Vat Photopolymerization of Synthetic Isoprene Rubber Latexes

Isoprene-based elastomers comprise a large percentage of the traditional elastomer market with broad technological impact; however, the challenge of three-dimensional (3D) printing intricate geometries using synthetic isoprene rubbers remains elusive. This manuscript reports synthetic isoprene rubber (SIR) latexes as a precursor for the unprecedented 3D printing of high-molecular-weight isoprene-based elastomers with vat photopolymerization (VP). Dispersed SIR latex particles at 900 nm mitigate entanglement of high-molecular-weight SIR and thus provide low viscosities, which are aligned with viscosity requirements (<10 Pa·s) for VP. The incorporation of reactive monomers, i.e., 1-vinyl-2-pyrrolidone (NVP) and poly(ethylene glycol) diacrylate (PEGDA), into the aqueous phase enables the rapid photopolymerization forming a hydrogel scaffold embedded with SIR particles. Subsequent thermal postprocessing of the photocured hydrogel green bodies promotes SIR particle coalescence through the photogenerated scaffold resulting in a semi-interpenetrating network (sIPN) that exhibits isotropic shrinkage while preserving structural fidelity. Variation in the scaffold concentration tuned the elastomeric properties of the photocured SIR with elongations at break ranging from 94 to 682%. The resulting elastomers exhibit multiphase morphologies and elastomeric properties for a variety of 3D geometric structures.