Separation of polymers and small molecules by crystalline host systems

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