This project aims to elucidate the transport mechanisms underlying “preferential pathways” in porous polymer network membranes with the goal of enhancing selectivity and dynamic range of gas phase molecules during chemical separations. Preferential pathways is a mechanism in which gas mixtures undergo separation by one gas preferentially sorbing to and the second preferentially diffusing through dense porous polymer networks. Enthalpic factors are hypothesized to determine the diffusion pathway for a given penetrate, thus reducing the entropic penalty is expected to be related to penetrant size. Thus, the trade-off between sorption- and diffusion-selectivity are expected to be mitigated. Three tasks are proposed including (1) elucidating the molecular mechanism underpinning preferential pathways, (2) identifying the membrane and permeating mixture properties that control and activate preferential pathways, and (3) experimentally validating and connecting preferential pathways and membrane dynamic range. Both experimental and computational approaches, including molecular dynamics (MD) simulations, in situ Fourier Transform infrared spectroscopy (FTIR) and sorption/permeation measurements with dilute multicomponent mixtures, are used to understand and quantify the molecular interactions responsible for preferential pathways, while also identifying interaction sites and binding energy ranges that activate this transport mechanism. The project aligns with the mission of the BES Separation Science program as it seeks to understand and predict mechanistic paradigms for removal of dilute constituents from a mixture via their emergent phenomena from unique transport properties for gas phase molecules using blended polymer membranes.