title: Real Time-NIR/MIR-Photorheology: A Versatile Tool for the in Situ Characterization of Photopolymerization Reactions.
abstract: 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 CaF2window 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.
authors.affiliation: Institute of Applied Synthetic Chemistry , Technische Universität Wien, Getreidemarkt 9/163 MC, 1060 Vienna, Austria.|Christian-Doppler-Laboratory for Photopolymers in Digital and Restorative Dentistry , Getreidemarkt 9, 1060 Vienna, Austria.
authors.forename: Christian
authors.identifier: 0000-0002-6374-3595
authors.initials: C
authors.lastname: Gorsche
authors.affiliation: Institute of Applied Synthetic Chemistry , Technische Universität Wien, Getreidemarkt 9/163 MC, 1060 Vienna, Austria.|Christian-Doppler-Laboratory for Photopolymers in Digital and Restorative Dentistry , Getreidemarkt 9, 1060 Vienna, Austria.
authors.forename: Reghunathan
authors.initials: R
authors.lastname: Harikrishna
authors.affiliation: Institute of Applied Synthetic Chemistry , Technische Universität Wien, Getreidemarkt 9/163 MC, 1060 Vienna, Austria.
authors.forename: Stefan
authors.initials: S
authors.lastname: Baudis
authors.affiliation: Institute of Applied Synthetic Chemistry , Technische Universität Wien, Getreidemarkt 9/163 MC, 1060 Vienna, Austria.
authors.forename: Patrick
authors.initials: P
authors.lastname: Knaack
authors.affiliation: Institute of Applied Synthetic Chemistry , Technische Universität Wien, Getreidemarkt 9/163 MC, 1060 Vienna, Austria.
authors.forename: Branislav
authors.initials: B
authors.lastname: Husar
authors.affiliation: Anton Paar Germany GmbH , Helmuth-Hirth-Strasse 6, D-73760 Ostfildern, Germany.
authors.forename: Joerg
authors.initials: J
authors.lastname: Laeuger
authors.affiliation: Institute of Applied Synthetic Chemistry , Technische Universität Wien, Getreidemarkt 9/163 MC, 1060 Vienna, Austria.
authors.forename: Helmuth
authors.initials: H
authors.lastname: Hoffmann
authors.affiliation: Institute of Applied Synthetic Chemistry , Technische Universität Wien, Getreidemarkt 9/163 MC, 1060 Vienna, Austria.|Christian-Doppler-Laboratory for Photopolymers in Digital and Restorative Dentistry , Getreidemarkt 9, 1060 Vienna, Austria.
authors.forename: Robert
authors.identifier: 0000-0001-7865-1936
authors.initials: R
authors.lastname: Liska