DETERMINATION OF THE GLASS-TRANSITION TEMPERATURE OF POLY(CYCLOHEXYL ACRYLATE) FROM OXYGEN PERMEABILITY MEASUREMENTS

The glass transition temperature (T(g)) of poly(cyclohexyl acrylate) (PCA) has been obtained from measurements of the oxygen permeability (P=0.60 barrers, T(g)=23.5+/-2.0-degrees-C) using a potentiostatic electrochemical sensor, and from the oxygen diffusion coefficient (D=0.12 x 10(-8) cm2 s-1, T(g)=24.0+/-1.8-degrees-C) by the time-lag method. A T(g) of 25+/-1-degrees-C was found by differential scanning calorimetry and a T(g) of 25.0+/-3.5-degrees-C was obtained from the specific volume by dilatometry. The fractional free volume (v(f)) at T(g) is 0.020+/-0.002, which is slightly below (approximately 20%) most glassy polymers. A linear correlation has been observed between In D and the reciprocal of v(f), which suggests that the polymer morphology is not influenced by the presence of oxygen. The diffusion coefficient of oxygen through PCA membranes follows Arrhenius behaviour and has an activation energy of 26+/-2 kcal mol-1, a surprisingly high value considering that the range of activation energies observed in most systems is 1-20 kcal mol-1.