRACT FROM PUBLISHER]

A tris(hydroxymethyl)aminomethane-modified polysiloxane has previously been investigated for surface properties and valuable practical applications have been proposed, including nanoparticle stabilization, complexing of 3d metals, micellar solubilization of drugs and water dispersion of metal oxide nanoparticles. In this article we show the ability of this multifunctional polymer to bind 4f metals. A polymeric lanthanum complex was obtained and characterized. The most probable structure was assigned based on ESI-MS and FT-IR, using data obtained with a homologous disiloxane model compound. The polymeric lanthanum complex shows surface activity, with a CMC value of 150 mg/L. Self-assembling in water was also studied by DLS and TEM, which revealed formation of vesicles. The La complex was tested with very good results for polymer nanoparticle stabilization. Polycarolactone nanoparticles of ca. 150 nm with long-term stability (Zeta potential = 55 mV) were obtained. The aqueous dispersion of organic-coated metal oxide nanoparticles was also successful. [ABSTRACT FROM AUTHOR]

Highlights: [•] Siloxane surfactants were found biocompatible by MTT cytotoxicity tests. [•] Stable water dispersions of SPION were obtained with these surfactants. [•] Good cell viability was found for aqueous dispersion of metal oxide nanoparticles. [•] Particles of 20–200nm with different morphology were observed by TEM. [•] SPION and an un-soluble drug can be dispersed together in surfactant vesicles. [ABSTRACT FROM AUTHOR]

Highlights: [•] A tromethamol-modified polysiloxane surfactant is investigated. [•] A method to dissolve nystatin in water is proposed using this surfactant. [•] The drug is physically encapsulated within the surfactant aggregates. [•] The in vitro antifungal activity was seriously improved. [Copyright &y& Elsevier]

Abstract: Two H-bond polymers from carboxypropyl disubstituted disiloxane and bipyridyl compounds, as well as the starting components in different ratios were reacted with zinc acetate. Two new siloxane-containing coordination polymers were thus obtained and characterized. They exhibited highly ordered structures, which were investigated by single crystal XRD. One of the H-bond polymers, as well as a third coordination polymer, without the siloxane component (obtained as secondary product) were also structurally characterized. The siloxane coordination polymer obtained with 4,4′-bipyridyl has a 2D MOF structure. The homologous polymer derived from 1,2-(4-bipyridyl)ethylene forms undulated 2D-layers which are packed in the crystal leading to partial interpenetration with formation of two types of channels along crystallographic axis c. The new siloxane-containing coordination polymers were investigated by FT-IR, DSC–TG–TGA, DVS and static contact angle measurements. They are hydrophobic (by contact angle) and even superhydrophobic effect was observed on bulk powder for one of them. The solvent sorption capacity was measured by tensiometry. They were tested for catalytic activity in H2O2 decomposition and preliminary experiments for oxidation of glucose and viscose were done. [Copyright &y& Elsevier]

Siloxane-containing polyazomethines with linear (PAZ) and cross-linked (CPAZ) architectures and their iron complexes (FePAZ and CFePAZ) have been prepared. The structures of the resulted compounds were investigated by spectral methods (FT-IR,1H NMR, UV–vis) and electrospray ionization mass spectrometry (ESI-MS). X-ray fluorescence spectrometry was used to determine the Si/Fe ratio and for quantitative analysis of silicon. Paramagnetic susceptibility (χ) and magnetic moment (μeff) of the soluble iron complex were estimated based on1H NMR measurements. The iron spin state was determined by Mössbauer spectroscopy, while the electrochemical behavior was studied by cyclic voltammetry. The catalytic activity in hydrogen peroxide decomposition reaction, in alkaline solution was tested. The compound FePAZ proved to increase the dielectric constant of a silicone matrix in which it was incorporated even in very low percent, acting also as an effective plasticizer. [ABSTRACT FROM PUBLISHER]

All-polymer composites were prepared in a simple manner from a pair of incompatible polymers: polysulfone (PSF) as the matrix polymer and cross-linked polydimethylsiloxane (PDMS) submicron particles as the disperse phase. The obtained composites, containing approximately 50 wt.% of PDMS particles, were compared with neat PSF and with blends of the two components. Scanning electron microscopy coupled with Energy Dispersive X-Ray analysis (SEM-EDX), dynamo-mechanical analysis (DMA), dynamic contact angle measurements, and thermogravimetric analysis (TGA) showed unitary materials, with particles well dispersed across the section and having dynamo-mechanical and surface properties comparable with the neat PSF or even improved. [ABSTRACT FROM AUTHOR]

A simplified alternative for the synthesis of carbohydrate-modified siloxanes is described. The starting siloxane precursors contain glycidyl functional groups, which react with glucose in dimethylformamide (DMF), in the presence of a gel type cation exchanger. The method eliminates protection-deprotection reactions, as well as moisture-sensitive or multiple reaction steps. Glycidyl-functionalized siloxane compounds are commercially available, but can be easily obtained in the desired architecture or chain length by hydrosilylation. Two examples are presented, describing the synthesis of a glucose-modified disiloxane and a siloxane copolymer bearing pendant glucose units. 1H and 13C nuclear magnetic resonance (NMR), and infrared spectroscopy (FT-IR) were used to confirm their structure. Evidence for the preservation of the polysiloxane chain after the reaction was obtained by 1H-NMR, thus confirming the non-invasive role of wet gel-type cation exchanger in chemical modifications of siloxane copolymers. The water-soluble disiloxane compound exhibited typical surfactant behavior, with a critical micelle concentration (CMC) value of 6.3 × 10−4 mol/L (determined by tensiometry) and an equilibrium surface tension of 32.8 mN/m. The obtained copolymer, incompletely modified with glucose, exhibited two glass transition temperatures by Differential Scanning Calorimetry (DSC). [ABSTRACT FROM AUTHOR]

