The Effects of Ionic Liquid Addition on the Heat of Polymerization of Additive Manufacturing Resins

Abstract

Ionic liquids (ILs) are utilized for a wide range of applications today due to their low vapor pressure, near infinite combination of cations and anions with varying chemical functionalities, organic and inorganic species solubility, as well as their superb thermal and chemical stabilities. In this work, four ILs are used as additives for 3D printing resins to add flexibility to the final printed parts. The ILs of interest are 1-n-butyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide ([C4mim][NTf2]) and 2-(1-methylimidazolium)-ethyl methacrylate chloride ([mimEMA][Cl]), which were synthesized in-house, as well as tetraethylammonium bis(trifluoromethanesulfonyl)imide ([TEA][NTf2]) and Butyltrimethylammonium bis(trifluoromethanesulfonyl)imide ([BTMA][NTf2], which were purchased and used as received. These ILs were added to commercial Formlabs CV4 resin from 10 to 50 wt%. The change in temperature of polymerization is characterized via container-less acoustic levitation and FLIR thermography and the heat capacity is characterized with differential scanning calorimetry (DSC). From these two measurements, the enthalpy of polymerization was calculated via a simple equation relating the change in droplet temperature to the reaction enthalpy equation and compared to literature values. The degradation temperature of each was also characterized via thermal gravimetric analysis (TGA). Each IL lowered the enthalpy of polymerization while the substances with [NTf2] counterions raised the decomposition temperature and the only substance containing Cl anions, [mimEMA][Cl], lowered the decomposition temperature.