MOLECULAR MODELING OF POLYMERS .16. GASEOUS-DIFFUSION IN POLYMERS - AQUANTITATIVE STRUCTURE-PROPERTY RELATIONSHIP (QSPR) ANALYSIS

Purpose. The purpose of this study was to identify the key physicochem ical molecular properties of polymeric materials responsible for gaseo us diffusion in the polymers. Methods. Quantitative structure-property relationships, QSPRs were constructed using a genetic algorithm on a training set of 16 polymers for which CO2, N-2, O-2 diffusion constant s were measured. Nine physicochemical properties of each of the polyme rs were used in the trial basis set for QSPR model construction. The l inear cross-correlation matrices were constructed and investigated for colinearity among the members of the training sets. Common water diff usion measures for a limited training set of six polymers was used to construct a ''semi-QSPR'' model. Results. The bulk modulus of the poly mer was overwhelmingly found to be the dominant physicochemical polyme r property that governs CO2, N-2 and O-2 diffusion. Some secondary phy sicochemical properties controlling diffusion,including conformational entropy, were also identified as correlation descriptors. Very signif icant QSPR diffusion models were constructed for all three gases. Cohe sive energy was identified as the main correlation physicochemical pro perty with aqueous diffusion measures. Conclusions. The dominant role of polymer bulk modulus on gaseous diffusion makes it difficult to dev elop criteria for selective transport of gases through polymers. Moreo ver,high bulk moduli are predicted to be necessary for effective gas b arrier materials. This property requirement may limit the processing a nd packaging features of the material. Aqueous diffusion in polymers m ay occur by a different mechanism than gaseous diffusion since bulk mo dulus does not correlate with aqueous diffusion, but rather cohesive e nergy of the polymer.