Three poly(arylene ether sulfone)s (two polymers and one copolymer) containing diphenylfluorene, phenolphthalein and 2,4-bis[(4-chlorophenyl)sulfonyl]-1-(phenyltio) benzene)] units were synthesized by the classical Williamson polyetherification reaction. The association phenomenon in N,N-dimethylformamide (DMF) was investigated by different methods: gel permeation chromatography (GPC), viscosity, atomic force microscopy (AFM), fluorescence spectroscopy and dynamic light scattering (DLS). Both AFM and DLS measurements evidenced the formation of aggregates with spherical or ellipsoidal shape at a concentration around 0.05 wt.%. This behavior could be explained by dipole-dipole interactions between macromolecular chains, probably with the participation of solvent molecules, and by H-bonds involving hydroxyl end groups. [ABSTRACT FROM AUTHOR]

Abstract: New complexes of the composition: {Fe3O(OOCR1COO)3}+ and {Fe3O(R2COO)6}+, where R1 = –(CH2)3–Si(CH3)2–O–Si(CH3)2–(CH2)3– or –(CH2)8–COO–CH2–Si(CH3)2–O–Si(CH3)2–CH2–COO–(CH2)8–; R 2 = Si(CH3)3–O–Si(CH3)2–CH2–COO–(CH2)8–, were synthesized by direct synthesis using siloxane carboxylic salts and iron nitrate or by ligand exchange in μ3-oxo trinuclear iron(III) acetoxy-cluster with siloxane carboxylic acids. The obtained compounds have been characterized by elemental analysis, FT–IR and UV–Vis spectroscopy, mass spectrometry (ESI–MS), thermal analysis, Mössbauer spectroscopy, and magnetic measurements. By ESI–MS, in the starting iron acetate dodecanuclear cluster was detected besides the trinuclear compound. The new siloxane-containing iron(III) clusters showed a bathochromic shift in UV–Vis spectra compared to the acetate. The thermal decomposition starts above 200 °C and higher thermal stability was observed for the clusters with sebaco-siloxane diacid. The Mössbauer spectroscopy data indicate the presence of iron(III) in a high spin state. By using a potassium salt of sebacomethylpentamethyldisiloxane as a reactant and stabilizer, iron cluster nanoparticles were obtained, both by direct synthesis and ligand exchange. According to all our data, the direct synthesis is a more convenient reaction path, in terms of reaction conditions and purity of the final products. [Copyright &y& Elsevier]

Polysulfone−silver composite nanoparticles have been prepared by combining polymer nanoprecipitation and redox synthesis of silver, in the presence of a glucose-modified cyclosiloxane as stabilizing agent. Based on previous kinetic investigations and on model reactions, we concluded that the reducing agent in this case is the tetrahydrofuran (THF) used as solvent for polysulfone. Dynamic light scattering measurements on the obtained polymer-silver composite particles indicated particle average diameter of 176 nm with a polydispersity index of 0.25. The UV-vis spectrum exhibited the silver plasmon resonance. By different microscopic methods (atomic force microscopy-AFM, high resolution transmission electron microscopy-HRTEM, and scanning electron microscopy-SEM), larger polymer particles coated with silver nanoprticles were observed. The Energy Dispersive X-Ray analysis-EDX; confirmed the presence of Ag on the surface of the particles, while the selected area electron diffraction showed single crystalline silver nanospheres with face-centered cubic structure. [ABSTRACT FROM AUTHOR]

Polydimethylsiloxane-α,ω-diols with different contents of pendant chloromethyl groups were reacted with an aromatic diamine (3,3′-dimethoxybenzidine) when cross-linking occurred. The reactions were performed in silica — generating sol— gel system; so two interconnected networks (silica and cross-linked polydimethylsiloxane) were formed. The resulting structures were investigated by FT-IR and 1H-NMR spectroscopies. Differential scanning calorimetry was used to emphasize the thermal transitions of the resulted materials and the water sorption capacity was investigated by dynamic vapor sorption, the obtained values being influenced by the amount of polar groups. Atomic force microscopy was used to evaluate the morphology and surface topography in dry as well as in swollen state in water and heptane. [ABSTRACT FROM AUTHOR]

Silver nanoparticles were obtained in aqueous medium, at room temperature, by redox reactions, with or without glucose, in the presence of a glucose-containing cyclosiloxane. The siloxane surfactant can act as stabilizer when glucose is present in the system, but also as reducing agent and stabilizer when no glucose is added. The kinetics was followed by absorption UV–Vis spectroscopy, and different behaviors were found for the two versions of the redox process: first-order kinetics for the reaction with glucose and a much slower complex reaction with three zero-order steps when no glucose was added. The reactions were also investigated with IR absorption spectroscopy. The resulting nanoparticles were analyzed by dynamic light scattering (DLS), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX) analysis, and transmision electron microscopy (TEM). All data showed evidence for the formation of silver spherical nanoparticles, with an average diameter of 14 nm (reaction with glucose) and 6.5 nm (reaction without glucose), respectively. [ABSTRACT FROM AUTHOR]

