A new approach to producing tailored methacrylate-based photopolymers has been developed. This approach, which does not slow down the light curing process, could lead to tough photopolymers for 3D printing and biomedicine. The new approach by a team by at the Technical University of Vienna (TU Wien), led by professor Robert Liska, incorporates the use of an ester-activated vinyl sulfonate ester (EVS), which acts as a chain transfer agent. In the new approach, the chain transfer step induced by EVS reduces the kinetic chain length of the photopolymer, thus shifting the gel point to higher conversion, which results in reduced shrinkage stress and higher overall conversion. The resulting, more homogeneous network is responsible for the toughness of the material. Researchers attribute the ability of EVS to promote nearly retardation-free polymerization to the fact that after the transfer step, no polymerizable double bond is formed, as is usually seen in classical chain transfer agents. Current methods to control radical photopolymerization tend to slow the curing process. This is not ideal for applications such as 3D printing, which requires a short irradiation phase for high spatial resolution and economical production times. To test their photopolymer network, researchers prepared a scaffold-like sample structure using a methacrylate copolymer. Individual layers with a thickness of 50 μm were spatially well resolved. Laser flash photolysis, theoretical calculations, and photoreactor studies were used to elucidate the fast chain transfer reaction and exceptional regulating ability of EVS. Experiments showed that the material was homogenous, solid but elastic, and impact-resistant with high tensile strength. Researchers say these properties could be adjusted by changing the amount of EVS added. Without EVS, the material was very brittle. Final photopolymer networks exhibited improved mechanical performance, making EVS, in the opinion of the researchers, a strong candidate for the 3D printing of tough photopolymers for use in 3D printing, biomedicine, and microelectronics. The research was published in Angewandte Chemie International Edition (doi:10.1002/anie.201803747).