Poly Methylphenylsiloxane Research Articles

Assay of glyceryl trinitrate, isosorbide dinitrate, and their metabolites in plasma by large‐bore capillary column gas‐liquid chromatography

Two large-bore capillary columns, one with dimethyl polysiloxane (HP-1) as the stationary phase and the other with phenyl (50 per cent) methyl (50 per cent) polysiloxane (DB-17), were used to develop gas-liquid chromatographic (GLC) assays for measuring isosorbide dinitrate (ISDN), glyceryl trinitrate (GTN), and their metabolites. ISDN, isosorbide-2-mononitrate (2-ISMN), and isosorbide-5-mononitrate (5-ISMN) in plasma, ranging in concentration from 1 to 300 nM, and GTN, glyceryl-1,2-dinitrate (1,2-GDN), and glyceryl-1,3-dinitrate (1,3-GDN), ranging in concentration from 3 to 60 nM in plasma, were analysed on both columns. GLC analysis yielded baseline resolution of the analytes. The method using the dimethyl polysiloxane column gave a lower limit of detectability for GTN of 0.75 nM (signal/noise (s/n) = 2), and the procedure using the phenyl-methyl column provided a lower limit of detectability for ISDN of 81 pM (s/n = 2). The large-bore column GLC procedures exhibited shorter retention times for both ISDN and GTN than those previously reported for capillary-column assays. The chromatographic resolution of analytes and column efficiency of the large-bore capillary columns were comparable to the results previously found using capillary-column GC. The assays for ISDN and GTN have been shown to be appropriate for pharmacokinetic studies in volunteers and patients. We determined that the HP-1 column is appropriate for the analysis of GTN and metabolites, and the DB-17 column is suitable for analysis of ISDN and its metabolites. We conclude that the use of large-bore capillary columns provides rapid and reliable GLC assays for organic nitrates.

Shear rheology in a confined geometry: polysiloxane melts

The dynamic mechanical shear response was measured of sharp fractions of molten siloxane oligomers, PDMS ( poly(dimethylsiloxane)) and PPMS ( poly(phenylmethylsiloxane)), confined between single crystals of muscovite mica, at film thicknesses e100 A and a temperature of 23 C. Five conclusions emerge. (1) A liquidlike mechanical response (in which the apparent dynamic viscosity was significantly enhanced over that of the bulk liquid) was clearly distinguished from a yield stress response (in which sliding over the experimental time scale occurred only after a critical yield stress was exceeded). These same features were observed previously for ultrathin films of smaller nonpolar molecules, and, despite quantitative differences in the present systems, the observation appears to be general. (2) The precise film thickness at the onset of the yield stress response, observed at film thicknesses C30-50 A, did not depend on the molecular weight of the PDMS fractions but did depend markedly on details of the history of the experiment. (3) The yield stress increased with measurement time without a discernible change in separation. The times for the yield stress to reach a plateau increased with molecular weight and ranged from approximately 9 min (PDMS, Mn = 890) to approximately 400 min (PDMS, Mn = 6330) and approximately 650 min (PPMS, M, = 2240). (4) Enhanced viscous response was observed at larger film thickness than for liquids of smaller molecules. The distance dependence of the apparent dynamic viscwity at 0.875 Hz was quantified for one sample (PDMS, M, = 1670) by measuring the phase shift and amplitude attenuation in sinusoidal oscillation. The apparent dynamic viscosity appeared to diverge with diminishing film thickness. (5) After discussing how the act of shear may affect the structure of the liquid, we conclude that the yield stress rheological response may reflect a metastable, history-dependent state, in which relaxations of trapped chains have become slower than the experimental time scale of minutes to hours.