Cellulose acetate was reacted in different ratios with poly[dimethyl(methyl-H)siloxane] containing 25 mol% Si–H side groups along the chain. A dehydrocoupling reaction between Si–H and C–OH groups occurred in presence of Karstedt’s catalyst, leading to the formation of Si–O–C bond, as proved by FTIR spectra, thus crosslinking the cellulose derivative. The networks were processed as films by casting before the end of the reaction and were investigated by different techniques to emphasize the morphology, thermal, dielectric and surface properties developed in correlation with the ratio between the two involved components (cellulose and siloxane derivatives). A decrease of the dielectric constant values of cellulose acetate was noticed throughout the studied frequency and temperature range as a result of crosslinking. [ABSTRACT FROM AUTHOR]

New siloxane-based amphiphilic compounds (a dimer and two copolymers with pendant functional groups) have been synthesized starting from tris(hydroxymethyl)aminomethane (tromethamol) and glycidyl-functionalized siloxane precursors. They have been characterized by spectroscopic methods (Fourier transform infrared (FTIR) spectroscopy and 1H-nuclear magnetic resonance (NMR)) and their surface properties have been investigated by tensiometry. Surfactant behavior in water (for the dimer and a copolymer with 1.5/1 dimethyl/hydrophilic group ratio) or dimethylformamide (DMF) (for a copolymer with lower hydrophilic content) was emphasized. Low critical micelle concentration (CMC) values and equilibrium surface tensions were detected. By dynamic contact angle measurements, very good wetting behavior towards glass was observed. [ABSTRACT FROM AUTHOR]

A high molecular weight dimethylmethylvinylsiloxane copolymer (Mv=450, 000) has been synthesized, analyzed, and used as matrix to prepare a composite by mixing with a proper amount of silica. A mixture of Fe2O3/TiO2 was added to obtain a color close to the natural. 2,4-Dichlorobenzoyl peroxide was also incorporated as a crosslinking catalyst. This heat curable silicone-based formulation was used for relining removable dental prosthesis. The optimum conditions to appliance and hardening of the silicone composite on the prosthesis were established. The main surface (morphology, water contact angle, and water vapor sorption capacity) and mechanical characteristics were evaluated for the crosslinked silicone processed as thick film. The prosthesis relined with silicone was tested on a machine simulating mandible biomechanics both from kinematics and dynamic points of view. The results revealed a good behavior of our composite that remained unmodified after 700,000 mastication cycles. [ABSTRACT FROM AUTHOR]

Polymer-dispersed liquid crystals (PDLCs) composed of poly(dimethyl siloxane), cured poly(dimethyl siloxane) and polysulfone (as matrices), and an azomethine compound (as an embedded mesogen varying in weight from 5 to 80%) were prepared via solvent-induced phase separation. After preparation, they were heated to the melt and then cooled; phase transitions upon both heating and cooling were detected with a differential scanning calorimeter and a polarising optical microscope (POM). The nematic droplets appearing in the POM images across the isotropic-nematic phase transition were treated statistically and described with principles of irreversible thermodynamics. Furthermore, kinetics of the nematic phase growth across this phase transition was studied and described analytically with the universal law for cluster growth. Both flexibility of the polymer matrix and the mesogen content in PDLCs were shown to influence the processes studied. [ABSTRACT FROM AUTHOR]

Thermal and thermo-oxidative stability of some poly(siloxane-azomethine)s obtaining starting from bis(formyl- p-phenoxymethyl)tetramethyldisiloxane and different organic diamines have been investigated by TG+DTG+DSC simultaneous analyses performed in argon flow and air static atmosphere, respectively. TG, DTG and DSC curves of each polymer showed three or four successive degradation steps at different temperatures according to the composition of the sample and the gaseous atmosphere in which the thermal analysis was performed. For each process, the following parameters were evaluated: total mass loss, temperature corresponding to the maximum reaction rate, maximum reaction rate, temperature corresponding to certain mass loss. In order to determine the thermal and thermo-oxidative stabilities of investigated polymers, the following values were determined: T x% — temperature corresponding to x% mass loss, and %Δ m T — mass loss at a given temperature T. The obtained orders of stability were correlated with the structure of investigated polymers. [ABSTRACT FROM AUTHOR]

The aliphatic siloxane-arylidene sulfone-segmented copolymers were investigated using an optical microscope at temperatures above their glass transitions. In the images obtained for thin layers, segregated micro-domain structures were recognized and characterized statistically. Subsequently, the statistical size distribution of micro-domains was described using the model of reversible aggregation. The distribution parameters related to the mean size and dispersion were shown to change regularly with the chemical composition of the copolymers. For thicker layers of the copolymers, a tendency to coalesce was revealed. In this case, two hierarchically organized statistical ensembles of micro-domains were recognized. [ABSTRACT FROM AUTHOR]

Two series of modified polysulfones containing siloxane-aliphatic pendant moieties were analysed by optical microscopy, transmission electron microscopy, electron diffraction, contact angles measurements and X-ray photoelectron spectroscopy (XPS or ESCA), in order to establish the microstructure and surface properties. All samples exhibited biphasic bulk morphology due to a crystallization tendency induced by the pendant moiety, and silicon enriched surface irrespective of the substitution degree. The values of the surface tension calculated from contact angle measurements were in agreement with the hypothesis of surface enrichment. [Copyright &y& Elsevier]

Presents a study which described the synthesis and characterization of some poly-(siloxane-ester-maleimides) by solution polycondensation of different bis(dichloro-maleimides) with the sodium salt of bis(1,3-sebacomethyl)-1,1,3,3-tetramethyldisiloxane. Methodology; Results and discussion; Conclusions.

