Monitoring of the Degree of Condensation in Alkoxysiloxane Layers by NIR Reflection Spectroscopy

This paper introduces a novel analytical approach for monitoring the degree of condensation of thin siloxane films, which is potentially suitable for in-line process control during the deposition of such layers, e.g., to polymer films. Near-infrared (NIR) reflection spectroscopy in combination with chemometric methods was used as a process monitoring tool. The state of the formation of the inorganic Si–O–Si network in partially condensed 3-methacryl­oxypropyl­trimeth­oxysilane batches was analyzed by inverse gated ²⁹Si NMR spectroscopy. Results were expressed in terms of different relative ratios of the Tⁱ species (i.e., structures with different numbers of Si–O–Si units per Si atom). These data were used for calibration of the NIR method, which was applied to thin layers printed on a polymer foil with a thickness of ∼2.2 g m^–2. The root-mean-square error of prediction (RMSEP) for the determination of the ratio of the Tⁱ species from the NIR spectra was found to be less than 3%. The error of the reference data from ²⁹Si NMR spectroscopy is 4%, which results in an overall error of 5%. Moreover, the thickness of siloxane layers was determined by this method in a range from 2.5 to 5.5 g m^–2 using gravimetry for calibration (prediction error ∼0.3 g m^–2)

A Straightforward Synthesis and Structure–Activity Relationship of Highly Efficient Initiators for Two-Photon Polymerization

The development of practical two-photon absorption photoinitiators (TPA PIs) has been slow due to their complicated syntheses often reliant on expensive catalysts. These shortcomings have been a critical obstruction for further advances in the promising field of two-photon-induced photopolymerization (TPIP) technology. This paper describes a series of linear and cyclic benzylidene ketone-based two-photon initiators containing double bonds and dialkylamino groups synthesized in one step via classical aldol condensation reactions. Systematic investigations of structure–activity relationships were conducted via quantum-chemical calculations and experimental tests. These results showed that the size of the central ring significantly affected the excited state energetics and emission quantum yields as well as the two-photon initiation efficiency. In the TPIP tests the 4-methylcyclohexanone-based initiator displayed much broader ideal processing windows than its counterparts with a central five-membered ring and previously described highly active TPA PIs. Surprisingly, a writing speed as high as 80 mm/s was obtained for the microfabrication of complex 3D structures employing acrylate-based formulations. These highly active TPA PIs also exhibit excellent thermal stability and remain inert to one-photon excitation. Straightforward synthesis combined with high TPA initiation efficiency makes these novel initiators promising candidates for commercialization

A Straightforward Synthesis and Structure–Activity Relationship of Highly Efficient Initiators for Two-Photon Polymerization

The development of practical two-photon absorption photoinitiators (TPA PIs) has been slow due to their complicated syntheses often reliant on expensive catalysts. These shortcomings have been a critical obstruction for further advances in the promising field of two-photon-induced photopolymerization (TPIP) technology. This paper describes a series of linear and cyclic benzylidene ketone-based two-photon initiators containing double bonds and dialkylamino groups synthesized in one step via classical aldol condensation reactions. Systematic investigations of structure–activity relationships were conducted via quantum-chemical calculations and experimental tests. These results showed that the size of the central ring significantly affected the excited state energetics and emission quantum yields as well as the two-photon initiation efficiency. In the TPIP tests the 4-methylcyclohexanone-based initiator displayed much broader ideal processing windows than its counterparts with a central five-membered ring and previously described highly active TPA PIs. Surprisingly, a writing speed as high as 80 mm/s was obtained for the microfabrication of complex 3D structures employing acrylate-based formulations. These highly active TPA PIs also exhibit excellent thermal stability and remain inert to one-photon excitation. Straightforward synthesis combined with high TPA initiation efficiency makes these novel initiators promising candidates for commercialization