synopsisDilute solution parameters were determined for polymethylphenylsiloxamer fractions (5 X lo* < M < 1.5 X 108) in toluene, cyclohexane, and diisobutylamine (e = 30.4OC).The data are interpreted by the procedure suggested by Flory and Fox. Minor deviations from theory are noted. Polymers from both &-and trans-cyclotrisiloxanw were investigated. The major portion of the work, however, was concentrated on fractions derived from the trans form. From the data obtained, a characteristic ratio of dimensions (G2/rTf2)'/z of 1.56 was determined. The hydrodynamic parameter was determined to be (2.0 + 0.3) X 1021. The appropriat,e model for the polymer is indicated to be the impermeable random coil with slight hindrance to rotation about backbone skeletal bonds.
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Solution parameters for the polymer poly‐γ‐trifluoro‐propylmethylsiloxamer has been determined in cyclohexyl acetate, methyl hexanoate, and ethyl acetate. Interpretation of data follows the theory of Fox and Flory. In contrast to poly‐dimethylsiloxane, an increased steric hindrance to rotation about the siloxane bond occurs as evidenced by the characteristic ratio of root‐mean‐square end to end dimensions, (r02/r0f2)1/2, found to be 1.90 and 1.96 at 25.0 and 72.8°C, respectively. This increase is considered to be primarily due to nearest‐neighbor interaction of the polar substituent on the silicon atom. The relation, [η]θ ∝ M1/2, was observed to hold for this polymer system. The hydrodynamic model appropriate for the polymer is a random coil considerably more permeable to solvent flow than is generally reported for linear polymers. The universal parameter ϕ was determined to be 1.5 × 1021. The effect of temperature on polymer configuration is indicated to be negligible.
Two independent methods, using gas chromatography (GC) and high performance liquid chromatography (HPLC), have been developed for the determination of polychlorinated biphenyls (PCB) in polydimethylsiloxane (PDMS) fluids. For low levels (<5 ppm) of PCB, charcoal column chromatography Is used to separate the PCB from the siloxane matrix for subsequent GC analysis. At higher levels, the sample may be diluted In hexane and analyzed directly by gas chromatography with electron capture detection. For HPLC with UV detection, the PCB are separated from the siloxane by an acetonitrile extraction and analyzed by reverse-phase chromatography. The GC method is preferred for low concentrations of PCB. HPLC is often convenient for higher PCB levels or when trichlorobenzene concentrations are to be determined. The lower detection limit for PCB by GC is 25 ppb (wt/wt). The lower detection limit for PCB by HPLC is 100 ppb. If interfering species are present, the detection limits may be higher.
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