Polydimethylsiloxane (PDMS), in spite of its well-defined helical structure, is an amorphous fluid even at extremely high molecular weights. The cause of this behavior is the high flexibility of the siloxane backbone and the lack of intermolecular interactions attributed to the presence of methyl groups. These make PDMS incompatible with almost any organic or inorganic component leading to phase separation in siloxane-siloxane copolymers containing blocks with polar organic groups and in siloxane-organic copolymers, where dimethylsiloxane segments co-exist with organic ones. Self-assembly at the micro- or nanometric scale is common in certain mixed structures, including micelles, vesicles, et cetera, manifesting reversibly in response to an external stimulus. Polymers with a very high degree of ordering in the form of high-quality crystals were obtained when siloxane/silane segments co-exist with coordinated metal blocks in the polymer chain. While in the case of coordination of secondary building units (SBUs) with siloxane ligands 1D chains are formed; when coordination is achieved in the presence of a mixture of ligands, siloxane and organic, 2D structures are formed in most cases. The Romanian research group's results regarding these aspects are reviewed: from the synthesis of classic, amorphous silicone products, to their adaptation for use in emerging fields and to new self-assembled or highly ordered structures with properties that create perspectives for the use of silicones in hitherto unexpected areas. [ABSTRACT FROM AUTHOR]

Polysulfone-supported silver nanoparticles (Ag@PSF) were obtained by a combination of polymer nanoprecipitation and redox synthesis of silver, in the presence of two siloxane-based stabilizing agents, and were incorporated into a PDMS matrix. Soft elastic composites (PDMS-Ag@PSF) were obtained and were investigated by dielectric relaxation spectroscopy and tensile measurements, in comparison with similar materials containing either PSF particles or AgNPs. The mechanical properties of the composites are tunable by composition, depending quasi-linearly on the Ag content. A PDMS-Ag@PSF film with 0.8 wt% Ag, having Y = 0.12 MPa, maximum strain 550% and E BD = 36 V μm−1 exhibited electrical actuation of 8% lateral strain at 22 V μm−1. Apparent piezoelectric coefficient d 33 values of ~15 pm V−1 were measured by piezoresponse force microscopy for the composites with Ag@PSF, showing a synergistic effect of the fillers' components. In addition, the materials exhibited antibacterial and antifungal activity and low bioadhesion. Based on their properties, the highly stretchable composites can be regarded as candidates for applications like actuators, sensors or micro/nanogenerators in biomedical field. Image 1 • Polysulfone-supported silver nanoparticles stabilized with siloxane surfactants. • PDMS-Ag@PSF composites with tunable mechanical and dielectric properties. • Electric actuation response of 8% lateral strain at 22 V/μm. • Apparent piezoelectric coefficient d 33 of 15 pm V-1 measured by PFM. [ABSTRACT FROM AUTHOR]

• Multi-stimuli-responsive free-standing silicone films. • Polysiloxanes modified on chain with carboxyl and nitro-azobenzene groups. • High dielectric permittivity, breakdown strength and electrical actuation. • Piezoelectric response and polarizability at low temperature without poling. • Preferential photoactuation depending on optical and mechanical properties. Multi-functional materials were synthesized by on chain modification of dimethyl-methylvinylsiloxane copolymers with mercaptopropionic acid and Disperse Red 1 (DR1). After cross-linking, transparent free-standing films were obtained, showing at the same time light-responsive and electromechanical (electrical actuation and piezoelectric) properties. Different characterization tools, such as DSC, dielectric broadband spectroscopy, dynamic contact angle, and indentation, were applied to investigate the impact of polymer functionalities on the intrinsic material properties. The molecular grafting of DR1 enhanced the dielectric permittivity by 63% compared with the starting vinyl-silicones, while high breakdown strength of 84 V/μm was achieved. The films exhibited actuation on three different mechanisms: electrical, piezoelectric and photo-induced. Through the use of specific analyzing techniques (such as electric field actuation, piezoresponse force microscopy -PFM- and photoactuation) direct evidence of these features was brought in each case. The lateral actuation strain reached 8.7% at 40 V/μm, as a consequence of increased dielectric permittivity. The piezoelectric coefficient d 33 of about 10 pm/V was determined by PFM. The trans – cis photoisomerization of nitro-azobenzene which occurs during UV irradiation led to surface modifications and preferential actuation of the film (such as, length change or bending), depending on optical and mechanical properties of the materials. [ABSTRACT FROM AUTHOR]

