| Abstract
| - The dispersion of brominated flame retardants in polymers ismonitored with 81Br nuclearquadrupole resonance (NQR) using a pulse NQR spectrometer. The NQRspectrometerconsists of a homemade 10−300 MHz single-channel NMR console coupledto a broadlytunable probe. The probe is a loop−gap resonator usable from 220to 300 MHz and isautomatically tuned over any 5 MHz region with a stepping motor and aradio frequencybidirectional coupler. 81Br NQR spectra ofseveral brominated aromatic flame retardants,as pure materials and in polymers, were recorded in the range of 227 to256 MHz in zeroapplied magnetic field. Two factors affect the79/81Br NQR transition frequencies inbrominated aromatics: electron-withdrawing substituents on the ringand intermolecularcontacts with other bromine atoms in the crystal structure. Anexisting model forsubstituents is updated, and a point charge model for theintermolecular contacts isdeveloped. In this study, we exploit the 81Br NQRtransition frequency dependence onintermolecular contacts to learn how a flame retardant is dispersed ina polymer matrix.Additionally, the crystal structure for1-bromo-4-(4-bromophenoxy)benzene and the 100 Kstructure of 1,2,4,5-tetrabromobenzene were determined.
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