Linear Polydimethylsiloxane Research Articles

Phase separation induced macroporous SiOC ceramics derived from polysiloxane

Abstract Macroporous SiOC ceramics have been fabricated through crosslinking and pyrolysis of a two-component polysiloxane (PSO) precursor consisting polyhydrosiloxane (PHMS) and tetravinylcycletetrasiloxane (D4Vi) utilizing phase separation of linear polydimethylsiloxane (PDMS) in PSO. The crosslinking of PSO is initiated by Pt-catalyzed hydrosilylation between PHMS and D4Vi concurrently; and at the meantime phase separation also occurs, forming PSO-rich and PDMS-rich phases. The morphology of PDMS phase in the obtained PSO/PDMS gel can be easily tailored from isolated phase to continuous phase by tuning the initial PDMS concentration. Subsequent pyrolysis treatment yields macroporous SiOC ceramics in which pores arise from thermal depolymerization and evaporation of the PDMS phase. The obtained SiOC ceramics possess controllable morphologies with closed-pores structure, worm-like continuous structure or stacking-particulates structure, which perfectly resembles the morphology of respective PSO/PDMS gel.

Novel supramolecular elastomer films based on linear carboxyl-terminated polydimethylsiloxane oligomers: preparation, characterization, biocompatibility, and application in wound dressings

A novel supramolecular elastomer (SESi) based on multiple hydrogen bond associations between low-molecular-weight polydimethylsiloxane chains was obtained through a two-step reaction of linear carboxyl-terminated polydimethylsiloxane oligomers with diethylenetriamine and urea, and the reaction mechanism was characterized. The results of differential scanning calorimetry and X-ray diffraction analyses indicated that the supramolecular network structure is completely amorphous, endowing SESi with rubber-like elastic behavior at room temperature. The transparent SESi film prepared by hot pressing displayed nice viscoelasticity, benign water absorption, water vapor transition rates, and ideal biocompatibility; and did not show cytotoxicity or skin irritation. These properties allow the elastomer to function as an occlusive wound dressing. To demonstrate its potential in wound dressings, a detailed comparison of commercial 3M Tegaderm™ film and the SESi film was conducted. The SESi film exhibited similar effects in wound healing, and the wound bed was covered by the SESi film without the occurrence of significant adverse reactions.

Drill fluid selection for the SUBGLACIOR probe: a review of silicone oil as a drill fluid

AbstractAs part of the ICE&LASER/SUBGLACIOR projects, an innovative probe called SUBGLACIOR is developed with the aim of perforating the ice sheet down to depths of 3500 m in a single season and continuously measuring in situ the isotopic composition of the meltwater and the methane concentration in trapped gases. Ice chips generated by the electromechanical drilling will be removed from the borehole by circulating a drill fluid. The selection of this drill fluid is important as it will have a major impact on the performance and the environmental evaluation. A literature review of drilling liquids is carried out to select potential fluids for further detailed testing. The selected fluids are varying grades of silicone oils, known as linear polydimethylsiloxanes, and ESTISOL™ 140, an aliphatic ester. The requirements for this project are similar to those for other deep ice-core drilling projects but, due to the embedded analytical system and the speed of drilling, there are some specific considerations. Following extensive testing, we conclude that a silicone fluid with a kinematic viscosity of 3 mm2 s−1 (3 cSt) is ideally suitable and affordable. This evaluation provides new insights into the use of silicone oils as a drill fluid that are of use to the wider ice-core drilling community.

Preparation and characterization of looped polydimethylsiloxane brushes

We have synthesized and characterized a looped polymer that is covalently bonded to a surface at both chain termini. We used the ‘grafting to’ method to anchor polydimethylsiloxane (PDMS) onto a Si substrate by making use of triethoxysilyl terminal units. Atomic force microscopy revealed that a linear polymer brush provides a rough surface in water. As water is a poor solvent for PDMS, linear polymer brushes tend to be dewetted, forming aggregates. In contrast, a looped polymer brush surface is smooth in air and water. Aggregation was suppressed in the looped polymer brushes because both ends were tethered to the surface. As surface characteristics, the looped polymer brushes shows low water contact angle hysteresis and low sliding angle. Technologically useful surface properties are provided on the surface by the PDMS coatings. Both looped and linear polydimethylsiloxane (PDMS) polymer brushes were fabricated onto a Si substrate using the ‘grafting to’ method. As water is a poor solvent for PDMS, linear polymer brushes tended to be dewetted in water, forming aggregates. Therefore, a linear polymer brush showed a rough surface in water. In contrast, a looped polymer brush surface was smooth even in water. Aggregation was suppressed because both ends were tethered to the surface.

