Thermochimica Acta 444 (2006) 57–64 Thermal stability of solid dispersions of naphthalene derivatives with -cyclodextrin and -cyclodextrin polymers ´ I˜ nigo X. Garc´ ıa-Zubiri, Gustavo Gonz´ alez-Gaitano, Jos´ e Ram ´ on Isasi ∗ Departamento de Qu´ ımica y Edafolog´ ıa, Facultad de Ciencias, Universidad de Navarra, 31080 Pamplona, Navarra, Spain Received 1 December 2005; received in revised form 14 February 2006; accepted 20 February 2006 Available online 6 March 2006 Abstract The thermal stabilities of some naphthalene derivatives (1-naphthyl acetate, 2-acetylnaphthalene, 1-naphthol) in -cyclodextrin (-CD) inclusion complexes and in -CD-containing polymeric systems (Poly-CD) have been studied using thermal and thermogravimetric analyses and infrared spectroscopy. In -CD systems, the stability of the 1-naphthyl acetate complex is lower than that of the 2-acetylnaphthalene complex, and both are more stable than the corresponding physical mixtures. For Poly-CD systems, the solid dispersions result much more stable than the corresponding -CD ones, both at room temperature and at 60 ◦ C. In the case of Poly-CD, besides the inclusion within CD cavities, the interaction of the guest with the crosslinking network confers an additional stability against volatilization. In contrast, an analogous crosslinked polymer prepared using sucrose instead of -CD does not retain noticeable amounts of the naphthalene derivatives. © 2006 Elsevier B.V. All rights reserved. Keywords: Cyclodextrins; Cyclodextrin polymers; Naphthalenes 1. Introduction Beta-cyclodextrin (-CD) is a torus-shaped natural cyclic oligosaccharide, having seven glucopyranose units linked by - 1,4-glycosidic bonds, with two hydrophilic rims and a cavity less polar than water. Its unusual structure gives the -CD the ability to form inclusion complexes, both in solution and in solid phase, through non-covalent interactions with molecules that fit into the cavity. The stability of such complexes is mainly attributed to van der Waals and hydrophobic interactions [1], although the substitution of a polar group in the guest compound can influ- ence the stability of the complex, by establishing either dipolar or hydrogen bonding interactions [1–3]. These inclusion com- plexes may confer desirable properties on the guest molecules such as an increased stability against hydrolysis or high tem- peratures, an enhanced aqueous solubility, and the masking of unpleasant tastes or odors of various chemicals. This encapsulat- ing ability has found countless applications in fields such as drug delivery, water purification, food industry, analytical methods, etc. [4]. ∗ Corresponding author. Tel.: +34 948 425600; fax: +34 948 425649. E-mail address: jrisasi@unav.es (J.R. Isasi). -CD can be crosslinked with polyfunctional reagents such as aldehydes, ketones, isocyanates or epoxides, to obtain water insoluble polymers that capture molecules from aqueous solu- tions. One of the most used crosslinking agents is epichlorohy- drin. The polymers synthesized by condensation between -CD and epichlorohydrin have been employed in many applications [5]. Because of their properties these polymers are used in sepa- ration columns for chromatography, in pharmaceutical and food industries, for synthetic purposes (in catalysis), for wastewa- ter treatment, etc. [6,7]. In this case, the sorption mechanism involves several kinds of interactions as proposed by several authors [7,8]. Besides the inclusion within -CD cavities, a physicochemical adsorption in the polymer network can also take place. Thermal analysis has been used as a tool in the character- ization of CDs and their inclusion complexes [9]. Among the different CDs, -CD is the most widely used because it pro- vides a better fit to a great variety of aromatic hydrocarbons and their derivatives. Its thermoanalytical profile can be structured in four stages: (1) water loss from ambient temperature up to 120 ◦ C (depending on the experimental arrangements: kind of crucible and lid, atmosphere...); (2) a plateau region; (3) thermal degradation, that starts above 250 ◦ C in solid phase and contin- ues for the liquid after fusion; (4) ignition, that takes place in air 0040-6031/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2006.02.024