A new experimental approach for measuring diffusion coefficients of so
rbed gas in polymers has been developed based on a combination of NMR
spectroscopy and the use of polymer microspheres. The system chosen to
demonstrate the technique is xenon gas sorbed into polystyrene beads
of micron size. Pressures in the range of 10-15 atm are sealed in NMR
tubes containing a gram or so of polymer. Chemical shift exchange of t
he xenon gas is easily monitored in either one or two dimensions throu
gh the xenon-129 resonances since well-separated signals are observed
for the sorbed and free gas. To quantitatively determine diffusion coe
fficients, selective saturation of the gas phase resonance is used to
reduced that signal to zero. Then the decay of the sorbed signal is mo
nitored as a function of saturation time to determine the rate of diff
usion of gas out of the polymer microsphere. Diffusion in this case is
simply described mathematically by diffusion out of a sphere. A model
has been developed to take into account the effects of diffusion in c
ombination with spin-lattice relaxation of the xenon-129 sorbed in the
polymer. The diffusion coefficient of xenon in polystyrene at 25 degr
ees C is (1.9 +/- 0.4) x 10(-9) cm(2)/s. Measurements were made up to
115 degrees C and an apparent activation energy of 36 kJ/mol was found
for diffusion in glassy polystyrene with a sharp increase in the diff
usion coefficient when the glass transition region was reached.