# Development of Inkjet Printable Formulations Based on Polyorganosilazane and Divinylbenzene
## 3 Results and Discussion
### Crosslinking Behavior and FTIR Analysis  
The FTIR analysis was performed to study the crosslinking behavior of the UV- cured samples and their resulting chemical structure. Figure 3 shows the FTIR spectra of the liquid and uncured DVB15 and of all crosslinked samples with an increasing amount of DVB. The assignment of the peaks was conducted in accordance with the literature [54]. As already described in our previous work [14], the stretching vibrations of the N-H and Si-H bonds (3382 and 2135 cm\({}^{-1}\)), respectively, and the stretching and the deformation vibration of the vinyl groups (3046 and 1595 cm\({}^{-1}\)) are responsible for the crosslinking process in OPSZ. The spectra of the UV-cured samples show that bands corresponding to the vinyl group decrease and, in some cases, disappear, which is attributable to the radical polymerization of the vinyl groups in OPSZ and DVB [46; 48]. The radicals of the photo initiator activate the vinyl groups in DVB and OPSZ and initiate the polymerization, where DVB monomers can be integrated into the OPSZ crosslinking network. As Figure 3 shows, the bands of the stretching vibrations of the N-H and Si-H bonds at 3382 cm\({}^{-1}\) and 2135 cm\({}^{-1}\), respectively, remain after UV polymerization implying an incomplete crosslinking of the system. For this reason, the thermal initiator DCP was added to the formulations to post-cure the samples during the pyrolysis process in a nitrogen atmosphere. For this curing step, a dwell time of 30 min at 150 \({}^{\circ}\)C was set and afterwards, a slow heating rate of 1 \({}^{\circ}\)C/min was adjusted to enable transamination and dehydrocoupling reactions. The crosslinking behavior was studied by taking a closer look at the reactive vinyl group. The relative degree of conversion DC (%) of the reactive vinyl group was calculated as described in our previous work [14]. As a reference, the sharp band of Si-CH\({}_{3}\) at 1256 cm\({}^{-1}\) was taken, since it is a characteristic band for OPSZ and is not involved in the crosslinking process. Table 3 summarizes the results of the degree of conversion and they are as high as 83%, indicating free-radical polymerization of vinyl groups during the crosslinking process induced by the LED source (\(\lambda_{\text{max}}\) = 385 nm). This result is evident in the spectra (Figure 3) since the band of the vinyl group at 1595 cm\({}^{-1}\) decreases for all cured samples. The results for the degree of conversion of the Si-H and N-H bonds were neglected because their calculation from the spectra could not be performed with certainty for all samples. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Surface Tension** & **Contact Angle on** & \multirow{2}{*}{**Viscosity at 500 s\({}^{-1}\)**} \\  & **(mN/m)** & & **Silicon Wafer** \\  & & **(\({}^{\circ}\))** & **(mPa-s)** \\ \hline DVB0 & 21 & 5 & 30 \\ DVB15 & 24.7 & 5 & 21 \\ DVB30 & 24.2 & 3 & 9.5 \\ DVB45 & 24.9 & Spreading & 7 \\ DVB60 & 24.6 & 3 & 3.7 \\ DVB75 & 26.4 & Spreading & 2.5 \\ DVB100 & 30.55 & - & 1.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Results of the surface tension, wetting, and rheological behavior at the highest shear rate of all samples. Figure 4 shows the plotting of the FTIR spectra of the uncured, the cured, and the pyrolyzed samples of the formulation DVB15. The bands of the organic bonds disappear after pyrolysis at 1100 \({}^{\circ}\)C due to a complete polymer to ceramic conversion. The ceramization process leads to an amorphous ceramic network at the given temperature. The broad band between 1250 and 600 cm\({}^{-1}\) remained present corresponding to Si-O-Si, Si-N-Si, and Si-C bonds. The presence of oxygen in the amorphous ceramic is due to the sensitivity of OPSZ to moisture leading to hydrolysis and polycondensation reaction [55]. Within this work, it cannot be prevented because the samples were prepared in an ambient atmosphere.