Capillary supercritical fluid chromatography of aliphatic amines : Studies on the selectivity and symmetry with three different columns using carbon dioxide or nitrous oxide as mobile phase

The supercritical fluid chromatography of intact aliphatic amines with different columns is described. One group of amines was based on N,N-dimethyl- n-octylamine and related primary and secondary amines, and the other on the amino alcohol metoprolol and several of its analogues. Columns with three different phases were investigated, one non-polar coated with 5% phenyl methyl polysiloxane and two more polar with 25% cyanopropyl methylphenyl polysiloxane and Carbowax 20M. Generally, equal molar amounts were injected under splitless conditions and the peak symmetry was recorded. The system with the non-polar silicone phase was more inert, followed by the wax-phase column. The cyanopropyl column gave severe peak tailing although it was loaded with five times more of the amines than the other columns. The selectivity was investigated and was found higher with the two polar columns. Both showed a marked increase in the retention of amines with free hydrogens. With nitrous oxide the selectivity was almost the same as that with carbon dioxide as mobile phase. The nature of the flame ionization detector changed, however, giving a negative baseline drift on pressure programming. An interesting conclusion is that the amines are chromatographed as such with carbon dioxide as the mobile phase.

Polysiloxane: potential noncaloric fat substitute; effects on body composition of obese Zucker rats

Phenylmethylpolysiloxane (PS), a noncaloric, nonabsorbable liquid oil, was studied for effects on body comparison as fat substitute in the diet. Two groups of female obese Zucker rats were fed either a control low-fat (LF) or an experimental diet containing PS (22% wt/wt) incorporated into LF. Two additional groups were fed either PS or cellulose (CE) in diet providing equivalent caloric dilution. Rats on PS lost weight whereas LF control rats gained. Dissectible fat and adipocyte size of PS were smaller than those of LF. Food intake, body water, and adipocyte number did not differ between PS and LF. Body protein on PS increased only in proportion to weight. When both diets were diluted, PS animals lost more weight than CE controls despite similar food intakes, suggesting absorption of calorigenic substances derived from partial digestion of CE but not PS by intestinal microflora. Obese rats did not compensate for caloric dilution with PS.

Development of a 69kV High-Pressure Gas-Filled Pipe-Type Cable System for an Arctic Environment

A high-pressure gas-filled (HPGF) pipe-type cable system rated 69kV has been developed for operation at Prudhoe Bay, Alaska, which is at the North Slope above the Arctic Circle. A minimum ground ambient of -10°C is applicable to the major portion of the circuit which is buried. The cables installed in pipes across a 46 m (150 foot) long bridge, the terminal riser cables and the cable terminals experience a minimum air ambient of -48°C. The cable design for each of these ambient temperatures required special consideration with regard to the insulation structure and impregnant to be employed for the paper insulation. This paper describes the investigation of materials, cable models and prototype cables to achieve the physical and electrical properties required for the application. For the buried cable, a polybutene impregnant having a viscosity lower than normally employed for HPGF cable was used. For the cables exposed to the lower ambient air temperature, a phenylmethyl polysiloxane silicone fluid was selected as the impregnant. A transition joint between the polybutene and silicone impregnated cables was developed. Standard gas-filled terminals were modified for service at the low ambient air temperature. The successful completion of this R&D project has provided a rugged, reliable high voltage cable system suitable for transmitting power in an arctic environment.

Application of capillary supercritical fluid chromatography to the analysis of a middle distillate fuel

The application of capillary supercritical fluid chromatography (SFC) to the analysis of a middle distillate fuel is described. Small diameter (50μm i.d.) fused-silica capillary columns coated with crosslinked 50% phenyl polymethylphenyl siloxane provided high separation efficiency and good compatibility with flame ionization detection. High resolution separations of the chemical class fractions obtained by adsorption chromatography on alumina were obtained using carbon dioxide as the supercritical mobile phase and simple pressure programming techniques. In addition to the less polar fuel components, supercritical carbon dioxide allowed chromatography of the nitrogen-containing polycyclic aromatic hydrocarbon fraction and the hydroxylated polycyclic aromatic materials.

