Lithography-based additive manufacturing technologies (L-AMT) are based on photosensitive resins which can be cured by UV or visible light in a layer-based process. Parts printed by L-AMT show superior surface quality compared to other additive manufacturing technologies (AMT) due to the high optical resolution (e.g. 20 µm) and low layer thickness (e.g. 25 µm). L-AMT resins comprise multifunctional (meth)acrylate or epoxy systems which form highly crosslinked polymer materials. This leads to high stiffness and brittle fracturing of the final 3D-printed parts.
Chain transfer reagents can be used in radical photopolymerization of (meth)acrylate resins to regulate the polymer network resulting in increased toughness. Common formulations with chain transfer agents are based on a thiol-ene reaction and usually have bad odor and storage stability issues. These issues can be solved by addition fragmentation chain transfer (AFCT) based on beta-allyl sulfones. However, these beta-allyl sulfone AFCT have a negative influence on the reaction speed. New AFCT reagents based on vinyl sulfonate esters (EVS) have solved this issue.
Networks formed by AFCT reagents based on EVS show high network homogeneity, low shrinkage stress and significant increase in double bond conversion. The addition of 20 mol% EVS to a dimethacrylate formulation has improved impact resistance by a factor of ~5 without influencing the storage modulus at room temperature (~ 1 GPa). This formulation was also used to produce 3D-printed parts with high surface quality and at the same time good mechanical properties.