Chemical separations account for ten percent of the world energy consumption. Although membrane-based separations would improve the energy efficiency of existing processes by ninety percent, currently they cover only twenty percent of the total separation market. The permeability/selectivity trade-off and polymers long-term instability are critical issues that hamper the membrane market expansion. Unfortunately, synthetic approaches capable of addressing these issues simultaneously are not yet available. To suppress physical aging and plasticization, while simultaneously enhancing permeability and selectivity in gas and vapor separation, we blend commercial and in-house synthesized microporous polymers with hyper-crosslinked Porous Polymer Networks (PPNs), whose monomers and structures are designed using molecular simulation and DFT calculations. Supported by a body of preliminary data, we hypothesize that polymer chains can thread and interlock through the network porosity. This phenomenon, in synergy with polymer-PPNs-penetrant interactions and the configurational free volume exhibited by PPNs, is expected to regulate penetrant transport rate, selectivity and membrane long-term stability. Polymers, PPNs and their interfaces are studied at the molecular level to identify structural and functional features (e.g., stiffness, pore size, chemical interactions) that control selective penetrant transport and polymer threading through the PPN pores under various conditions. To accomplish this, molecular modeling and synthetic chemistry are used in parallel to understand the mechanisms of mass transport. This hypothesis-driven project will contribute to the development of devices for energy-efficient and durable separations, as well as to the development of a diverse workforce.