Although platinum nanoparticles and complexes ‐especially of Pt(0) and Pt(II)‐ are well known catalysts, siloxane‐based platinum complexes are rarely reported. Herein, a Platinum(IV) complex of 4‐aminopyridinium‐modified disiloxane was prepared and characterized by medium and far infrared spectroscopy, NMR and EDX. The formation of the complex was monitored by UV–Vis spectroscopy, which showed the high affinity and selectivity of this ligand for Pt, with a stability constant of 7.53·103 M−1. The catalytic activity of the siloxane‐based complex was tested in three types of reactions: reduction of p‐nitrophenol, oxidation of glucose and starch, and hydrosilylation. The hydrophobic behavior of the permethylated disiloxane moiety ensures good hydrolytic stability, while the N‐donor ligand stabilizes the in‐situ formed Pt nanoparticles. The generation of Pt nanoparticles during p‐nitrophenol reduction was confirmed by TEM and SEM. Contrary to most reports, the aerobic oxidation of mono‐ and polysaccharides occurred without oxidation agents or mediators added, in mild conditions, at room temperature and pH ~9. The same metal complex was found active in hydrosilylation of vinyl‐siloxanes with temperature‐modulated rate, thus being useful in silicone cross‐linking systems without the need of inhibitors. The method was adapted to one‐pot synthesis of silica‐supported Pt(IV) complex, which acted as efficient and reusable heterogeneous hydrosilylation catalyst, limiting the contamination of the product with Pt. This approach is promising for superior valorization of scarcely available and expensive platinum metal. By the same method, multifunctional soluble complexes and mesoporous silica may be obtained, with tunable catalytic performance. [ABSTRACT FROM AUTHOR]

Although it is known (from the observations of medical professionals) that cigarette smoke negatively affects maxillofacial prostheses, especially through staining/discoloration, systematic research in this regard is limited. Herein, the color modifications of M511 maxillofacial silicone, unpigmented and pigmented with red or skin tone pigments, covered with mattifiers, or with makeup and mattifiers, and directly exposed to cigarette smoke, were investigated by spectrophotometric measurements in the CIELab and RGB color systems. The changes in color parameters are comparatively discussed, showing that the base silicone material without pigmentation and coating undergoes the most significant modifications. Visible and clinically unacceptable changes occurred after direct exposure to only 20 cigarettes. By coating and application of makeup, the material is more resistant to color changes, which suggests that surface treatments provide increased protection to adsorption of the smoke components. The dynamic water vapor sorption (DVS) measurements indicate a decrease of the sorption capacity in pigmented versus unpigmented elastomers, in line with the changes in color parameters. [ABSTRACT FROM AUTHOR]

Amassing remarkable properties, silicones are practically indispensable in our everyday life. In most classic applications, they play a passive role in that they cover, seal, insulate, lubricate, water-proof, weather-proof etc. However, silicone science and engineering are highly innovative, seeking to develop new compounds and materials that meet market demands. Thus, the unusual properties of silicones, coupled with chemical group functionalization, has allowed silicones to gradually evolve from passive materials to active ones, meeting the concept of "smart materials", which are able to respond to external stimuli. In such cases, the intrinsic properties of polysiloxanes are augmented by various chemical modifications aiming to attach reactive or functional groups, and/or by engineering through proper cross-linking pattern or loading with suitable fillers (ceramic, magnetic, highly dielectric or electrically conductive materials, biologically active, etc.), to add new capabilities and develop high value materials. The literature and own data reflecting the state-of-the art in the field of smart silicones, such as thermoplasticity, self-healing ability, surface activity, electromechanical activity and magnetostriction, thermo-, photo-, and piezoresponsivity are reviewed. [ABSTRACT FROM AUTHOR]

Three complexes of copper with organosiloxane ligands of bis-azomethine type derived from 1,3-bis(3-aminopropyl)tetramethyldisiloxane and 2-hydroxybenzaldehyde (1), 5-nitro-2-hydroxybenzaldehyde (2), and 3,5-di-tert-butyl-2-hydroxybenzaldehyde (3) having well-established structures were investigated for their ability to form aggregates in organic solvents, namely dimethylformamide. The thermal behavior in solid state was investigated by thermogravimetrical analysis (TGA) and differential scanning calorimetry (DSC), the results being correlated with the structure and intermolecular interactions highlighted by crystallographic analysis. The co-existence in these structures of nonpolar 1,3-bis(propyl)tetramethyldisiloxane moiety and a polar one, consisting in metal complexed through hydroxy-azomethine groups, makes them able to self-assemble both in solid state and in solution. The surface activity of the complexes was evaluated by surface tension measurements, whereas the formation of the aggregates in solution was emphasized by UV-Vis spectroscoppy, dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) analyses. The DSC curves recorded in solution revealed the presence of large endotherms in the range 30–100°C, which prove the presence of the aggregates. The preservation of these assemblies after solvent evaporation was studied by transmission electron microscopy (TEM) and atomic force microscopy (AFM). [ABSTRACT FROM PUBLISHER]

