Polymer Communication Formation and characterization of thiourea encapsulated polyethylene oxide Astrid Campo a , Juli Fretti b , Nadarajah Vasanthan a, * a Department of Chemistry, Long Island University, One University Plaza, Brooklyn, NY 11201, United States b Department of Material Science, Ecole Polytechnique de I’ Universite’ de Nantes, Nantes, France Received 13 October 2007; received in revised form 30 November 2007; accepted 9 December 2007 Available online 15 December 2007 Abstract The structure and dynamics of PEO chains encapsulated in thiourea (TU) channels formed in the PEOeTU-inclusion compound (PEOeTU-IC) were studied by XRD, FTIR and solid state NMR spectroscopy. XRD and FTIR observations clearly show PEOeTU-IC adopts a crystal struc- ture different from neat thiourea, and the usual rhombohedral crystal structure of thiourea small molecule ICs. PEO chains in the channel adopt a conformation similar to bulk PEO, as confirmed by solid state NMR spectroscopy. Contact-time array (VCT) NMR profiles shows that PEO chains in the TU channels are considerably more mobile than in bulk PEO. Infrared bands for the PEO shift in the IC, and these were attributed to changes in the secondary forces. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Polyethylene oxide; Encapsulation; Thiourea 1. Introduction Supramolecular chemistry is often pursued to develop new material functions, such as magnetic properties, light respon- siveness, catalytic activity, self-healing polymers, and chemi- cal sensors that cannot be obtained from a single molecule [1]. Hosteguest chemistry, a class of supramolecular chemis- try, describes complexes that are composed of two or more molecules or ions held together by secondary forces, such as hydrogen bonding or by van der Waals forces [2,3]. An inclu- sion compound is a complex in which one component forms a cavity (host) where a second component (guest ¼ alkanes, cyclic alkanes, and macromolecules, etc.) resides. Urea [4], thiourea [5], and cyclodextrins [6] are known to form inclusion compounds with a variety of organic guest molecules. The dynamics and conformations of polymer guests that have been encapsulated in urea [7] and cyclodextrin [8] hosts were studied extensively by Tonelli and coworkers. Urea forms host clathrate channels with a diameter of 5.5 A ˚ , while thiourea forms larger channels with an approximately 7 A ˚ diameter. Thiourea can accommodate aromatic rings as well as branched aliphatic compounds, while urea can accommodate only linear aliphatic chains. Thiourea channels have prominent bulges (di- ameter 7.1 A ˚ ) and constrictions (diameter 5.8 A ˚ ) at different positions along the channel, similar to Zeolites [9]. Therefore thiourea inclusion compounds have attracted a great deal of interest. For the first time PEO was encapsulated in thiourea channels (PEOeTU-IC) and structural details of the IC and the mobility of the guest PEO chains are discussed here. 2. Experimental A physical mixture of thiourea (1 g) and PEO (0.144 g), which corresponds to 4:1 molar ratio, was prepared. The phys- ical mixture was heated in an oven preset at 80  C about 1 h. A white powdery sample appeared after 1 h. The product was allowed to cool to room temperature and saved in a desiccator for further analysis. Wide angle X-ray diffraction of powder samples was obtained using a SCINTAG XGEN-400 at room temperature. * Corresponding author. Tel.: þ1 718 246 6328; fax: þ1 718 488 1465. E-mail address: nadarajah.vasanthan@liu.edu (N. Vasanthan). 0032-3861/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2007.12.008 Available online at www.sciencedirect.com Polymer 49 (2008) 374e377 www.elsevier.com/locate/polymer