Silicon polymer analysis

ATR-FTIR spectroscopy was used to monitor the uptake of urea into a silicone polymer. Analysis of the time-dependent changes in the IR absorbances of urea and silicone leads to an estimate of the diffusion coefficient for urea that is in close agreement with a value obtained using a bulk transport method (involving radiolabelled permeant). The silicone polymer was medical grade silicone pressure-sensitive adhesive (X7 201). ATR-FTIR is proposed as a rapid and accurate method of rapidly and accurately determining solute diffusion within a polymer matrix. 12 refs. 

Applications of ISS to polymer analysis can provide some extremely useful and unique information that cannot be obtained by other means. This makes it extremely complementary to use ISS with other techniques, such as XPS and static SIMS. Some particularly important applications include the analysis of oxidation or degradation of polymers, adhesive failures, delaminations, silicone contamination, discolorations, and contamination by both organic or inorganic materials within the very outer layers of a sample. XPS and static SIMS are extremely comple-mentar when used in these studies, although these contaminants often are undetected by XPS and too complex because of interferences in SIMS. The concentration, and especially the thickness, of these thin surfiice layers has been found to have profound affects on adhesion. Besides problems in adhesion, ISS has proven very useful in studies related to printing operations, which are extremely sensitive to surface chemistry in the very outer layers. 

The ultimate analysis of organosilicon compounds is an important subject to every worker in the field of siloxane polymers and their intermediates, for without dependable analytical methods the research chemist gropes blindly, at a loss concerning the composition of his products and unable to evaluate the effects of chemical attack. It is the purpose Of this chapter to trace very briefly the development of adequate analytical procedures for organosilicon compounds, with particular emphasis upon those methods which may be used for investigating the composition of silicone polymers. 

This volume has just such a purpose. The first few chapters review the silanes and their derivatives in some detail, in order to provide an understanding of the fundamental chemistry of the nonsilicate compounds of silicon. The later chapters emphasize the silicone polymers which have achieved commercial importance and deal with the methods for their preparation, their chemical and physical properties, and their possible uses. The processes available for large-scale production are treated separately, and a review of methods of analysis is included. In order not to burden the text with definitions and explanations of nomenclature which might already be familiar to some readers, an extensive glossary of terms is appended. 

The stmctural architecture of silicone polymers, such as the number of D, T, and Q sites and the number and type of cross-link sites, can be determined by a degradative analysis technique in which the polymer is allowed to react with a laige excess of a capping agent, such as hexamethyldisiloxane, in the presence of a suitable equilibration catalyst (eq. 38). Triflic acid is often used as a catalyst because it promotes the depolymerization process at ambient temperature (444). A related process employs the KOH- or KOC2H -catalyzed reaction of silicones with excess Si(OC2H5)4 (eq. 39) to produce ethoxjiated methjisilicon species, which are quantitatively determined by gc (445). 

Various attempts have been made in the past to determine the contents of various functionalities in silicone polymers by cleavage of the siloxane linkage and analysis of the monomers formed thereby [1], Considerable experimental problems, especially the difficulty of reliably preventing the cleavage of Si-C bonds and of achieving the sensitivity necessary for trace analysis, have resulted in these methods not being used in routine analysis [2]. 

An important example of a non-ISRP phase is the shielded hydrophobic mixed funchon material known as Capcell Pak MF . This phase consists of porous silica derivahzed with a silicone polymer. The polymer is referred to as a mixed phase, since it contains hydrophobic moiehes dispersed at intervals in the polymer chain. Unlike small molecules, matrix proteins are unable to penetrate the hydrophilic polymer and are eluted to waste. A recent appUcahon by Hsieh et al. demonstrated the utility of this phase for direct plasma analysis without the use of a secondary column [70]. 

Presentation and discussion of the experimental results will proceed in the following manner. First the absorption spectra of the polysilylenes will be described and a conq)arative analysis of the spectra in room temperature fluid solvent media and rigid low temperature glasses at 77°K made. This will be followed by a description of the rather remarkable emission properties of these materials with emphasis on results obtained at 77°K. Included as part of the emission spectroscopic properties are the results of photoselection or polarization of emission measurements obtained in a rigid glass at 77°K. Based on these results a model is developed which describes individual chains of these silicon polymers in terms of a distribution of all-trans sequences with variable effective conjugation lengths. 

The increasing demand for thermally stable polymers as electronic encapsulants is consistently creating a need for more information on such materials. Thermogravimetric analysis (TGA) is a valuable tool for the thermal analysis of the silicone polymers. 

Ohnishi, M. Suzuki, K. Saigo, Y. Saotome, and H. Gokan, Postirradiation polymerization of e beam negative resists Theoretical analysis and method of inhibition, Proc. SPIE 539, 62 (1985). " R.R. Kunz, M.W. Horn, R.B. Goodman, P.A. Bianconi, D.A. Smith, J.R. Eshelman, G.M. Wallraff, R.D. Miller, and E.J. Ginsberg, Surface imaged silicon polymers for 193 nm excimer laser lithogra phy, Proc. SPIE 1672, 385 (1992). 

TABLE II. Infrared Spectrophotometric Analysis of The Condensable Volatiles From Silicone Polymers ... 

Gas-Liquid Chromatographic Analysis Fluphenazine was not eluted after 90 minutes at 270°, using a 210 SE-30 silicone polymer on a 80-100 mesh Gas-chrom S diatomaceous earth column with a 3% SE-30 on 80-100 mesh Gas-chrom Q at 250°C, it eluted in 4.9 minutes. Fluphenazine was also well separated from other tranquilizers on a 120 mesh silanized Gas-chrom P column coated with 1% Hi-Eff-8B (cyclohexane-dimethanol succinate) at a temperature of 220°C and a retention time of 5 minutes. The identification of fluphenazine and other phenothiazine tranquilizers by gas chromatography of their pyrolysis products has also been reported. 

Another major source of contamination in an analysis can be the analyst. It depends on what kinds of analytes are being measured, but when trace or ultratrace levels of elements or molecules are being determined, the analyst can be a part of the analytical problem. Many personal care items, such as hand creams, shampoos, powders, and cosmetics, contain significant amounts of chemicals that may be analytes. The problem can be severe for volatile organic compounds in aftershave, perfume, and many other scented products and for silicone polymers, used in many health and beauty products. Powdered gloves may contain a variety of trace elements and should not be used by analysts performing trace element determinations. Hair, skin, and clothing can shed cells or fibers that can contaminate a sample. 

Karayannis and Corwin have applied hyperpressure gas chromatography to the analysis of various etioporphyrin II metal chelates including that of zinc. Gas chromatography is carried out at 145 0 and 1000 - 1700psi pressure using dichlorodifluoroethylene as carrier gas and 10% Epon 1001 on Chromosorb or 10% XE 60 (cyano-ethylmethyl silicone polymer) on Chromosorb as stationary phase. 

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