Two octakis(carboxyalkyl-thioalkyl)silsesquioxanes (COOH-PSx) were obtained by click photo-induced thiol-ene addition reactions between octavinyl-T8-silsesquioxane and thioalkylcarboxylic acids. Their structures were confirmed by elemental and spectral analyses and in one case by single-crystal X-ray diffraction. The natrium salts of COOH-PSx were used as very efficient ligands for Cu, Ni and Cd ions. The formation of transition metals complexes was confirmed by FT-IR spectroscopy, showing the coordination pattern, and by EDX semiquantitative elemental analysis. They were analyzed in terms of thermal stability, morphology and moisture sorption. The catalytic activity was tested in alkaline decomposition of hydrogen peroxide, the copper complexes showing the best activity, that is 40% conversion after ~ 40 min. A copper complex was also efficient as catalyst in photodecomposition of Congo Red under UV light, without additional oxidation agents or pH adjustments, showing discoloration efficiency of ca. 89% after 145 min and recycling ability. Thus, the results indicated the compounds reported here, obtained by simple and reproducible synthetic protocols, as efficient, stable and re-usable heterogeneous catalyst. The possibilities of structural diversification (by the nature of the functional groups and the metal ion) are wide and of the application potential. [ABSTRACT FROM AUTHOR]

Although silicones possess low dielectric constant, they are between the most used polymers in actuation due to their appropriate mechanical properties (low modulus and high elongation). These can be easily tuned by the preparation strategy: proper choice of the molecular mass and microstructure of the polymer matrix; adding or not of more or less active fillers; whether these are incorporated in the polymeric matrix (ex situ) or generated in situ; crosslinking mode (through the side or ending functional groups) or mechanism (condensation, radicalic or by hydrosilylation). A relatively low cost and easy scalable procedure was used in this article to prepare silicone composites based on high molecular weight polydiorganosiloxane copolymer and hydrophobized silica and titania nanoparticles. The matrix polymer was synthesized by bulk ring opening copolymerization of different substituted cyclosiloxanes and characterized by FTIR, 1H NMR and gel permeation chromatographic analysis. The composites prepared by the mechanical incorporation of the fillers were crosslinked by radicalic mechanism and investigated by dielectrical spectroscopy, mechanical tests, dynamo-mechanical analysis and dynamic vapor sorption. The actuation measurements revealed displacement values in the range 0.04–5.09 nm/V/mm, while energy harvesting measurements revealed impulse electrical voltage in the range 6–20 V for a dynamic force of 0.1–1 Kgf. The robustness of these composites supported by their thermal, mechanical and surface properties recommends them for use inclusively in harsh environmental conditions, when their behavior is not significantly affected. [ABSTRACT FROM PUBLISHER]

Abstract: Two new polymeric structures containing ferrocene units along the chains, namely poly(silyl ester)s, have been synthesized and characterized: a geminal poly(silyl ester) (g-PSE) and one having a disiloxane spacer between the silyl ester groups (s-PSE). The condensation polymerization of AA/BB monomer systems in solution was used in both cases as preparation method involving a silicon-containing diol, (diphenylsilane diol or 1,3-bis(hydroxy)-tetramethyldisiloxane), and 1,1′-di(chlorocarbonyl)ferrocene. The polymers were investigated by differential pulse voltammetry in order to evaluate the redox behavior. Due to the presence of the silyl ester groups in the chain, these polymers are hydrolytically degradable. [Copyright &y& Elsevier]

New poly(anhydride)s containing amino acids and siloxane segments have been synthesized. The synthetic method involves the polycondensation in solution of the organic diacids (N-trimellitylimidoglycine, 1a, N-trimellitylimido-γ-aminobutiric acid, 1b, and N-trimellitylimido-ϵ-aminocapronic acid, 1c) obtained from the proper amino acids with a siloxane diacid (1,3-bis(3-carboxypropyl)tetramethyldisiloxane, 2a, α,ω-bis(3-carboxypropyl)oligodimethylsiloxane, 2b, or 1,3-bis(sebacomethyl)tetramethyl-disiloxane, 2c). The acetylation method was used for the activation of the two types of diacids (organic and siloxanic). Optimization of synthesis parameters was made.The structures and morphology of partial and final products were determined by IR and 1H NMR spectroscopy and differential scanning calorimetry. Inherent viscosities were determined and some preliminary solubility and hydrolytic stability tests were also performed. [Copyright &y& Elsevier]

The present paper presents the preparation and characterization of Ni complex of a guanidine functionalized trisiloxane as a model compound for polysiloxanes supported metal complexes. The structures of the ligand and its Ni complex are elucidated by theoretical calculations using semi-empirical PM6 and DFT methods, and experimentally confirmed by IR, UV, NMR, SEM and EDX. Thus, a 1/1 ligand/Ni complex with a tetragonal structure was established. As proved by ATG and DSC analysis, the Ni complex is stable up to about 170 °C and is characterized by a Tg value of 25 °C in dry state. Dielectric measurements revealed a conductivity of 5.6 × 10−7 S cm−1 at 25 °C for the Ni complex, about ten times higher as compared to that of the ligand, due to the reduction of the conduction activation energy induced by the presence of the metal. [ABSTRACT FROM AUTHOR]

