Quantifying macroradical yields in peroxide-initiated polyolefin modifications

Abstract

A sensitive and versatile technique for measuring H-atom abstraction yields of peroxides acting on polyolefins is developed and applied for the analysis of reactive polymer blending. 4-(1-Naphthoyloxy)-2,2,6,6-tetramethylpiperidine-1-oxyl (NTEMPO) is used to trap alkyl macroradicals as their corresponding alkoxyamines to introduce a polymer-bound fluorophore at the site of H-atom abstraction. Quantifying alkoxyamine yields by fluorescence spectroscopy determines the initiator’s abstraction efficiency, defined as the fraction of alkoxy radicals that engage in H-atom transfer with a polymer versus cleaving to ketone + methyl radical. Comparisons between fluorescence and gas chromatography analyses of model hydrocarbon products confirm the accuracy of the method before extending to reactive blending processes that undergo simultaneous peroxide thermolysis and interphase mass transfer. These results are discussed in terms of a dynamic model of the instantaneous concentrations of initiator in each phase of a reactive blending system that accounts for both thermodynamic partitioning and kinetic rate effects.