Tuning the physicochemical properties of β-cyclodextrin based polyurethanes via cross-linking conditions

• Polyurethane-based sorbents display unique structure and textural properties.
• Tunability was afforded by kinetic vs. thermodynamic addition of cross-linker.
• Polymer–dye sorption results afford structural and textural information.
• Structural variability is related to controlling the product reaction pathway.

Polyurethanes (PUs) were prepared by cross-linking β-cyclodextrin (β-CD) with two types of diisocyanates; hexamethylene diisocyanate and 4,4′-dicyclohexyl diisocyanate, respectively. Materials with diverse structural and textural properties were obtained by varying the rate of diisocyanate addition: rapid (R) or drop-wise (D; 0.1 mL/min). Characterization of the structural and textural properties was investigated by spectroscopic (1H NMR in solution, solid state 13C CP-MAS solids NMR, dynamic light scattering, UV–vis, and IR), thermogravimetric analysis, powder X-ray diffraction, and scanning electron microscopy. The accessibility of the β-CD inclusion sites of the polymers was independently evaluated using an equilibrium dye probe adsorption method with phenolphthalein, and a kinetic dye-based uptake method was studied in parallel using p-nitrophenol in aqueous solution. The characterization methods provide evidence that the drop-wise method affords polymer materials with greater cross-linking, as compared with the rapid addition method. Herein, we report the first example of a cross-linked polyurethane containing β-CD with tunable structure and physicochemical properties, according to the mode of cross-linker addition (R versus D) to control the reaction products.

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