Multiple and Bonded Phases in Open-Tubular Column Gas Chromatography. Blended Dimethyl and Methylphenyl Polysiloxane Solvents

Retention de dix solutes (hydrocarbures satures et benzeniques) sur les phases OV-101, OV-3, OV-7, OV-11, OV-17, OV-22, OV-25

Dielectric relaxation and effect of plasticisers on siloxane polymers

Studies of dielectric relaxation of polydimethyl siloxane have shown that there is anomalous behaviour near its melting point (≈ −50°), probably due to the presence of “Rotator Phases”. A detailed study of polyphenyl methyl siloxane, with various polar and non-polar diluents, has been carried out. The most interesting aspect of this study is the systematic broadening of the loss curves with increasing concentration of diluents while retaining conformity with the empirical decay function π( t) = exp − ( t/ τ o ) β . The broadening of loss curves was explained in terms of a distribution of local concentration of the diluents. The range of concentration ( ΔC) was calculated for various diluents. It was found that ΔC was larger for the polar diluents than for the non-polar diluents. This result shows that polar plasticiser molecules have changed considerably the environment of the segmental motion of the basic polymer. There is also a linear relationship between the loss factor maximum ( ϵ ″ m ) with the number of carbon atoms in the plasticiser molecule.

Depolarized Rayleigh spectra of siloxane polymers

We report measurements of depolarized Rayleigh spectra IVH(ω) of polyphenylmethyl siloxane (polymer A) in bulk and in carbon tetrachloride, of polydimethylphenylmethyl siloxane (copolymer B) in bulk, and of depolarized Rayleigh intensity IVH of polydiphenyl siloxane in carbon tetrachloride. From the temperature dependence and the concentration dependence of IVH, we were able to determine positive intermolecular and intramolecular static pair correlations of polymer A and of copolymer B, and negative intermolecular and intramolecular static pair correlation of polydiphenyl siloxane solutions. The results are explained in terms of the most preferred orientation of phenyl groups attached to the polymer backbone. The linewidths of depolarized Rayleigh spectra of polymer A and of copolymer B can be attributed as due to the crankshaft type of motion of the polymer backbone which orients the polarizability anisotropy of the phenyl groups. The local reorientation time is virtually independent of the macroscopic viscosity. The apparent activation energy (∼2.3 kcal/mol) is much lower than that determined by the dielectric relaxation technique but is of the same order as that calculated from Brillouin spectra.

Rayleigh–Brillouin spectra of polymer fluids: Polyphenylmethyl siloxane and polydimethylphenylmethyl siloxane

Measurements of Rayleigh–Brillouin spectra of polyphenylmethyl siloxane (A) and of polydimethylphenylmethyl siloxane (B) over a wide range of temperatures (270 to 520 K for A; 280 to 390 K for B) are reported. By using the generalized hydrodynamic theory for Rayleigh–Brillouin spectra as developed by Lin and Wang, we have determined the relaxation strength R, the relaxation rate t, the activation energy Ea, and the adiabatic sound frequency ws (T), which are the characteristic physical quantities describing the dynamics of a viscoelastic polymer fluid in the GHz region. Based on those parameters, we were able to obtain excellent agreement between the theoretical and the measured spectra.

Synthesis and properties of star-shaped polymethylphenyl siloxane

A study was made of joint interaction of cis-1,3,5-trimethyl-1,3,5, triphenyl-cyclotrisiloxane and tetrakis-(3,5,7-trimethyl-3,5,7-triphenyltrisiloxane-7-hydroxy) titanium or silane in the presence of potassium trimethylsilanolate in bulk at 105° and it was shown that this interaction may take place to obtain polymethylphenylsiloxanes with star-shaped macromolecules.

Glass open-tubular capillary columns with chemically bonded methyl-phenyl siloxane stationary phases of tailor made polarity

The previously described method yielding apolar, chemically bonded methyl polysiloxane glass capillary columns was extended to the production of capillary systems of controlled polarity. The approach involved prior synthesis of a reactive methyl-phenyl polysiloxane polymer by copolymerisation of a mixture of dimethyl and diphenyl chlorosilanes. The polymer was then chemically bonded to the capillary glass surface to yield remarkably stable, high resolution analytical systems which were shown to be particularly well suited to the separation of biochemical mixtures at the subnanogram level. The principle of copolymerisation of differently substituted silanes confers to the method a considerable flexibility which could be used to devise polar capillary systems tailor made for a given analytical problem.

