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.

Wide-angle X-ray scattering observations of alpha-cyclodextrin (CD)-poly(ethylene glycol) (PEG) inclusion complexes (ICs) have shown for the first time that two crystalline columnar modifications (forms I and II) are produced in the process of their formation. This was made possible by precise azimuthal X-ray diffraction scanning of oriented IC samples. Form I is characterized by CDs threaded onto PEG chains and arranged along channels in the order head-to-head/tail-to-tail, while form II is formed by unbound CDs also arranged into columns in a head-to-tail and also possibly a head-to-head/tail-to-tail manner, probably as a result of template crystallization on the form I IC crystals. It was shown that similar structural peculiarities are inherent for channel structures based on ICs obtained with PEG with a wide range of molecular weights (MWs). The characteristic feature of ICs based on PEG, especially with MW > 8000, is the presence of unbound polymer in the composition of the complex. The amount of unbound PEG was shown to rise with increasing MW of PEG, resulting in greater imperfections in the IC crystalline structure. The polyblock structure of ICs based on alpha-CD and PEG was therefore proposed.

Introduction. Aliphatic polyesters represent an important family of biodegradable materials. Increasing attention has been focused on hydrolytically unstable lactone polymers owing to their usefulness in biomedical applications.To enhance the rate of biodegradation, the permeability and the tensile properties of the biomaterials, copolymerization, and blending processes have been used. Blending with other biodegradable polymers might offer a more cost-effective way of modifying the properties of hard and brittle poly(L-lactic acid) (PLLA) than chemical modification. 1,2 Previously, several blend systems containing PLLA have been investigated, such as PLLA/poly(ethylene oxide) (PEO), 3,4 PLLA/poly(DLlactide) (PDLLA), 5-7 PLLA/PEO-poly(propylene oxide)-PEO copolymers, 8 PLLA/poly(3-hydroxybutyrate) (PHB), 9 PLLA/poly( -caprolactone) (PCL), 9 and PLLA/poly(pvinylphenol) PVPh. 10 However, most of the blends were found to be immiscible, including a phase-separated morphology identified for PLLA/PCL blends. 9 Taking advantage of the ability of R-cyclodextrin (R-CD) to form inclusion compounds (ICs) with both PLLA and PCL, an intimately compatible blend can be achieved when PLLA/PCL-R-CD IC was obtained and afterward washed with a solvent (H 2 O) for the R-CD host, which is a nonsolvent for the guest polymers.Recently, we have reported that R-CD forms a crystalline IC with high molecular weight PCL. 11 Here, we have also found that R-CD can form complexes with PLLA (M w ) 285 000), as well as simultaneously with PLLA and PCL.The miscibility of the PLLA/PCL blend extracted from R-CD IC channels has been investigated by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and polarizing optical microscopy. These preliminary results are compared to those of a PLLA/PCL blend cast from their common solution in dioxane.Experimental Section. a. r-CD IC Formation. A heated solution (50 °C) of PCL (0.4 g, 3.5 mmol in monomer unit, M w ) 65 000) and PLLA (0.25 g, 3.5 mmol in monomer unit, M w ) 285 000) in dioxane (200 mL) was slowly added to 50 mL of an aqueous solution saturated with R-CD (7.25 g, 7.5 mmol) also held at 50 °C. After 1 h of stirring at 50 °C, the solution was allowed to cool to room temperature while continuously stirring for another 24 h. A white powder was collected