Digital light processing 3D printing of modified liquid isoprene rubber using thiol-click chemistry

This study highlights the additive manufacturing of diene-rubbers with digital light processing (DLP). The network formation relies on the crosslinking of a methacrylate-functional liquid isoprene rubber via photo-induced thiol-click chemistry. Bi-functional divinyl ethers are added as reactive diluents, which benefit from a low potential for skin irradiation and skin sensitization. Along with significantly reducing the viscosity, the divinyl ethers accelerate the cure kinetics of the diene-rubber across the main chain C[double bond, length as m-dash]C bonds of the isoprene units. Photo-DSC measurements reveal that the length of the glycol-spacer and the chemical structure (glycol versus alkyl) of the divinyl ether influence the photo-reactivity of the rubber formulations in thiol-ene reactions. In the present study, the highest reactivity is observed for tri(ethylene glycol) divinylether comprising a spacer with three glycol units. To improve the storage stability of the rubber formulation, a radical scavenger is applied to reduce premature crosslinking reactions under dark conditions. With the stabilized liquid rubber formulations, precise 3D structures with features of 0.5 mm are successfully manufactured with bottom-up DLP 3D printing.