Modeling the conformations and motions of isolated polymer chains in the narrow channels of their crystalline inclusion compounds with small‐molecule, host clathrates

Abstract

AbstractThe narrow channels occupied by polymer chains in their crystalline inclusion compounds(IC) with small‐molecule, host clathrates, such as urea and perhydrotriphenylene(PHTP), provide a unique, solid state environment. Single polymer chains are confined to occupy narrow cylindrical channels whose walls consist of a crystalline matrix of the small‐molecule, host clathrate. Because the IC channels are well‐separated, each included polymer chain is isolated from its neighbors, and is therefore free from cooperative, interpolymer interactions which often dominate and complicate the behavior of bulk polymers. We have modeled polymer chains included in their IC channels by restricting the conformations accessible to small chain fragments(9–20 backbone bonds) to those which fit into a cylinder whose diameter(5.5Å) mimics the observed channel cross‐section. After establishing the population of channel conformers, a test is performed to determine the possibility of interconverting between them without any portion of the polymer chain fragment leaving the channel during any step in the interconversion process. The results of our modeling are compared to observations made on a variety of polymer‐IC's formed with either or both of the host clathrates, urea and PHTP. General agreement is found between the modeled conformations and mobilities of cylindrical polymer chain fragments and those observed directly from the crystalline polymer‐IC's, principally by solid state NMR, DSC, and X‐ray diffraction.