SORPTION AND DIFFUSION OF N-ALKANES INTO BROMOBUTYL RUBBER MEMBRANES

Sorption and diffusion of n-alkanes into bromobutyl rubber membranes w ere investigated in the temperature interval 25-60 degrees C by a sorp tion gravimetric method. The Fickian diffusion equation was used to ca lculate the diffusion coefficients, which were dependent on the size o f the alkanes, their interactions with the chain segments of the polym er and temperature. The diffusion coefficients varied from 0.34 x 10(- 7) cm(2)/s (n-hexadecane) to 9.94 x 10(-7) cm(2)/s (n-hexane). The act ivation energy for diffusion varied from 14 kJ/mol (n-hexane) to 27 kJ /mol (n-hexadecane). Heat of sorption ranged from -1.4 kJ/mol for n-he ptane to 2.0 kJ/mol for n-hexadecane. The sorption/swelling results ar e discussed in terms of first and second order kinetic equations. The molar mass between chain-entanglement-crosslinks was estimated from sw elling data. The experimental and calculated results showed a systemat ic dependence on the increasing size of the alkanes. None of the solve nts showed any degradative effects on the polymer.