Studies of the crosslinking degree of linear polyurethanes. Part II. Determination of the content
of secondary nitrogen atoms in a model compound and in urethane elastomers
A method for the determination of the content of secondary nitrogen atoms in a model compound — n-butyl carbanilate — and in samples of urethane elastomers has been presented. This method consists in the utilization of the selective reaction of imine groups contained in the urethane and urea groups of polyurethane with trifluoroacetic anhydride and of the reaction of the thus-formed derivative with aniline. In the last-mentioned reaction N-phenyltrifluoroacetamide is formed and it is determined quantitatively by a gas-chromatographic method in respect to an internal standard — n-tridecane. The crosslinking degree of urethane elastomer is calculated on the basis of its content of secondary nitrogen atoms and total content of nitrogen by Kjeldahl method. Results of determinations in this way of crosslinking degree for several samples of urethane elastomers have been presented.
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