New strategies in chemical recycling of plastics require the use of catalysts onto which long-chain polymers adsorb and subsequently undergo reaction. We examine interactions of well-defined models for polyethylene (n-hexatriacontane, C36H74, and two low density polyethylene (PE) materials with narrow molecular weight distributions) under catalytically relevant melt-phase conditions with mesoporous silicas of varied pore size that are commonly used as supports for catalytic active sites. Thermogravimetric analysis (TGA) combined with post-reaction toluene extraction and differential thermogravimetric (DTG) analysis distinguished weakly and strongly adsorbed alkane chains, with a persistent fraction indicating strong polymer–surface association not attributable to coke formation. The amount of strongly, and essentially irreversibly, adsorbed model PE on each mesoporous silica depended on the ratio of the radius of gyration (Rg) for the polymer and the pore radius (Rg/Rpore), indicating that the strong adsorption occurred within mesopores. Together, these results demonstrate that the balance between pore size and polymer size governs both the extent and energetics of polymer-support interactions, providing design guidelines for tailoring mesoporous silicas to enhance catalyst selectivity and stability in polyethylene recycling.
