TRANSPORT OF DICHLOROMETHANE IN POLY(ETHER IMIDE) FILMS - EFFECT OF THE SOLVENT ACTIVITY AND TEMPERATURE

The sorption and diffusion of dichloromethane liquid in a wide range o f activities and at different temperatures in poly(ether imide) (PEI) films was studied. They were prepared by solution casting at slow solv ent evaporation conditions. The sorption behavior is characterized by two zones depending on temperature and penetrant activity. In zone I, at low activity, the isotherms follow Henry's law. The range of activi ty between 0.25 and 0.30 is characterized by a negative deviation from Henry's law and shows an accentuated dependence on previous thermal h istory of the films. In zone II, with a range of activity higher than 0.35, the isotherms follow Flory-Huggin's behavior. In both zones, the diffusional behavior, based on sorption measurements, shows a linear relationship between the diffusion coefficient and the equilibrium sor ption concentration of dichloromethane. In the activity range between 0.25 and 0.35, an accentuated discontinuity indicates a possible confo rmational structural change in the original polymeric matrix of the PE I films induced by the plasticization effect of the dichloromethane. C orrelations between transport properties and infrared analysis confirm this proposition. The study of diffusion at different temperatures ma kes possible the Arrhenius plot analysis of the thermodynamic diffusio n coefficient. Two different linear relationships were obtained for zo nes I and II with activation energies E-a = 30803 J . mol(-1) and E-a = 13613 J . mol(-1), respectively. These results indicate that the con formational change (zone I and zone II) observed is typically exotherm ic and therefore permits the proposition that the structural PEI forme d in zone II is more ordered than in the zone I, corroborating the neg ative deviation of Henry's law. The two Arrhenius plots intersect at 1 50 degrees C. PEI films annealed at this temperature show a dichlorome thane sorption without negative deviation. On the other hand, PEI exhi bits a T-beta transformation at 70 degrees C related to the conformati onal changes of the benzimide groups. The results obtained for the PEI films annealed at 150 degrees C confirm that the conformational chang e observed is related to the benzimide groups. This fact was also conf irmed by infrared analysis. Finally, the study of diffusion at differe nt temperatures allowed creation of a temperature-penetrant concentrat ion diagram, which is very useful for visualizing the different behavi or zones.