The diffusion of methyl ethyl ketone (MEK) in two vinyl alcohol/vinyl butyr
al (VA/VBu) copolymers (11- and 19-wt. % VA) was studied at low vapor activ
ities using Fourier transform infrared-attenuated total reflectance (FTIR-A
TR) spectroscopy. MEK has the ability to interact through hydrogen bonding
to sites in the polymer- and was chosen to study the effect of penetrant-po
lymer solvation on molecular diffusion. The assumption of local equilibrium
was verified by examining the time-evolved concentrations of hydogen-bound
and free MEK determined from the carbonyl (C = O) stretching bands. A math
ematical model that accounted explicitly for solvation during the diffusion
process was developed Solvation hinder ed the diffusion of MEK in the VA/V
Bu copolymer by factors of 2.0 (11-wt. % VA) and 2.6 (19-wt % VA). After se
parating solvation front diffusion true diffusion coefficients of MEK were
compared to those of methylene chloride (CH2Cl2), a noninteracting penetran
t of similar size to MEK. Within experimental error, true diffusion coeffic
ients for MEK were the same as those for CH2Cl2 over the concentration rang
e studied.