<I>In-Situ</I> Compatibilization of Linear Low-Density Polyethylene and Polydimethyl Siloxane Rubber Through Reactive Blending

<I>In-Situ</I> Compatibilization of Linear Low-Density Polyethylene and Polydimethyl Siloxane Rubber Through Reactive Blending

Effect of die geometry on helical defect during extrusion of PDMS across a radial flow upstream the contraction

The present work aims at analyzing the influence of both die geometry and entry flow on the appearance and the evolution of the helical defect. The experiments have been performed with linear polydimethylsiloxane (PDMS) via a capillary rheometer in which a convergent radial flow was created upstream the contraction. For a small gap width of radial flow, it was demonstrated that the decrease of the die length-to-die diameter ratio allows the reduction of the helical defect. Moreover, with a short die, when the gap width-to-die diameter ratio is reduced, the helical defect is lessened. In fact, compared to the average diameter of extrudate, the helix pitch and the distortion amplitude are reduced when the die is of a small length and a large diameter as well as the radial flow is of a small gap width.

Influence of PDMS chain length on proton conductivity in polysiloxane based membranes for HT-PEMFC application

Siloxane based membranes were produced with benzimidazole as proton conducting group by cross-linking siloxane monomers with two or three cross-linking groups. The network structure was further modified by adding a constant amount of silanol terminated linear polydimethylsiloxanes (PDMS) with varying chain lengths. Their influence on glass transition temperature, network formation and proton conductivity at varying relative humidities was investigated at temperatures from 30 to 160 °C. An increasing PDMS chain length decreases the glass transition temperature and changes the hydrophobicity of the membranes. The increase of the number of cross-linking groups leads to additional uncross-linked groups and consequently to a wider network. The new membrane materials possess high proton conductivities of up to 1.2 × 10 −3 S/cm at 160 °C at relative humidities of less than 8% with thermal stabilities of up to 286 °C.

Polysiloxanes With Quaternary Ammonium Salt Biocidal Functions and Their Behavior When Incorporated Into a Silicone Elastomer Network

Polysiloxanes of various structures having biocidal quaternary ammonium salt (QAS) groups pendant to the polymer chain were prepared. Their antibacterial activities were compared in aqueous solution. Selected polysiloxanes were linear polydimethylsiloxanes having 20% siloxane units substituted at silicon by 3(dimethyl-n-octylammonio)propyl chloride or 3(dimethyl-n-hexadecylammonio)propyl chloride and terminated by silanol functions at both chain ends. They were crosslinked and also incorporated by co-crosslinking into an RTV (room temperature vulcanized) silicone elastomer. Bacteriocidal activities of surfaces of the crosslinked biocidal polysiloxanes and of the elastomers having incorporated these polymers were determined by the colony count method. Thousand-fold reduction of Staphylococcus aureus in contact with the dimethyl-n-octylammonio substituted polymer was achieved in 2 min and in contact with the elastomer containing 20 wt% of this polymer in 15 min, although the density of the QAS was as low as 0.36 mmol/g. The surface structure and properties of the elastomers were studied by XPS, contact angle, AFM and model human serum protein (HSA) adsorption. Water sorption by this material was also studied. The concentration of QAS groups on the elastomer surface depended strongly on the material surroundings. No QAS was found on the surface in ultrahigh vacuum, while a strong enhancement of QAS presence on the surface was observed when it was in contact with water or water vapor. Hydrophobicity of the elastomer surface was little affected by the incorporated biocidal QAS-containing polysiloxane when the elastomer was kept in air. This material showed little ability to adsorb the HSA protein from its aqueous solution.

