Impact of magnetic ionic liquids as catalystson the curing process of epoxy/anhydride system: Mechanistic investigation and dynamic-mechanical analysis

Cyclic acid anhydride - based hardeners provide excellent physic-mechanical and thermal properties to epoxy networks. However, the curing process takes place at relatively high temperature, thus limiting the applications as coatings and free-heating devices. The present work describes for the first time the efficient catalytic action of imidazolium- and phosphonium- based ionic liquids (IL) bearing iron tetrachloride (FeCl4) as counteranion for the curing process of epoxy prepolymer (EP)/methyl tetrahydrophthalic anhydride (MTHPA) even at room temperature. Indeed, both differential scanning calorimetry and rheological analysis revealed that the addition of 5 phr of trihexyl (tetradecyl)-phosphonium iron tetrachloride (P-66614. FeCl4) resulted in faster curing process when compared with systems cured with conventional tertiary amine. The gelation at room temperature occurred before 24 h with this magnetic IL. Moreover, the systems catalyzed by P-66614. FeCl4 presented higher glass transition temperature, higher storage modulus and higher crosslink density as indicated by dynamic-mechanical analysis (DMA). A mechanism for the curing process was proposed based on DSC and Fourier transform infrared analysis. These results highlight the importance of magnetic ILs as catalysts for the curing process of EP/MTHPA system and open new avenues for applications of this system as a room temperature-based curing system.