Polymer Inclusion Compounds: Model Systems for Ordered Bulk Polymer Phases and Starting Materials for Fabricating Polymer-Polymer Molecular Composites

Abstract

Several small molecules can be cocrystallized with polymers to form inclusion compounds (ICs). Urea, perhydrotriphenylene and the cyclodextrins are examples, and serve to form the host crystalline lattice containing the guest polymer chains in their ICs. The guest polymer chains are confined to narrow, cylindrical channels created by the host, small-molecule lattice, where the polymers are highly extended as a consequence of being squeezed, and are separated from neighbouring polymer chains by the IC channel walls composed exclusively of the small-molecule lattice. The net result is a unique solid-state environment for polymers residing in IC channels, which can be utilized as model systems for ordered, bulk polymer phases. Comparison of the behaviour of polymer chains isolated and extended in IC crystals with the behaviour observed for ordered, bulk phases of polymers is beginning to permit an assessment of contributions made by the inherent, single chain and the cooperative, interchain interactions to the properties of ordered, bulk polymers. It is also possible to release and coalesce polymers from their IC crystals in a manner which leads to their consolidation with a chain-extended morphology. Embedding polymer IC crystals into a carrier polymer, followed by in situ release and coalescence of the included polymers from their IC crystals, offers a means to obtain polymer-polymer composites with unique morphologies. Several such polymer IC-generated composites are described and it is suggested that their unique morphologies might translate into useful, tailorable properties, as well as providing a means for addressing several questions that are fundamental to the behaviour of both phase-separated and homogeneous polymer solids.