Spin-lattice relaxation in substituted polysiloxanes

Spin-lattice relaxation time ( T 1) measurements have been made over wide ranges of temperature for polydimethylsiloxane (DMS), polyphenylmethylsiloxane (PMS) and poly(3,3,3-trifluoropropylmethylsiloxane) (FMS) gums and an FMS oil. For all polymers two T 1 minima were observed. Activation energies E t 1 , of DMS, PMS and FMS were obtained for the high temperature process reflecting the effect of the bulky substituents on the segmental motion. T 1 measurements were also made over a wide range of dilution for the same polymers in several solvents. For DMS both T 1 and E t 1 were little affected by dilution over a wide range. For PMS and FMS, T 1 increased steadily and E t 1 decreased on dilution. Long range (intersegmental) interactions do not appear to play a dominant role in the change of T 1 with concentration.

GC-MS Characterization of the Compounds in Some Essential Oils

The composition of different essential oils (menthe, basil, lavender, rose) was investigated by gas chromatographic–mass spectrometry (GC–MS) method to identify those compounds responsible for the characteristic, pleasant floral or aroma odour or taste of some valuable oils. Three different rose oils presented monoterpenes as fragrance target compounds and some aliphatic hydrocarbons with fixative effects responsible for a longer-lasting odour impression. Chromatography was performed on a 5% phenyl methylpolysiloxane column (15 or 30 m x 0.25 mm I.D., 0.25 µm) operated in suitable temperature programs.

A lipid-soluble inert indicator in fat absorption studies in the rat.

Abstract Lipid-soluble DC Silicone Fluid 703 (a methyl-phenyl polysiloxane) was tested as an inert indicator in fat absorption studies. The recovery of this fluid in rat stools was 96.0 ± 6.7 per cent (mean ± S.D.). This agreed with the recovery in the in vitro experiment, 93.8 ± 4.0 per cent, where known amounts of DC Silicone Fluid 703 were added to rat feces and analyzed. In the amounts tested (75, 150, and 300 mg.), DC Silicone Fluid 703 had no influence on the absorption of glyceryl-tristearate-1-C 14 in olive oil. The absorption of this mixture determined by the aid of DC Silicone Fluid 703 as an inert indicator and by the complete collection of the stool was 88.8 ± 3.0 per cent and 89.2 ± 3.6 per cent, respectively. From these results DC Silicone Fluid 703 was considered to be a suitable inert indicator for use in fat absorption studies.

Quantum efficiency of the 2537 A. Photolysis of a mixed phenyl–methyl polysiloxane

AbstractThe ultraviolet (λ = 2537 A.) photolysis of a degassed mixed phenyl and methyl polysiloxane liquid is examined in terms of gas and crosslinking yields. Results are compared to the published values obtained by ionizing irradiation of this type of molecule. It is shown that ultraviolet radiation is less efficient by two orders of magnitude in producing decomposition (i.e., gaseous products) than is ionizing radiation. The comparisons for crosslinking efficiencies are less certain, but the yields seem to have much more similar values in this case based on a spectroscopic estimation of crosslinking (i.e., analysis for substituted phenylcyclohexadiene formation). The gas quantum yields were ϕH2 = 2.6 × 10−5, ϕCH4 = 0.63 × 10−5, ϕC2H6 ≈ 0.12 × 10−5, and ϕC2H2 ≈ 0.06 × 10−5.

The failure of absorption of DC silicone fluid 703 from the gastrointestinal tract of rats.

The intestinal absorption of silicone fluid 703, a methyl phenyl polysiloxane, has been studied in the rat. This silicone was chosen for the present investigation because of its lipid-like character and its solubility in olive oil. The experimental findings demonstrate that very little, if any, silicone is absorbed when fed in olive oil. No silicone was found in the lymph lipids of cannulated rats fed the silicone, and balance experiments by recovery of the organosilicon compound and triglyceride after feeding to rats for three hours showed that 85% of silicone fluid 703 was recovered from the gastrointestinal tract, whereas 70% of the fed triglyceride was absorbed. The unabsorbed silicone was concentrated chiefly in the intestinal lumen. Balance experiments by recovery of the organosilicon compound after long-term feeding gave recoveries of 96% of the silicone. This amount was recovered entirely from the lower part of the gastrointestinal tract and the faeces. No silicon fluid 703 was found in the liver, kidneys, or fat depots. The urine contained no soluble silica.