EFFECT OF DEGREE OF SWELLING ON ACTIVATION VOLUME FOR THE DIFFUSION OF p-NITROANILINE IN POLY (ETHYLENE TEREPHTHALATE)

Abstract

Activation volume (ΔV^_??_) for the diffusion of p-nitroaniline (pNA) in poly (ethylene terephthalate) (PET) was studied at 100°C from the pressure dependence of the diffusion coefficient (D). The diffusion was carried out under pressures up to 1000bar and in n-butanol (BuOH)/water mixed solvent in which pNA was dissolved. The BuOH concentration in the mixed solvent could be varied in limited ranges because of the immiscibility of the two solvents, from 0 to 6.9% (1st range) and 80 to 100% (2nd range), which could result in a linear increase of the degree of swelling of the polymer in the 1st range, while it almost levelled off in the 2nd range.
It was found that ΔV^_??_ decreased in a sensitive manner with increase of the BuOH content in the 1st range, giving 92.8 and 26.6 cm³/mol at the BuOH concentration of 0 (pure water) and 6.9%, respectively. In the 2nd range, however, ΔV^_??_ was approximately constant, 50cm³/mol. On the other hand, a significant increase of D with increase of BuOH content was obtained in the lst range. Under the atmospheric pressure, for example, D at the BuOH concentration of 6.9% was about 16 times larger than that obtained in pure water.
The above relation among ΔV^_??_, D and the BuOH concentration was qualitatively explainable from the degree of swelling of the polymer, in relation with the free volume and the occupied volume of pNA molecule (99cm³/mol). A quantitative explanation attempted by using Fujita's theory was not much successful, giving unexplainably large values of f(0, T), β (T) and γ (T).