The gas transport properties of bisphenol A polycarbonate films were examined as a function of the cooling rate during film processing and subsequent physical aging. Interpretation of the permeation properties using results from dynamic mechanical analysis and density measurements indicated that the diffusion coefficient of small gas molecules in glassy polycarbonate is influenced more by the local chain dynamics rather than by the overall free volume content. A one-dimensional lattice model was developed to help probe the effects of the distribution of energy barriers associated with polymer motion on the transport properties. Fast cooling rates generated highly restricted conformations, which hindered local motions leading to increases in the measured activation energy of diffusion. These results correlated well with a lattice model having a broad distribution of energy barriers. Annealing reduced the measured diffusion coefficients, which was shown to be consistent with narrowing of the energy barrier distribution, as well as an increase in the mean barrier energy. Interestingly, the decrease in the diffusion coefficient with aging was found to occur much more slowly in fast-cooled samples, despite the higher initial free volume content. By contrast, properties such as density or isothermal dynamic mechanical properties were more consistent with the free volume model.

Mechanical properties of (woven carbon fiber / vinyl ester matrix) composites can be greatly improved if the interphase between the reinforcing high-strength low-weight fiber and the thermoset resin is made more compliant. In order to improve the adhesion of the vinyl ester matrix to the carbon fiber, a thermoplastic coating such as poly(vinyl pyrrolidone) (PVP) can be used as an intermediate between the matrix and the fiber. The extent of mutual diffusion at the (sizing material / polymer matrix) interphase plays a critical role in determining the mechanical properties of the composite.In this research, the molecular interdiffusion across a poly(vinyl pyrrolidone))/vinyl ester monomer (PVP/VE) interface is being investigated by Fourier Transform Infrared Attenuated Total Reflectance (FTIR-ATR) spectroscopy. The ATR method which can be used to characterize the transport phenomena, offers several advantages, such as the ability to monitor the diffusion in situ or to observe chemical reactions. In order to separate the effects of the vinyl ester monomer diffusion and the crosslinking reaction, ATR experiments were carried out at temperatures below the normal curing temperature. Diffusion coefficients were determined by following variations in infrared bands as a function of time, and fitting this data to a Fickian model. The values of the diffusion coefficients calculated were consistent with values found in the literature for diffusion of small molecules in polymers. The dependence of diffusion coefficients on temperature followed the Arrhenius equation. Hydrogen bonding interactions were also characterized. The diffusion model used in this study, however, does not seem to be appropriate for the particular (PVP/VE) system.Because the glass transition temperature of the PVP changed as diffusion proceeded, one would expect that the mutual diffusion coefficient did not stay constant. In fact, it was shown that the T g can drop by 140 o C during the diffusion process. A more suitable model of the (PVP/VE) system should take into account plasticization, hydrogen bonding, and especially a concentration dependent diffusion coefficient. Further analysis is therefore needed.iv ACKNOWLEDGMENTS