Abstract 1,3-divinyltetramethyldisiloxane (V2), 1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane (V3), and 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (V4) are used as hydrophobic substrates to attach carboxyl groups by thermal or photochemical activated thiol-ene addition of 3-mercaptopropionic acid (R1), thioglycolic acid (R2) and thioacetic acid (R3). The reactions occurrence is monitored by IR following the disappearance of specific absorption bands for -S-H and –CH=CH 2 bonds. At the end, the structure of the compounds and thioetherification degree of vinyl groups are determined by NMR. Co-existence in the structure of the highly hydrophobic methyl group and the carboxyl or carbonyl group gives the compounds formed an amphiphilic character, as indicated by the calculated hydrophilic-lipophilic balance, making them capable of self-assembling in solution, as the results of the dynamic light scattering (DLS) and nanoparticle tracking analysis (NTA) measurements also show. Under normal temperature conditions, these compounds are in the liquid state. The DSC measurements in the range (−150) – (+150) reveal only a glass transition in the negative field and no other thermal transitions or decomposition processes. This behavior could make these compounds containing polar groups useful as solvent-free liquid electrolytes. Dielectric spectra reveal an increase in both dielectric permittivity and conductivity of the thiol-ene addition products as compared with starting vinyl-siloxanes. The increase is even more significant after doping with lithium salt, reaching conductivity values of order 10−4 S/cm. Highlights • Methylvinylsiloxanes are functionalized with carboxyl groups by thiol-ene addition. • The compounds are in a liquid state in a wide temperature window. • Amphiphilic nature is proved by theoretical calculations and experimental measurements. • In solution, the compounds self-assemble to form aggregates proved by video images. • Compounds exhibit conductivities up to 10−4 S/cm when are in Li-doped form. [ABSTRACT FROM AUTHOR]

Octakis(2-carboxyethyl-thioethyl)silsesquioxane (T 8 -COOH), a structurally well-defined organo-functionalized nano-silica, was used as an addition in different percentages (up to 15 wt.%) to a high molecular mass PDMS, obtaining composites that were processed as films by solution casting and stabilized by condensation crosslinking. SEM images showed a common aggregation phenomenon within polymeric matrix at high filler concentration. The presence of T 8 -COOH pushed the main stage of thermal decomposition to higher temperatures, generally around 500 °C, as compared to 400 °C for pure PDMS. The mechanical strength of the obtained composites was also enhanced by increased addition of filler that acts as a reinforcing agent. Tensile toughness, strains at break, and Young's modulus increased with increasing filler content. The viscoelastic behavior of the silicone composites was evaluated in five cyclic stress-strain tests. All materials showed relatively large hysteresis loops for the first cycle due to Mullin's effect, while the subsequent hysteresis became smaller from the second cycle. The composites showed dielectric behavior with low loss (<10−1), relative permittivity superior to pure siloxane (4–5 vs. 3.4), and slightly increased electrical breakdown strength (30–36 V/μm vs. 27 V/μm). The applicative potential of these composites in electromechanical devices was estimated by calculated figures of merit, based on mechanical and dielectric parameters, which indicate their suitability for energy harvesting/capacitive sensors rather than for actuators. In addition, the composite with the highest ε′ was tested as capacitive pressure sensor, showing a high sensitivity at low pressure, with potential application in wearable devices. [Display omitted] • A PDMS-α,ω-diol is engineered for application in dielectric elastomer transducers. • Octacarboxy-functionalized POSS is used as active filler for silicone. • Mechanical, thermal properties, dielectric permittivity and strength are improved. • High sensitivity at low pressure indicates potential application in wearable devices. • Calculations indicate the composite more suitable for dielectric elastomer generator. [ABSTRACT FROM AUTHOR]

Polar-nonpolar silicone materials of different morphology and composition were investigated by means of broadband dielectric relaxation spectroscopy in order to elucidate the effect of polar content and nature of the interface on the segmental mobility of polydimethylsiloxane (PDMS) chains. The variation of dielectric parameters with temperature revealed two distinct α-relaxations corresponding to dynamic glass transitions of the components, while another polarization phenomenon was evidenced due to accumulations of charges at the interphases between the two polymers with different electrical properties. It was found that the secondary β-relaxation was favored by the increased content of polar groups, while this parameter had the reverse influence on both α PDMS and α P62 , restricting the PDMS chain segment mobility. The activation energy of the interfacial polarization decreased with the polarity, showing increased mobility of charge carriers and less restriction to the interfacial polarization. [ABSTRACT FROM AUTHOR]

A series of elastomers, either natural or synthetic (some of them commercial, while others prepared in the laboratory), suitable for use as active elements in devices for wave energy harvesting, were evaluated concerning their behavior and effects on the marine environment. In this aim, the elastomer films, initially evaluated regarding their aspect, structure, surface wettability, and tolerance of microorganisms growth, were immersed in synthetic seawater (SSW) within six months for assessing compounds released. There were analyzed the changes occurred both in the elastomers and salt water in which they were immersed. For this, water samples taken at set time intervals were analyzed by using a sequence of sensitive spectral techniques: UV–vis, IR, and in relevant cases 1 H NMR and electrospray ionization mass spectrometry (ESI–MS), able to detect and identify organic compounds, while after six months, they were also investigated from the point of view of aspect, presence of metal traces, pH, and biological activity. The changes in aspect, structure and morphology of the dielectric films at the end of the dipping period were also evaluated by visual inspection, IR spectroscopy by using spectral subtraction method, and SEM-EDX technique. [ABSTRACT FROM AUTHOR]

