Probing polymer colloids by 129Xe NMR

Model aqueous dispersions of polystyrene, poly(methyl methacrylate), poly(n-butyl acrylate) and a statistical copolymer poly(n-butyl acrylate-co-methyl methacrylate) were studied using xenon NMR spectroscopy. The (129)Xe NMR spectra of these various latexes reveal qualitative and quantitative differences in the number of peaks and in their line widths and chemical shifts. Above the glass transition temperature, exchange between xenon sorbed in the particle core and free xenon outside the particles is fast on the (129)Xe spectral time-scale and a single (129)Xe signal is observed. At temperatures below the glass transition temperature, the exchange between sorbed and free xenon is slow on the (129)Xe spectral time-scale and two (129)Xe NMR signals can be observed. If the signal of sorbed (129)Xe is observed, its chemical shift, line width and integral relative to the integral of free (129)Xe can be used for the characterization of the particle core. The line width of free (129)Xe provides the residence time of xenon outside the particles and can be used to determine the rate constant characterizing the kinetics of penetration of xenon in the particles. This rate constant emerges as promising parameter for the characterization of the polymer particle surface.
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