NMR observation of the conformations and motions of polymers confined to the narrow channels of their inclusion compounds

When polymers are guests in crystalline inclusion compounds (ICs) formed wi th small-molecule hosts, they occupy a unique environment. In a cocrystalli zation process the small-molecule host forms a crystalline lattice containi ng long narrow channels where the guest polymer chains are included. Becaus e of the narrow channel diameter and because neighboring channels as separa ted by walls formed exclusively from the small-molecule host lattice, the i ncluded polymer chains are highly extended and separated from polymer chain s in other IC channels. As a consequence, polymer-IC crystals provide a uni que solid state environment for the included polymer chains and serve as mo dels useful for assessing the contributions made by the inherent behavior o f individual polymer chains to the properties of ordered, bulk polymers, wh ich can be obscured by pervasive interactions between their tightly packed polymer chains. In this paper we describe the conformations and motions of polymer chains confined to the narrow channels of the following polymer-ICs : i. polyethylene and trans-1, 4-polybutadiene in their ICs with perhydrotr iphenylene, ii. polyepsilon caprolactone and its diblock and triblock copol ymers with polybutadiene and poly (ethylene oxide) in their ICs with urea, and iii. nylon-6 in its ICs with alpha-, beta-, and gamma-cyclodextrins. Hi gh resolution, solid state NMR serves as both the conformational (C-13 chem ical shifts) and motional (relaxation times and line shapes) probe. Compari son with identical NMR measurements performed on the built homo- and copoly mer samples permits us to draw several conclusions regarding the relationsh ips between the conformations and motions of polymers and their dependence on their ordered solid state environments.