Effect of radial flow in the die entrance region on gross melt fracture of PDMS extrudate

The gross melt fracture defect is related to the flow instabilities developed in the contraction region. To mitigate these upstream instabilities, a convergent radial flow in the die entrance has been created. In fact, the ultimate objective of the present work is to examine the effect of the clearance width of radial flow on the appearance and development of gross melt fracture defect. So, capillary rheometer experiments were performed with linear polydimethylsiloxane (PDMS) oil. As for the influence of radial flow width on the morphology of gross melt fracture defect, extrudate photographs show that this imperfection can be mitigated since its frequency is higher and amplitude smaller when the gap of radial flow decreases. Such results may be related both to shear and elongational components of radial flow. Actually, when gap width is very small compared to the external diameter of radial flow, shear deformations become more enhanced with respect to the elongational deformations and thus the helical gross melt fracture becomes more like a surface defect than volume defect.

A thermosensitive supramolecular aggregation from linear telechelic polydimethylsiloxane with self-assembly units

A new thermosensitive material, polydimethylsiloxane supramolecular aggregation (PDMS-SMA-1), was prepared by coupling the N-pyridin-2-yl-succinamic acid with aminopropyl-terminated polydimethylsiloxane via amidated reaction. Its structure was confirmed by FT-IR, 1H NMR and 13C NMR. And the FT-IR spectra, molecular dynamics simulations and density functional theory calculations supported the existence of intermolecular hydrogen bonding and π-π stacking in supramolecular aggregation and obtained its possible self-assembly structure. A combination of DSC measurements, oscillatory shear experiments, and AFM measurements was carried out to further investigate the nature of PDMS-SMA-1. The results indicated that hydrogen bonding and π-π stacking combined with phase segregation were important for the preparation of thermosensitive materials. Moreover, in order to investigate the effect of molecular weight on the thermal sensitivity and morphology of supramolecular aggregation, PDMS-SMA-2 with higher molecular weight was also synthesized. In contrast to PDMS-SMA-1, it had similar thermal properties but different morphology. All the characteristics of supramolecular aggregation suggested a much wider range of hydrogen bonding and π-π stacking motifs which could be applied in intelligent materials.

Temperature-Dependent Vapor Pressure of Selected Cyclic and Linear Polydimethylsiloxane Oligomers

The isothermal retention times of seven cyclic (D4 to D10) and nine linear (L5 to L13) dimethylsiloxane oligomers on a nonpolar gas chromatographic column were determined at temperatures between (308.15 and 438.15) K. Using normal alkanes as standard reference and calibration compounds, these retention times were used to derive liquid state vapor pressures at 298.15 K as well as enthalpies of vaporization that allow for the estimation of vapor pressures over a wide range of temperatures. The data agree within 0.25 log units with vapor pressure values previously reported by Flaningam (1986) but extend those values to lower temperatures and larger oligomers. Cyclic dimethylsiloxanes are more volatile than linear dimethylsiloxanes of a similar size. Oligomers with 10 and more dimethylsiloxane units are expected to sorb appreciably to aerosol at environmentally relevant temperatures.

Molecular weight changes induced in an anionic polydimethylsiloxane by gamma irradiation in vacuum

An anionic almost monodisperse linear polydimethylsiloxane (PDMS) was subjected to gamma irradiation under vacuum at room temperature. The molecular weight changes induced by the radiation process have been investigated using size exclusion chromatography (SEC) with refraction index (RI) and multi angle laser light scattering (MALLS) detectors, to obtain the number and weight average molecular weights of the irradiated samples. The analysis of the data indicates that crosslinking reactions predominated over scission reactions. The results obtained by an SEC-RI have confirmed the presence of small, but measurable amounts of scission. A previously developed mathematical model of the irradiation process that accounts for simultaneous scission and crosslinking and allows for both H- and Y-crosslinks, fitted well the measured molecular weight data. This prediction is in accordance with the experimental data obtained by 29Si-Nuclear Magnetic Resonance spectroscopy (NMR) and previously reported data for commercial linear PDMS ( Satti et al., 2008).

Polysiloxane Based Membranes for High Temperature Polymer Electrolyte Membrane Fuel Cells (HT-PEMFC)

Membranes with benzimidazole as proton conducting group and siloxanes as backbone were prepared by cross-linking siloxane monomers. The influence of additional amounts of silanol terminated linear polydimethylsiloxane (PDMS) on glass transition temperature and proton conductivity under anhydrous conditions were investigated. The new membrane materials possess high thermal stabilities up to 286{degree sign}C and exhibit proton conductivities up to 2 x 10-4 S/cm at 160{degree sign}C.

