Research Article Received: 12 May 2017 Revised: 21 September 2017 Accepted article published: 26 September 2017 Published online in Wiley Online Library: (wileyonlinelibrary.com) DOI 10.1002/pi.5476 Crown ethers as new curing agents for epoxy resins Francisco Fraga López, * Eva C Vázquez Barreiro, Aida Jover, José Manuel Martínez Ageitos, Eugenio Rodríguez and José Vázquez Tato Abstract Different crown ethers (4-aminobenzo-15-crown-5 (4-aminobenzo-15-C5), 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (diaza-18-crown-6), tetraazacyclododecane-1,4,7,10-tetraacetic acid (H 4 DOTA) and tetraazacyclododecane-1,4,7,10- tetraacetamide (H 2 ODDA)) were used as curing agent for bisphenol A diglycidyl ether (BADGE, n = 0). The maximum enthalpy change for all systems except that formed by the epoxy resin with H 4 DOTA corresponds to a stoichiometric ratio, since from this value the reaction enthalpies decrease when the proportion of epoxy increases. Heteropolymerization reaction occurs in all the crown ethers. Etherification reactions occur at temperatures much lower (30 ∘ C less) than for the porphyrin systems studied in which a second signal appears at 300 ∘ C. The etherification is evidenced by a slight shoulder in the thermograms for H 4 DOTA and H 2 ODDA. The systems BADGE (n = 0)/4-aminobenzo-15-C5 and BADGE (n = 0)/diaza-18-crown-6 improve the thermal stability of the epoxy resin by 30 ∘ C approximately while the improvement for BADGE (n = 0)/H 4 DOTA and BADGE (n = 0)/H 2 ODDA is about 60 ∘ C. © 2017 Society of Chemical Industry Keywords: crown ethers; epoxy resin; etherification; esterification INTRODUCTION Crown ethers are macrocycles that have the intrinsic ability to com- plex ions or small organic molecules and selectively extract these species from aqueous media. The influence of the physical proper- ties of the solvent, the ring size of the crown ether with respect to the ion size, the number and type of donor atoms (closely linked with the ring size), the flexibility of the ring, the substituents, the nature of the cation and the electron density of the ring cav- ity are factors to consider in the formation of the complexes. 1 Crown ethers have an important role in many applications includ- ing the solubilization of alkali metals or inorganic salts in apolar aprotic and polar solvents; the catalysis of organic reactions, in homogeneous phase, liquid–liquid solid–liquid phase; the sepa- ration or concentration of alkali or alkaline metal cations; the cap- ture, recovery, separation, concentration or purification of noble or heavy metals; selective electrode sensors; the determination of specific metals; and for ionophore transport across membranes in biochemistry and biophysics (such as for example the natural ionophores valinomycin and nonactin). 2 - 5 They are also very use- ful as switches that allow new devices to be created for detect- ing and controlling separation (by photoinduction, redox, pH or thermal). 6 In the medical field, the crown ethers are used in clinical analysis as therapeutic and diagnostic agents. 7 These compounds are used as diagnostic agents in the human body to help locate a tumor by magnetic resonance imaging. They have also been used successfully as administrators of therapeutic agents to help elim- inate toxins from the human body or to help to cure diseased tis- sues. The crown ethers are used in the semiconductor industry and in liquid crystals. In previous papers, we have demonstrated that macrocycles can be used as crosslinking agents for curing the bisphenol A diglycidyl ether (BADGE; n = 0) epoxy resin. This allows for the introduction of a metal ion into the network structure, thus trans- ferring some properties of the metal ion to the new material. 8,9 For instance, the Fe(III) ion of hemin, used for curing the epoxy resin BADGE (n = 0), remains in the high-spin state during the curing process and consequently the new material exhibits the paramagnetic characteristics of hemin obeying the Curie–Weiss law. 9 Since crown ethers are good complexing agents of metal ions they can also be used for that purpose, provided that they have appropriate organic groups for the required curing reactions. In this paper, four crown ethers (Fig. 1: 4-aminobenzo-15-crown- 5 (4-aminobenzo-15-C5), 1,4,10,13-tetraoxa-7,16-diazacycloocta decane (diaza-18-crown-6), tetraazacyclododecane-1,4,7,10-tetra- acetic acid (H 4 DOTA) and 4,4’-(1,4,10,13-tetraoxa-7,16-diazacyclo- octadecane-7,16-diyl)bis(4-oxobutanoic acid) (H 2 ODDA)) were used as curing agents for BADGE (n = 0) epoxy resin. The first three compounds are commercially available and the third one has been synthesized. Two ether crowns have amine groups as reacting sites while the other two have carboxy- late groups. By using protoporphyrin IX we have recently demonstrated that carboxylate groups, linked to macrocy- cle compounds, are good crosslinking organic functions 10 of the resin. ∗ Correspondence to: F Fraga López, Facultad de Ciencias, Departamentos de Física Aplicada y Química Física, Campus de Lugo, Universidad de Santiago de Compostela, Spain. E-mail: francisco.fraga@usc.es Facultad de Ciencias, Departamentos de Física Aplicada y Química Física, Campus de Lugo, Universidad de Santiago de Compostela, Spain Polym Int (2017) www.soci.org © 2017 Society of Chemical Industry