α- and γ-cyclodextrin in columnar structures with only water molecules included were successfully obtained by appropriate recrystallization from their aqueous solutions. These crystals were found to adopt a channel-type structure similar to the cyclodextrin inclusion compounds formed with guest polymers. Experimental investigations of their inclusion properties demonstrate that only α-cyclodextrin in the columnar structure (α-CDcs) is able to include both small molecules and polymers. Thermal measurements reveal that columnar structure α-CDcs contains three different types of water molecules. The most strongly held water molecules are located outside of the cyclodextrin cavity, likely hydrogen-bonded between the rims of neighboring cyclodextrins in the columnar α-CD stacks. X-ray analyses confirm that the channel structure is preserved in the dehydrated α-CDcs and its inclusion compounds formed with various guests. In contrast, a completely different behavior was observed for γ-CDcs in the columnar structure. It appears that α-CDcs, at least, can function as a nanoscopic filter for separating both small molecules and polymers on the basis of their abilities to be included, or not, in the narrow (∼0.5 nm) channels of the α-CDcs crystals.

Bulk poly(ethylene terephthalate) (PET) and bisphenol A polycarbonate (PC) samples have been produced by the coalescence of their segregated, extended chains from the narrow channels of the crystalline inclusion compounds (ICs) formed between the γ‐cyclodextrin (CD) host and PET and PC guests, which are reported for the first time. Differential scanning calorimetry, Fourier transform infrared, and X‐ray observations of PET and PC samples coalesced from their crystalline γ‐CD‐ICs suggest structures and morphologies that are different from those of samples obtained by ordinary solution and melt processing techniques. For example, as‐received PC is generally amorphous with a glass‐transition temperature (Tg) of about 150 °C; when cast from tetrahydrofuran solutions, PC is semicrystalline with a melting temperature (Tm) of about 230 °C; and after PC/γ‐CD‐IC is washed with hot water for the removal of the host γ‐CD and for the coalescence of the guest PC chains, it is semicrystalline but has an elevated Tm value of about 245 °C. PC crystals formed upon the coalescence of highly extended and segregated PC chains from the narrow channels in the γ‐CD host lattice are possibly more chain‐extended and certainly more stable than chain‐folded PC crystals grown from solution. Melting the PC crystals formed by coalescence from PC/γ‐CD‐IC produces a normal amorphous PC melt that, upon cooling, results in typical glassy PC. PET coalesced from its γ‐CD‐IC crystals, although also semicrystalline, displays a Tm value only marginally elevated from that of typical bulk or solution‐crystallized PET samples. However, after the melting of γ‐CD‐IC‐coalesced PET crystals, it is difficult to quench the resultant PET melt into the usual amorphous PET glass, characterized by a Tg value of about 80 °C. Instead, the coalesced PET melt rapidly recrystallizes during the attempted quench, and so upon reheating, it displays neither a Tg nor a crystallization exotherm but simply remelts at the as‐coalesced Tm. This behavior is unaffected by the coalesced PET sample being held above Tm for 2 h, indicating that the extended, unentangled nature of the chains in the noncrystalline regions of the coalesced PET are not easily converted into the completely disordered, randomly coiled, entangled melt. Apparently, the highly extended, unentangled characters of the PC and PET chains in their γ‐CD‐ICs are at least partially retained after they are coalesced. Initial differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared, and X‐ray observations are described here. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 992–1012, 2002

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