Preparation and Characterization of a Polymer-Based “Molecular Accordion” Abdalla H. Karoyo and Lee D. Wilson* Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, SK S7N 5C9, Canada * S Supporting Information ABSTRACT: A urethane-based polymer material, denoted HDI-1, was obtained from the addition reaction of β- cyclodextrin (β-CD) with 1,6-hexamethylene diisocyanate (HDI) at the 1:1 mole ratio. In aqueous solution and ambient temperature conditions, HDI-1 adopts a compact (coiled) morphology where the cross-linker units become coiled and are partially self-included in the annular hydroxyl (interstitial) region of β-CD. As the temperature is raised or as p-nitrophenol (PNP) was included within the β-CD cavity and the noninclusion sites of the polymer, an extended (uncoiled) morphology was adopted. The equilibrium distribution between the extended and the compact forms of HDI-1 is thermally and chemically switchable, in accordance with the hydration properties and host-guest chemistry of this responsive polymer system. The molecular structure of this water-soluble urethane polymer and its host-guest complexes with PNP were investigated using spectroscopic (Raman, 1 H NMR, induced circular dichroism), dynamic light scattering (DLS), and calorimetric (DSC) methods in aqueous solution at ambient pH, and compared with native β-CD. This study reports on the unique supramolecular properties of a polymer that resembles a thermally and chemically responsive “molecular accordion”. ■ INTRODUCTION The use of polymers, colloids, and supramolecular tectons as porogens in nanocasting strategies yields a wide variety of novel imprinted porous materials. 1-3 By analogy, the development of macromolecular porous materials with tunable morphology, textural parameters, and physicochemical properties is possible by embedding a macrocyclic porogen into a cross-linked polymer framework. Cyclodextrins (CDs) such as α-, β-, and γ- CDs are among the most widely studied macrocyclic host compounds, in part, due to their remarkable ability to form inclusion complexes with a diverse range of organic guest molecules in condensed phases and gaseous states. 4, 5 Incorporation of β-CD within a polymer framework represents a modular design approach with significant potential for the controlled tuning of the molecular recognition properties of functional macromolecular materials. 6-8 Supramolecular self-assembly that is accompanied by structure and property changes in response to external stimuli is shown by an emerging class of “smart” or “f unctional” porous materials with improved solid phase extraction (SPE) and molecular recognition properties. 4,8-14 The introduction of temperature sensitive compounds such as polyacrylamides (PAMs) and oligo(ethylene glycol)s (OEGs) into polymers and low molar mass scaffolds has been widely reviewed as the main strategy for preparing thermoresponsive smart materi- als. 15-20 As well, azobenzenes have been widely used as macromolecular prepolymers for photosensitive materials due to their ability to undergo reversible isomerization from a linear and flat E-form to a more compact and kinked Z-form upon UV and visible light irradiation. 21-23 The use of CDs as porogenic components for “smart” polymer materials is important in various fields ranging from separation and adsorption science to advanced drug delivery systems. The sorption and host/guest recognition properties of CD-based polymers 3,8,12,15 are influenced by the surface area, pore structure, and the relative accessibility of the binding sites (i.e., inclusion and interstitial) of the polymer framework. Inclusion site accessibility for polymers containing β-CD is essential for the formation of well-defined host/guest inclusion complexes. 24-26 CD-based polymers are known to display tunable physicochemical properties that extend the range of conventional sorbent materials. 3,13,27 The sorption properties of β-CD urethane polymers reveal that the adsorbent surface structure may provide multiple binding sites for adsorbates via the inclusion and noninclusion (interstitial) sites with variable hydrophile-lipophile characteristics. Thus, rational adsorbent design accounts for the inclusion site accessibility of β-CD and the role of the interstitial framework domains via tuning the cross-link density of the polymer by selection of a cross-linker agent with suitable physicochemical properties. 12,26,27 Received: January 14, 2016 Revised: March 1, 2016 Published: March 2, 2016 Article pubs.acs.org/Langmuir © 2016 American Chemical Society 3066 DOI: 10.1021/acs.langmuir.6b00099 Langmuir 2016, 32, 3066-3078 Downloaded via UNIV OF SASKATCHEWAN on July 20, 2019 at 17:29:01 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.