Effect of penetrant-polymer interactions on molecular diffusion in conformational isomers of a heterogeneous polymer

The diffusion of deuterated hexane in conformational isomers of a heterogen eous polymer, H12MDI (4,4'-dicyclohexylmethane diisocyanate)BD (1,4-butaned iol)/PTMO (poly(tetramethylene oxide)), was investigated at a fixed hard se gment content of 30 wt % and compared to the diffusion of acetonitrile. The effective diffusion coefficient of acetonitrile decreases with increasing trans-trans isomer content while that for deuterated hexane remains constan t. These results suggest that the trend observed from acetonitrile diffusio n is a function of penetrant-polymer interactions and not tortuosity effect s. A model with penetrant-polymer binding to the surface of the dispersed h ard segment domains of the heterogeneous polymer was developed to elucidate the main factors contributing to the interaction or hindrance effect, whic h were determined to be the "available" surface binding sites and the surfa ce-to-volume ratio of the hard segment domains. FTIR-ATR spectroscopy was u sed to quantify this interaction effect, and SAXS was used to confirm the f indings.