Synthesis and characterization of polyurethane hybrids: Influence of the polydimethylsiloxane linear chain and silsesquioxane cubic structure on the thermal and mechanical properties of polyurethane hybrids

AbstractThe structural effects of polydimethylsiloxane (PDMS) or polyhedral oligosilsesquioxanes (POSSs) on the thermomechanical properties of polyurethane (PU) networks were studied. An ester–amine‐functionalized silsesquioxane and a PDMS macromer were synthesized, and the macromer (10 wt %) was crosslinked with the PU prepolymer to obtain PU networks. The synthesized macromers and hybrids were characterized with Fourier transform infrared, 1H‐NMR, 13C‐NMR, and 29Si‐NMR spectroscopy techniques. The influence of POSS cubes on the thermal and mechanical properties of the polymer network films was studied comparatively with the similarly functionalized PDMS linear chain via thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) measurements. The degradation pattern of the POSS‐incorporated PU nanocomposites was almost the same as that of the PU network synthesized from the linear PDMS macromer. The differences in the char yields and activation energies of the hybrids reflected the enhancement of the thermal properties of the nanohybrids. The TGA and DSC curves of the macromers suggested that the thermal properties of the macromers not only depended on either the PDMS or POSS inorganic core but also depended on the organic peripheral attached to the inorganic core. The glass‐transition temperatures of the nanohybrids were higher than those of the linear‐PDMS‐incorporated hybrids. The storage modulus values increased 3‐fold upon the incorporation of POSS rigid groups into the PU hybrids in comparison with the flexible PDMS‐chain‐incorporated PU hybrids. The DMA measurements showed a long‐range rubbery plateau region for all the PU hybrids, with high storage modulus and tan δ values showing the structural homogeneity of the crosslinked networks. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Siloxanes in biogases from landfills and wastewater digesters

Volatile methylsiloxanes and linear polydimethylsiloxanes (siloxanes), generated as components of biogases from digesters at wastewater treatment plants and solid waste landfills, have been identified as potentially causing significant operational problems. The problems are demonstrated as being an issue of “sand in the transmission” and are the reason for the changing of engine warrantees. Examples of monitored concentrations of siloxanes at a series of facilities are described, demonstrating degrees of variability both spatially and temporally, for different biogas sources. Wastewater digesters are shown to be generally producing biogases with higher siloxane concentrations than landfills. With a trend toward some landfills being operated as bioreactors, where the temperatures in the refuse are elevated to levels comparable to those within wastewater treatment digesters, there is potential that landfill-derived biogases may result in increased concentrations of siloxanes and hence more operating problems.

Modelling molecular weight changes induced in polydimethylsiloxane by gamma and electron beam irradiation

A commercial linear polydimethylsiloxane (PDMS) was subject to gamma irradiation under vacuum and in air, as well as to accelerated electron beam radiolysis (EB). All irradiation treatments were done at room temperature. The molecular weight changes induced by the radiation processes have been investigated using size exclusion chromatography (SEC) with refraction index (RI) and multi angle laser light scattering (MALLS) detectors to obtain the number and weight average molecular weights of the irradiated samples.The analysis of the data indicates that crosslinking reactions predominated over scission reactions in all cases. Gamma irradiation under vacuum was the most efficient process within the analyzed dose range, reaching the gel point earlier. Irradiation in the presence of oxygen induces oxidative effects, both in gamma and EB irradiations. A previously developed mathematical model of the irradiation process that accounts for simultaneous scission and crosslinking and allows for both H and Y crosslinks fitted well the measured molecular weight data.