Dielectric silicone elastomers able to respond to an electrical stimulus by a mechanical displacement are prepared through a simple one-pot procedure consisting in cross-linking and simultaneous in situ generation of the filler functionalized with polar groups, as reinforcing and dielectric permittivity enhancer. One and the same reagent, (3-chloropropyl)trimethoxysilane (CPTMS), serves as both cross-linker and precursor for the filler. This is incorporated in different amounts with dibutyltindilaurate (DBTDL) into polydimethylsiloxane-α,ω-diols having molecular masses of 34,500 and 125,000 g ⋅ mol − 1 and left for curing in atmospheric conditions. The Fourier Transform Infrared (FTIR) spectra show absorption bands characteristic for silsesquioxane (SSQ) structures formed by converting excess CPTMS, while the Transmission Electron Microscopy (TEM) images reveal biphasic morphology of the resulting material in which formations which we have assumed to be SSQ are distributed within the silicone matrix. The structural aspects and supramolecular organization are investigated by Wide Angle X-Ray Diffraction (WAXD) and Small Angle X-ray Scattering (SAXS) analysis. The influence of the CPTMS amount over the mechanical and dielectric properties of the resulted materials are investigated expecting an improvement of the dielectric permittivity but also a strengthening of material. Lateral strain as a response to an applied voltage on dielectric films is measured. [ABSTRACT FROM AUTHOR]

The first cyclic ferrocenylsiloxane-urea, {1,1′-ferrocene-diurea-[1,3-bis(propylene)tetramethyldisiloxane]} (FSU), has been formed by reacting 1,1′-ferrocenediisocyanate with 1,3-bis(aminopropyl)-tetramethyldisiloxane in a chloroform–toluene mixture. The ferrocenylsiloxane urea was structurally characterized by FTIR and 1 H NMR spectroscopy, elemental analysis, mass spectrometry (ESI-MS), and single crystal X-ray diffraction. The electrochemical behavior was studied by cyclic voltammetry. FSU exhibited one reversible redox wave with a redox coupling E 1/2 = 0.107 V (FSU-CHCl 3 ), and 0.158 V (FSU-DMSO). The 1 H NMR analysis revealed that the ferrocenylsiloxane urea presents association capacity in chloroform, behavior sustained by transmission electron microscopy. The temperature dependence of the hydrogen bonds in the solid state complex was investigated by IR-spectroscopy. [ABSTRACT FROM AUTHOR]

A ceramic material consisting in a zirconium dioxide-lead zirconate mixture has been obtained by precipitation method, its composition being proved by wide angle X-ray powder diffraction and energy-dispersive X-ray spectroscopy. The average diameter of the ceramic particles ranged between 50 and 100 nm, as revealed by transmission electron microscopy images. These were surface treated and used as filler for a high molecular mass polydimethylsiloxane-α,ω-diol (Mn = 450,000) prepared in laboratory, the resulted composites being further processed as films and crosslinked. A condensation procedure, unusual for polydimethylsiloxane having such high molecular mass, with a trifunctional silane was approached for the crosslinking. The effect of filler content on electrical and mechanical properties of the resulted materials was studied and it was found that the dielectric permittivity of nanocomposites increased in line with the concentration of ceramic nanoparticles. [ABSTRACT FROM AUTHOR]

Mixed silicone interpenetrating networks have been prepared using two groups of siloxane polymers and copolymers as precursors in different combinations. Each combination chosen, after a good mixing in solution with cross-linking agents was processed into film, which has been stabilized through sequential crosslinking using separate chemical pathways: condensation with tetraethyl orthosilicate at room temperature for the first network and addition (hydrosilylation) at higher temperatures in the case of the second one. The morphology of the resulted materials was studied by scanning electron microscopy (SEM). The mixing degrees of the two networks were estimated on the basis of the differential scanning calorimetry (DSC) traces as well as by small angle X-ray scattering (SAXS). The obtained films were characterized from point of view of the properties of interest for electromechanical applications by mechanical testing, dielectric spectroscopy and electrical breakdown measurements. The influence of the nature and content of the polar groups attached on the silicon on these characteristics was discussed. [ABSTRACT FROM AUTHOR]

Abstract: The new dicarboxylic acid, 1,3-bis(p-carboxyphenylene-ester-methylene)tetramethyldisiloxane (H2L, 1) was obtained by treating 1,3-bis(chloromethyl)-1,1,3,3-tetramethyldisiloxane with a mixture of terephthalic acid and terephthalic acid sodium salt in a 1:1 ratio. In this approach, besides the desired compound 1 (33 wt % yield), the condensation cyclic dimer 2 (7 wt % yield) and an oligomer 3 (10 wt % yield) resulted. The reaction between dicarboxylic acid H2L, where L is the carboxylate ligand, along with imidazole as co-ligand, and copper hydroxide resulted in the formation of a coordination compound [Cu(HIm)4(H2O)2]L·4.5H2O (4). Single-crystal X-ray crystallography has revealed that the crystal structure of 4 is a self-assembled H-bonded three-dimensional supramolecular structure. FTIR and NMR spectral techniques were also used to characterize the formed structures. Optical and thermal properties of all compounds were studied. The stability of the supramolecular structure in solution (methanol) and with temperature was studied using ATR-FTIR. The ability of the macrocycle 2 to bind potassium cations in solution was investigated by UV–vis spectrophotometry. [Copyright &y& Elsevier]