Paramagnetic epoxy resin

Abstract

Abstract. This work illustrates that macrocycles can be used as crosslinking agents for curing epoxy resins, provided that they have appropriate organic functionalities. As macrocycles can complex metal ions in their structure, this curing reaction allows for the introduction of that metal ion into the resin network. As a result, some characteristic physical properties of the metallomacrocycle could be transferred to the new material. The bisphenol A diglycidyl ether (BADGE, n = 0) and hemin (a protoporphyrin IX containing the Fe(III) ion, and an additional chloride ligand) have been chosen. The new material has been characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier Transform Infrared (FT-IR), Nuclear Magnetic Resonance (NMR), Transmission Electron Microscopy (TEM), and magnetic susceptibility measurements). Fe(III) remains in the high-spin state during the curing process and, consequently, the final material exhibits the magnetic characteristics of hemin. The loss of the chlorine atom ligand during the cure of the resin allows that Fe(III) can act as Lewis acid, catalyzing the crosslinking reactions. At high BADGE n = 0/hemin ratios, the formation of ether and ester bonds occurs simultaneously during the process.

Crown ethers as new curing agents for epoxy resins

“…The maximum enthalpy change for all systems, except for the H 4 DOTA/epoxy system, corresponds to a stoichiometric ratio, since from this value the reaction enthalpies decrease when the proportion of epoxy increases. The behavior of H 4 DOTA is similar to that observed for hemin, since two possible reaction mechanisms (esterification and etherification) appear. This is directly related to the preparation of the sample since in this system we are working out of stoichiometric ratio (in epoxy excess).…”

“…The second one is to stabilize the transition state by hydrogen bonding with an acid curing agent, as well as strengthening the nucleophilic character of the acid, leading to a decrease in the energy barrier . The behavior of H 4 DOTA is very similar to hemin . In the case of hemin, Fe(III) catalyzed esterification reactions.…”

“…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 transferring some properties of the metal ion to the new material . 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 .…”

“…This allows for the introduction of a metal ion into the network structure, thus transferring some properties of the metal ion to the new material . 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 . 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.…”

New curing agents for epoxy resins: protoporphyrins

“…We have also demonstrated that the susceptibility of the new material obeys the Curie-Weiss law and that the Fe(III) ion inside the network structure of the BADGE (n = 0) resin remains in the high-spin state during the curing process. 2 Consequently, in the absence of friction, this modified resin is attracted by a magnetic field. In other words, the introduction of confined Fe(III) ion into the network structure of the BADGE (n = 0) resin transfers the paramagnetic characteristics of hemin 3 to the new material.…”