In photopolymerization reactions, mostly multifunctional monomers are employed, as they ensure fast reaction times and good final mechanical properties of the cured materials. Drawing conclusions about the influence of the components and curing conditions on the mechanical properties of the subsequently formed insoluble networks is challenging. Therefore, an in situ observation of chemical and mechanical characteristics during the photopolymerization reaction is desired. By coupling of an infrared spectrometer with a photorheometer, a broad spectrum of different photopolymerizable formulations can be analyzed during the curing reaction. The rheological information (i.e., time to gelation, final modulus, shrinkage force) can be derived from a parallel plate rheometer equipped with a UV- and IR-translucent window (glass for NIR and CaF window for MIR). Chemical information (i.e., conversion at the gel point and final conversion) is gained by monitoring the decrease of the corresponding IR-peak for the reactive monomer unit (e.g., C═C double bond peak for (meth)acrylates, H-S thiol and C═C double bond peak in thiol-ene systems, C-O epoxy peak for epoxy resins). Depending on the relative concentration of reactive functional groups in the sample volume and the intensity of the IR signal, the conversion can be monitored in the near-infrared region (e.g., acrylate double bonds, epoxy groups) or the MIR region (e.g., thiol signal). Moreover, an integrated Peltier element and external heating hood enable the characterization of photopolymerization reactions at elevated temperatures, which also widens the window of application to resins that are waxy or solid at ambient conditions. By switching from water to heavy water, the chemical conversion during photopolymerization of hydrogel precursor formulations can also be examined. Moreover, this device could also represent an analytical tool for a variety of thermally and redox initiated systems.

The formation of networks through light-initiated radical polymerization allows little freedom for tailored network design. The resulting inhomogeneous network architectures and brittle material behavior of such glassy-type networks limit the commercial application of photopolymers in 3D printing, biomedicine, and microelectronics. An ester-activated vinyl sulfonate ester (EVS) is presented for the rapid formation of tailored methacrylate-based networks. 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 high toughness of the material. The unique property of EVS to promote nearly retardation-free polymerization can be attributed to the fact that after the transfer step no polymerizable double bond is formed, as is usually seen in classical chain transfer agents. Laser flash photolysis, theoretical calculations, and photoreactor studies were used to elucidate the fast chain transfer reaction and exceptional regulating ability of EVS. Final photopolymer networks exhibit improved mechanical performance making EVS an outstanding candidate for the 3D printing of tough photopolymers.

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Die Netzwerkbildung während der lichtinitiierten radikalischen Polymerisation erfolgt ungeregelt und ist nicht einfach zu kontrollieren. Die entstehenden Photopolymere besitzen eine inhomogene Netzwerkarchitektur, welche in sprödem Materialverhalten resultiert und somit die Anwendung beispielsweise für den 3D‐Druck, Biomedizin und Mikroelektronik limitiert. In dieser Arbeit wird ein Ester‐aktivierter Vinylsulfonatester (EVS) präsentiert, der die schnelle Bildung von geregelten Methacrylat‐basierten Netzwerken ermöglicht. Der durch EVS eingeleitete Kettenübertragungsschritt reduziert die kinetische Kettenlänge des Photopolymers und verschiebt den Gelpunkt zu höheren Umsätzen. Dies hat eine geringere polymerisationsinduzierte Schrumpfspannung und einen höheren Gesamtumsatz zur Folge. Das gebildete gleichmäßigere Polymernetzwerk ist der Grund für die hohe Zähigkeit des Endmaterials. Die einzigartige Fähigkeit von EVS zur nahezu verzögerungsfreien Polymerisation basiert auf der Tatsache, dass nach dem Kettenübertragungsschritt keine Doppelbindung gebildet wird, die weiterreagieren könnte. Laser‐Blitzlichtphotolyse, theoretische Berechnungen und Photoreaktorstudien machen den schnellen Kettenübertragungsschritt und die außergewöhnlichen Netzwerkregelungseigenschaften von EVS verständlich. Die resultierenden Polymere weisen verbesserte mechanische Eigenschaften auf, was EVS zu einem ausgezeichneten Kandidaten für den lithographiebasierten 3D‐Druck von zähen Photopolymeren macht.