Dimethylsiloxane polymers determination

Gas chromatography has been applied437 to the determination of the low-molecular-weight portion in poly(dimethylsiloxane). Polymers of molecular weight up to 700 in poly(dimethylsiloxane) can be determined on a column packed with OV-1 on Chromosorb W AW-HP with helium as carrier gas and a flame ionisation detector. 

Comparison of the specific retention volumes of hydrocarbons on poly-dimethylsiloxane [10], determined in two different laboratories by two groups of researchers over the temperature range 25—55°C differ by 3—5%. Similarly the determination of retention of n-decane and n-do-decane on linear polyethylene differs by 8% [11,12]. Braun et al. [12] determined the amount of polymer remaining after calcination and found that the support loses 0.2% of weight on drying and 0.46% on calcination. The application of corrections to the results obtained in reference [11] has improved the agreement however the discrepancy depends on the content of stationary phase for 5—6% stationary phase the difference is 7.5%, while for 10—11% it drops to 3.6%. The value determined for the content of stationary phase depends on the method, and so does the value of Vg Table 2.3 shows the difference between the concentra-... 

Combined SEC-MALDI. Mark-Houwinkr-Sakurada (MHS) Parameters As mentioned earlier, combination of the quantitatively reliable LC techniques with the identification power of MS was used to overcome the limitations inherent in the use of either LC or MS alone. In addition to ESI-MS/SEC, combined applications already mentioned, several approaches to SEC/ MALDI time-of-flight (TOF) MS coupling have also been reported [78-83]. In the case of polydisperse polymers, determination of molecular mass by SEC/MALDI-TOF involves the fractionation of the samples through an analytical SEC. Selected fractions are then analyzed by MALDI-TOF and the mass spectra of these nearly monodisperse samples allow the determination of the MWD moments. Montaudo et al. [81] have tested the reliability of the method for different polydisperse samples, such as poly(methylmethacrylate) (PMMA), poly(dimethylsiloxane) (PDMS), and copolyesters. 

Allen et al. (1960) used ultraviolet spectrometry to determine phase compositions in a polymer-polymer-solvent system containing polystyrene and polyisobutylene. At a wavelength of 250-260 nm, polystyrene has a strong adsorption band, which is linearly related to concentration, while polyisobutylene is transparent. Similarly, for a system containing polydimethylsiloxane and polyisobutylene, they used infrared spectrometry because poly-dimethylsiloxane absorbs at 1261 cm 1 and polyisobutylene is transparent at this wavelength. UVS and IRS have been used with other systems which contain only one polymer which has a strong adsorption band. 

Ashworth, A. J. Price, G. J., "Static Investigation of the Influence of Polymer Molecular Weight and Loading in the Gas Chromatographic Determination of Poly(dimethylsiloxane) Interaction Parameters," Macromolecules, 19, 358 (1986). 

Synthesis. Synthesis of the copolymers was performed by a hydrosilylation reaction of poly(dimethylsiloxane-co-methylhydrosiloxane) (Petrarch System, Inc.) and a-olefins of various lengths (Aldrich). A round-bottomed flask equipped with a magnetic stirring bar, condenser, and calcium chloride tube was charged with a 50% solution of the reactants (up to 10% molar excess of a-olefin) in dry toluene. A solution of hydrogen hexachloroplatinate(IV) in diglyme-isopropyl alcohol (150 ppm Pt) was then added to the reaction mixture. The reaction mixture was stirred at 60 °C for 3 h. At the end of this period, the mixture was refluxed with activated charcoal for 1 h and filtered while hot. Finally the solvent and excess a-olefins were removed under reduced pressure (67 Pa at 100 °C). The reaction proceeded to completion as evidenced by the absence of the Si-H absorption at 2130 cm" in the IR spectra. Residual a-olefin in the purified polymers was determined by gas-liquid chromatography. In all polymers, residual a-olefin was less than 1.5 wt %. 

Block copolymer chemistry provides a convenient means of incorporating the oxygen-RIE-resistant polysiloxane moiety into a high-Tg, radiation-sensitive polymer (20). The flow characteristics of the resist are determined by the unit with higher Tg, and problems associated with phase separation are minimized because of block copolymerization. Specifically, block copolymers of dimethylsiloxane and chlorinated p-methylstyrene exhibit good sensitivity, resolution, and thermal properties and low rates of erosion during O2 RIE. 

The molecular weight poly(dimethylsiloxane) corresponding to each elution volume is determined from the elution calibration curve for this polymer in Fig. 4.30. The corresponding weight fraction Wi is computed from the refractive index difference by the relation... 

Of technical interest is poly(dimethylsiloxane) (PDMS). PDMS is optically clear, and is considered to be inert, non-toxic, and non-flammable. The molar mass determines the viscosity of the polymer. In dependence of M PDMS are viscous oils, pastes, or greases. 

The health and environmental aspects of poly(dimethylsiloxane) fluids have been reviewed. Sea water saturated with poly(dimethylsiloxane) fluid shows no toxic activity against phytoplanktons, molluscs, crustaceans, and fish. The toxicity of the pyrolysis gases from organosiloxane polymer fluids, rubbers, and resins has been shown to be the least toxic from those of 300 materials tested. Two excellent texts have been published on the analysis of silicones both in bulk and additive forms. > A comparative study of techniques for the trace analysis of Si—H and Si—Cl groups in poly(organosiloxane)s shows that levels of 0.01 p.p.m. H and 1.0 p.p.m. Cl bonded to silicon may be determined, ... 

In this case, much larger cyclic ethers are observed up to the E7F and (E2F)3 using a capillary column. The peaks of E2F and F4 overlapped completely when using a non-polar column such as poly(dimethylsiloxane). By using mildly polar poly(methylphenylsiloxane), they were snfficiently resolved. The distributions of E units, as well as the E contents of the polymers, can be determined from the intensities of peaks due to these cyclic ethers obtained if the peaks on the pyrogram reflect the chemical structures in the original polymer chain. 

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