Analysis of polysiloxanes by alkali fusion reaction gas chromatography

Abstract

The technique of alkali fusion reaction gas chromatography has been applied to the determination of alkyl and aryl groups in polysiloxanes. The method involves the quantitative cleavage of ail organic substituents bonded to silicon, producing the corresponding hydrocarbons. Reactions are driven to completion, with no apparent decomposition, in less than 10 minutes by fusing the sample with potassium hydroxide in an Inert atmosphere. After concentration of the volatile products, they are separated and determined by gas chromatography. Sample losses are minimized by performing the total analysis in a single piece of apparatus. Fluids, gum rubbers, and resins are handled with equal ease. The percent relative standard deviation of the method is 1.0%; the average deviation between experimental and theoretical or check method results Is 0.5% absolute.Polysiloxanes, also referred t o as silicones or polyorganosiloxanes, are commercially important because of unique properties resulting from their dual organic-inorganic composition. The analytical chemistry of this class of polymers has been reviewed in a recent monograph by Smith ( I ) .Spectrometric techniques, such as IR and NMR, are powerful tools for the qualitative and quantitative analysis of many functional groups in t h e intact polymer. Alternatively, these organic substituents can be cleaved from the polymer to produce simple compounds that can b e determined by chemical or instrumental techniques.Alkyl and aryl substituents are readily detected by t h e above approaches, b u t quantitative analyses of these groups may be difficult with existing methodology. Instrumental techniques such as N M R (2, 3 ) , IR (4-13), and UV (14-17) spectrometry are useful for analyzing methyl and/or phenyl groups in silicone polymers, but they are generally unable t o differentiate isomers or homologues. Chemical cleavage coupled with a separation technique is a more selective approach. Several reaction-based methods have been reported for t h e quantitative determination of alkyl and aryl groups

Chromatographic analysis of some condensation polymers after alkali fusion

“…Thus, within the group may be included the poly(amide hydrazides) and related copolymers developed by Monsanto and the poly(quinazo1inediones) developed and formerly marketed by Bayer. The first polymers of the class examined were poly(mphenyleneisophthalamide) (I), currently marketed as Nomex and developed several decades ago, followed by t (11) The three phenylenediamine isomers were readily separated on a nonpolar OV-1 column, the peaks being essentially ~y m m e t r i c a l .~~ The three isomeric methyl phthalates are readily separated by gas chromatography using a polar cyanoalkylsiloxane stationary phase. 25 The phenylenediamines are also separated by HPLC, but separation of the three phthalate esters has not yet been reported, although separation using an amine column would be expected to be successful.…”

“…Analyses of -aminoalkanoic acids as the methyl esters were carried out on nylon 6 ( -aminocaproic acid), nylon 11 ( -amino-n-undecanoic acid), and nylon 12 ( -amino--dodecanoic acid), the percentage error being 1.8, 2.2, and 2.0, respectively. The particular value of the procedure was immediately evident, as a complete analysis was possible in a fraction of the time necessary for the procedure of Anton,16 while with the method of Siggia7 all of the polymers and copolymers shown in Tables II and III would give the same product, i.e., 1,6-diaminohexane.…”

Characterization of silicone phases by alkaline hydrolysis and CGC analysis

“…For this, the different monomer units must be known. Decomposition of stationary phases can be realized by alkali fusion [2], by pyrolysis and hydrolysis. Alkali fusion can be applied to the determination of alkyl and aryl groups in silicones.…”

Decomposition Procedure Using Methyl Orthoformate to Analyze Silicone Polymers

“…Chemical decomposition methods to analyze silicone reported to date include ethoxysilane degradation, 5,6 fluorosilane degradation, 7 alkali fusion method, 8,9 etc. The ethoxysilane degradation method decomposes the siloxane bond by heating through the reaction under alkaline conditions with the addition of tetraethoxysilane to the silicone samples.…”