"Dissolve-on-Demand" 3D Printed Materials: Polymerizable Eutectics for Generating High Modulus, Thermoresponsive and...

Solvent-free photopolymerization of vinyl monomers to produce high modulus materials with applications in 3D printing and photoswitchable materials is demonstrated. Polymerizable eutectic (PE) mixtures are prepared by simply heating and stirring various molar ratios of N-isopropylacrylamide (NIPAM), acrylamide (AAm) and 2-hydroxyethyl methacrylate (HEMA). The structural and thermal properties of the resulting mixtures are evaluated by 1D and 2D NMR spectroscopy as well as differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). UV photocuring kinetics of the PE mixtures is evaluated via in situ photo-DSC and photorheology measurements. The PE mixtures cure rapidly and display storage moduli that are orders of magnitude greater than equivalent copolymers cured in an aqueous medium. The versatility of these PE systems is demonstrated through the addition of a photoswitchable spiropyran acrylate monomer, as well as applying the PE formulation as a stereolithography (SLA)-based 3D printing resin. Due to the hydrogen-bonding network in PE systems, 3D printing of the eutectic resin is possible in the absence of crosslinkers. The addition of a RAFT agent to reduce average polymer chain length enables 3D printing of materials which retain their shape and can be dissolved on demand in appropriate solvents.