The BHT release in isooctane from the PU film should be almost complete because it is not limited by solubility. Although solubility data for BHT in isooctane is not available, this additive has good solubility in organic solvents (Schwope et al., 1987), much higher than the total amount of BHT incorporated into the film. However,
as observed in previous works (Anbinder, 2011), BHT interaction
with the polymer form hydrogen bonds between the phenolic
OH groups of BHT molecules and the nitrogen of the urethane
groups, AN(H)AC(O)OA, of polyurethane (see Supplementary
material), affecting the total release of the additive (Bart, 2005).