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.

Thermal bulk curing of epoxy resins is a non-energy efficient method. On the other hand classical photocuring techniques for epoxy resins are limited to quite thin layers, due to the limited penetration depth of UV-light. We show that Radical Induced Cationic Frontal Polymerization (RICFP) is a promising technique for the energy efficient bulk curing of epoxy resins. The combination of a C-C labile compound (1,1,2,2tetraphenylethanediol) as a thermal radical initiator with diaryliodonium salts results upon local thermalor photoinitiation in a self-sustaining front moving along the formulation and curing cationically curable resins completely. This allows the curing of monomer formulations in places that are not easily accessible or on objects that cannot be thermally cured because of their thermal instability or size. In this paper we report about first basic investigations on RICFP of several epoxy resins with C-C-labile compounds and compare them to common thermal radical initiators. Fig. 1 Structure of the bisphenol A diglycidylether resin (BADGE). † Electronic supplementary information (ESI) available. See

Radical induced cationic frontal polymerization (RICFP) is an extremely powerful and elegant alternative curing technique that allows cationic bulk curing of epoxy resins with very little energy consumption, as well as curing in compartments that are not readily accessible. We recently introduced a bisphenol‐A diglycidylether (BADGE) based system that allows the bubble‐free photocuring of this widely used epoxy resin. In this article, we describe the high storage stability and possibilities to influence the curing speed via the initiator concentrations of different formulations. These properties allow the adjustment of the frontal polymerization to ones need. We also show that the (thermo)mechanical and electrical properties of frontal cured epoxy polymers compares favorably with those of state of the art material. Finally, different strategies to overcome the challenges on producing epoxy resin based mica composites via RICFP are presented. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3751–3759

Novel cationic photoinitiators based on the non-nucleophilic [Al(OC(CF3)3)4]− anion were prepared and their high efficiency was presented in comparison to benchmark systems.

Vinyl sulfone esters are described as a new class of AFCT reagents for methacrylate-based photopolymerization without the drawback of retardation but good regulation of network architecture. Resulting materials show low shrinkage stress and increased toughness. This paves the way for vinyl sulfone esters in lithography-based 3D printing.