Detection of free radicals by radical trapping and 15N NMR spectroscopy in copolymerization of methyl acrylate and styrene

The macroradicals taking part in the copolymn. of Me acrylate and styrene were trapped by reaction with a 15N labeled stable nitroxyl radical at 70 DegC. The nitroxyl radical is formed in situ from a thermally instable alkoxyamine precursor. 15N NMR spectroscopy is applied to detect the trapping products. It enables to identify the terminal units of the trapped macroradicals from the chem. shift of their spectral bands in the 15N NMR spectrum. Integration of the spectra also enables to est. the concn. ratio A of the macroradicals having Me acrylyl and styryl terminal units. This parameter depends on the fraction of Me acrylate in the monomer feed f(MA) as follows: A <0.45 at f(MA) = 0.97; A <0.3 at f(MA) = 0.96; A <0.13 at f(MA) = 0.93.