Non-Fickian diffusion of a flame-retardant plasticizer, resorcinol bis
(diphenyl phosphate) (RDP), in a glassy poly(ether imide), Ultem(TM),
was measured with Rutherford backscattering spectroscopy (RES). Volume
fraction versus depth profiles were obtained as a function of time, t
emperature and externally applied stress in experiments where a limite
d supply of RDP was initially present on the surface of the Ultem. The
profiles of the plasticizer in the glassy polymer in all samples had
sharp diffusion fronts with constant volume fraction behind the front.
The limited-supply boundary condition requires that the volume fracti
on, phi, of RDP in the plastized zone decreases as penetration depth i
ncreases. Isochronal values of phi decrease with increasing temperatur
e. At long times, phi approaches a Value such that the material in the
plasticized zone has a glass transition temperature equal to the temp
erature of the experiment. At 140, 160 and 180 degrees C, phi decrease
d in direct proportion to the logarithm of time. At 120 degrees C, two
regimes of diffusion behaviour were observed in a plot of phi versus
log time. Short-time, high-phi behaviour corresponds to case II diffus
ion, and long-time, low-phi behaviour corresponds to anomalous diffusi
on. Only the regime of anomalous diffusion was observed at the higher
temperatures. Externally applied biaxial tensile or compressive stress
es of order 10 to 40 MPa in the plane of the sample had no effect on d
iffusion normal to the plane in experiments at 120 degrees C lasting 1
or 72 h.