A thorough understanding of gas solubility in confined polymer systems is critical for the development of heterogeneously catalyzed reactions for polymer upcycling as well as advanced gas barrier and separation technologies, yet this area remains relatively underexplored. In this work, we examine the solubility of methanol and n-hexane in polystyrene (PS) and low-density polyethylene (LDPE) confined within mesoporous silica, where the pore dimensions are on the order of the polymers’ radius of gyration (Rg). Thin films of these confined polymers were prepared using capillary rise infiltration (CaRI), and gas solubility was quantified by tracking mass uptakes with a quartz crystal microbalance (QCM). Notably, confinement led to a dramatic enhancement in gas solubility, with increases ranging from tenfold to a hundredfold. Systematic investigations showed that pore size is the primary factor driving this enhancement, while polymer molecular weight and the surface hydrophilicity of the silica matrix have negligible influence. The latter was validated by functionalizing the silica nanoparticles to render them hydrophobic. These results indicate that the observed increase in solubility may be attributed to augmented free volume within the confined polymer matrix. Molecular dynamics simulations support these findings, showing consistently higher hexane uptake in silica-confined polymers compared to bulk systems across both amorphous and crystalline states. Additionally, distinct structural differences observed between virtually and silica-confined crystalline polymers suggest that the confinement environment can further influence polymer morphology and gas uptake behavior. This study highlights how confinment could potentially influence polymer upcycling reactions involving heterogeneous catalysts and also underscores the promise of confined polymer systems for high performance gas barrier and separation membrane applications.
