Kinetic parameters for thermal decomposition of supramolecular polymers derived from flunixin-meglumine adducts Douglas L. Cassimiro • Clo ´vis A. Ribeiro • Jorge M. V. Capela • Marisa S. Crespi • Marisa V. Capela ESTAC2010 Conference Special Issue Ó Akade ´miai Kiado ´, Budapest, Hungary 2010 Abstract Meglumine, (2R,3R,4R,5S)-6-methylaminohex- ane-1,2,3,4,5-pentol, is a carbohydrate derived from sor- bitol in which the hydroxyl group in position one is replaced by a methylamine group. It forms binary adducts with substances having carboxyl groups, which have in common the presence of hydrogen bonding as the main force in the stabilization of these species. During melting, adducts of meglumine with flunixin (2-[[2-methyl-3-(tri- fluoromethyl)phenyl]amino]pyridine-3-carboxylic acid) poly- merize or self-assemble in amorphous supramolecular structures with molecular weights around 2.0 9 10 5 kDa. DSC curves, in a first heating, show isomorphic transitions where the last one at 137 °C for the flunixin-meglumine adduct originated the supramolecular amorphous polymers with glass transition around 49.5 °C. The kinetic parameters for the thermal decomposition step of the polymers were determined by the Capela-Ribeiro non-linear isoconver- sional method. From data for the TG curves in nitrogen atmosphere and heating rates of 5, 10, 15, and 20 °C min -1 , the E a and B a terms could be determined and, consequently, the pre-exponential factor, A a , as well as the kinetic model, g(a). Keywords Supramolecular polymers  Flunixin- meglumine  Adducts  Non-isothermal kinetics  Thermal decomposition Introduction Meglumine, (2R,3R,4R,5S)-6-methylaminohexane-1,2,3,4, 5-pentol, also known as N-methylglucamine, is a carbo- hydrate derived from sorbitol in which the hydroxyl group from position one is replaced by a methylamine group, as shown in Fig. 1. The increased applicability of meglumine lies in its ability to form adducts with carboxylic acids and markedly increases their solubility in aqueous solution, due to the large number of hydroxyl groups. This property has been extensively exploited by the phar- maceutical industry in the improvement of existing drugs, where the pharmacologically active substance is more soluble in water when taken in the form of an adduct with meglumine, without affecting the original activity of the drug in combi- nation. The most successful example of this approach involves the non-steroidal anti-inflammatory drugs (NSAIDs), which have terminal carboxylic acid groups [1–3]. The first study on adducts derived from the reaction between a carboxylic acid and meglumine did not elucidate the structure, since the major interest has always limited to increasing the solubility of NSAIDs in aqueous media. Some understanding about the structure of this class of binary species came only with the work of Cao et al. and Telang et al. [4, 5]. A more meaningful understanding of the structure of these adducts was obtained by X-ray diffraction (XRD) of a single crystal of the species generated by the reaction between flunixin, 2-[[2-methyl-3-(trifluoromethyl)phenyl] amino]pyridine-3-carboxylic acid, and meglumine, anionic and cationic components, respectively [4]. The adduct is primarily stabilized by hydrogen bonds between hydroxyl groups of the meglumine cation and the carboxylate of the flunixin anion (Fig. 2). D. L. Cassimiro  C. A. Ribeiro (&)  J. M. V. Capela  M. S. Crespi  M. V. Capela Institute of Chemistry, Paulista State University, Av. Prof. Francisco Degni, s/n, Araraquara, Sa ˜o Paulo 14800-900, Brazil e-mail: ribeiroc@iq.unesp.br 123 J Therm Anal Calorim (2011) 105:405–410 DOI 10.1007/s10973-010-1116-y