IN-SITU DETECTION OF HINDERED AMINE STABILIZER CONSUMPTION IN POLYMERTHROUGH OXIDATION BY INDIRECT ELECTRON-SPIN-RESONANCE

The stabilization mechanisms of hindered amine stabilizers (HAS) invol ve various oxidation products oft;he piperidine structure. Thus, we pr opose a novel method, based on electron spin resonance (ESR) spectrosc opy, to check in situ the consumption of the total piperidyl species ( intact HAS and all of its byproducts) in polypropylene (PP) films thro ugh photooxidation. First, the concentration of nitroxyl radicals prod uced upon irradiation in stabilized PP has been measured by direct ESR analysis. Then, the changes of concentration of the overall stabilizi ng species have been detected by indirect ESR, after conversion of the overall HAS derivatives into nitroxyl-free radicals by exposure of ph otooxidized PP to peracetic acid vapor at room temperature. Results we re compared with those obtained by the conventional Fourier transform infrared method in the particular case of [2,2,6,6-tetramethyl piperid inyl] sebacate, and the reliability of both techniques was discussed. Thus, we assume that indirect ESR experiments consist of a easy, accur ate, and very sensitive method to monitor the time evolution of a low- molecular weight HAS-NH concentration in PP upon photooxidation. (C) 1 998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1107-1114, 1998.