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 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.

Toughness enhancers for bone scaffold materials based on biocompatible photopolymers

“…A low t 95 is favorable for high printing speed, since the previous layer needs to be at a certain stability (i.e., conversion) to allow application of the following layer. F N is a measure for the developed shrinkage stress and should be as low as possible . Numerical data obtained through these measurements can be found in the Supporting Information (Table S1).…”

“…Since the gap size was held constant throughout the measurement, the resulting normal force (F N ) necessary to counteract polymer shrinkage during photopolymerization was measured and used as an indicator for shrinkage stress . The reference mixture developed a normal force around −21 N and mixtures containing PCL or DVC showed similar values.…”

“…Real‐time near‐infrared (RT‐NIR) photorheology was performed using an Anton Paar MCR302 WESP rheometer with a P‐PTD 200/GL Peltier glass plate and a PP25 measuring system, coupled with a Bruker VERTEX 80 FTIR spectrometer . The specific amount of formulation needed to fill the fixed 100 μm gap was determined empirically (63 μL).…”

Metallo‐Supramolecular Gels that are Photocleavable with Visible and Near‐Infrared Irradiation

“…To further investigate the de-gelation process,r eal-time-(RT)-photorheology experiments were carried out under visible-light irradiation. [22] Thestorage modulus G' of the gels was measured in oscillation mode (1 %, 2Hz) and then the samples were irradiated with visible light (400-500 nm, 10 mW cm À2 ). De-gelation of the organogel in MeCN was immediately detected upon irradiation by af ast decrease in modulus,r eaching af inal level after 10 si rradiation.…”

Durch sichtbares Licht und Nahinfrarotstrahlung abbaubare supramolekulare Metallo‐Gele

“…Zur weiteren Charakterisierung des Gelabbaus wurden Echtzeit-Photorheologie-Messungen [22] unter Bestrahlung mit Licht > 395 nm durchgeführt. Der Speichermodul G' der Gele wurde im Oszillationsmodus (1 %, 2Hz) gemessen, und anschließend wurde die Probe mit sichtbarem Licht (400-500 nm, 10 mW cm À2 )b estrahlt.…”