NMR observations of isolated and stretched polymer chains in their crystalline inclusion compounds formed with small‐molecule host clathrates

Abstract

AbstractSeveral small‐molecule hosts form clathrates or inclusion compounds (ICs) with polymers. In these polymer‐ICs the guest polymer chains are confined to occupy narrow channels in the crystalline matrix formed by the host. The walls of the IC channels are formed entirely from the molecules of the host, and they serve to create a unique solid‐state environment for the included polymer chains. Each polymer chain included in the narrow, cylindrical IC channels (ca 5.5 Å in diameter) is highly extended and also separated by the host matrix channel walls from neighboring polymer chains. The net result is a solid‐state environment where extended, stretched (as a consequence of being squeezed) polymer chains reside in isolation from their neighbors inside the narrow channels of the crystalline matrix provided by the small‐molecule host. Comparison of the behavior of isolated, stretched polymer chains in their crystalline ICs with observations made on ordered, bulk samples of the same polymer are beginning to provide some measure of the contributions made by the intrinsic nature of a confined polymer chain and the pervasive, cooperative, interchain interactions which can complicate the behavior of bulk polymer samples. Just as dilute polymer solutions at the θ temperature have been effectively used to model disordered, bulk polymer phases (both glasses and melts), polymer‐ICs may be utilized to increase our understanding of the behavior of polymer chains in their ordered, bulk phases as found in crystalline and liquid‐crystalline samples. Solid‐state NMR observations of polymer‐ICs can provide detailed conformational and motional information concerning the included, stretched and isolated polymer chains.