Tris(o-phenylenedioxy)cyclotriphosphazene can entrap and separate various polymers and small molecules within its tunnels based on their microstructure, molecular weight, and end group functionality. Inclusion adducts with polyethylene, poly(tetramethylene oxide), poly(ethylene glycol), and 1,4-polybutadiene show a preferential inclusion for the type of polymer that will best stabilize the hexagonal structure of the host. Separations based on end groups show preferential inclusion of the species with the more hydrophobic end groups, possibly a response to the hydrophobic tunnels of the host. Exposure of the host to various small-molecule n-alkanes with different chain lengths revealed a preferential clathration of the longer chain species. Similarly, high polymers are preferentially included within the tunnels:compared to analogues with lower molecular weights, presumably due to enhanced van der Waals interactions with the host. The polydispersity index was also improved by clathration, suggesting that the host can be used as a means to fractionate polymers on the basis of chain length.