Size exclusion chromatography with evaporative light scattering detection: Method for the determination of polydimethylsiloxanes: II. Application of TSK-GEL H HRGMH HR-M column to determine and separate molecular weight of linear polydimethylsiloxanes

Issues concerned with molecular weight distribution analysis of linear polydimethylsiloxanes have not been extensively investigated and mastered, yet. Current publications do not provide detailed research data on the evaluation of the polymerization degree of polydimethylsiloxanes (PDMS) present in variable matrices: e.g. pharmaceuticals, cosmetics, foodstuffs nor indicate molecular weights of the polymer used. However, the information on molecular weight, i.e. viscosity, is of primary importance as it directly affects PDMS toxicity, absorption and migration in the living organism. The vast majority of currently applied methods prove to be insufficiently specific for PDMS of a particular molecular weight and therefore alternative analytical methods have to be further researched. In this paper the results of determination of molecular weights in linear polydimethylsiloxanes, using size exclusion chromatography with the evaporative light scattering detector are described. The column calibration curve obtained from low-dispersion standard polystyrene of molecular weights ranging 376–2,570,000 Da was used to determine PDMS molecular weights. Precision and accuracy of determination was obtained. For the mobile phase flow-rate of 0.3 ml/min relative standard deviation RSD ranged to 0.45% and the accuracy of measurement amounted to −0.42%, whereas for flow-rate of 1.0 ml/min RSD ranged to 0.38% and accuracy to +2.15%.

Interfacial Friction and Adhesion of Cross-Linked Polymer Thin Films Swollen with Linear Chains

The preparation and interfacial properties of a new type of tethered, thin-film lubricant coating are presented. These coatings are composed of three components: a dense self-assembled monolayer (SAM) underlayer that presents reactive vinyl groups at its surface; a cross-linked polydimethylsiloxane (PDMS) overlayer that is covalently tethered to the SAM; and free, mobile linear PDMS chains dispersed in the network. We investigate the influence of the molecular weight (Ms) and concentration of the free PDMS chains on the structure and equilibrium swelling properties of the cross-linked films. Using a bead-probe lateral force microscopy measurement technique, we also quantify the interfacial friction and adhesion characteristics of surfaces functionalized with these coatings. We find that both the volume fraction and the molecular weight of free PDMS molecules in the coatings influence their interfacial friction and adhesion properties. For example, the addition of short PDMS chains in dry, cross-linked PDMS thin films yields tethered surface coatings with ultralow friction coefficients (mu = 5.2 x 10(-3)). An analysis based on classical lubrication theory suggests that the reduction in friction force produced by free polymer is a consequence of the gradual separation of asperities on opposing surfaces and the consequent substitution of solid-solid friction by viscous drag of the free polymer chains in the network.

THERMAL DEGRADATION OF IMIDE-CONTAINING SILOXANE-URETHANE COPOLYMER

Two scries of copolymers, siloxane-urethane and imide-containing siloxane-urethane copolymers (SiU and SiUI copolymers), were synthesized from 4,4'-diphenylmethane diisocyanate (MDI), OH-terminated polydimethylsiloxane (PDMS) and chain extender 1,4-butanediol (1,4-BD) or pyromellitic dianhydride (PMDA) in one-step process. SiU copolymer had four stages of degradation. The degradation in the first, second, third and fourth stage were caused by the decomposition of urethane resulted from MDI and 1,4-BD at 250∼320 °C, urethane resulted from MDI and PDMS at 320∼420 °C, linear PDMS at 420∼550 °C, and macro-cyclics PDMS at 550∼620 °C, respectively. SiUI copolymer had three stages of degradation caused by decomposition of urethane resulted from MDI and PDMS, linear PDMS, and PMDA. The imide group and content greatly affected the degradation behavior of copolymer. The influence of components, hard and soft contents on degradation characterization and thermal stability of copolymer at 220 °C and 450 °C were investigated by the isothermal degradation measurements.

Problematyka zwiazana z niektorymi kierunkami zastosowania polidimetylosiloksanow oraz mozliwosci analizy tych zwiazkow

The fields of polydimethylsiloxanes (PDMS) applications for food contact and in pharmaceuticals were presented. An importance of a choice of the proper only linear PDMS characterized with the appropriate polymerization degree, as only permissible according to the regulations being in force, was stressed. Speciation analysis and analytical methods (limit of detection and specificity, Scheme I, Table 1 and 2), allowing the proper differentiation of the substances studied, were discussed. Especially the method of liquid chromatography with laser light scattering detector (LLSD) applied was considered. It should fulfill the best the requirements of analysis of PDMS discussed.