Effect of ambient atmosphere on crosslinking of polysilazanes

Abstract

The influence of ambient atmosphere on the crosslinking process of two commercially available polysilazanes with different molecular units in the backbone structure (one polysilazane with and one without urea units) was studied at different temperatures using oscillatory rheometry under isothermal conditions. The measurements were performed using cone/plate, plate/plate, and Couette geometries to assess the influence of the contact surface of the samples with air on their crosslinking behavior. The crosslinking process of the investigated polysilazanes in ambient atmosphere was found to occur faster than that in inert atmosphere. DSC and FTIR-spectroscopic investigations indicate that hydrolysis and polycondensation processes occur in both polysilazanes when crosslinked in air.Interestingly, the effect of moisture was found to be more pronounced in the case of the urea derivative. The evolution of the measured complex viscosity and dynamic moduli supported this finding. Furthermore, the variation of the time derivative of complex viscosity (dg*/dt) emphasizes structural changes during crosslinking of the samples which were ascribed to their contact with the ambient atmosphere. This study emphasizes the high potential of rheometry in investigating the crosslinking behavior of polymers in inert and ambient atmosphere.

Polysilazane‐Based Coatings with Anti‐Adherent Properties for Easy Release of Plastics and Composites from Metal Molds

“…The crosslinking behavior of the silazanes PHPS and HTTS has been discussed thoroughly in other studies. [ 3,6,10,37,38 ] However, since this behavior is fundamental to understand the influence of temperature on the anti‐adherent properties of the coatings, a discussion on this topic is presented herein.…”

“…In contrast to the methyl groups, vinyl side groups contribute to crosslinking by vinyl polymerization. However, because the onset temperature of these reactions is high, [ 38 ] evaporation of molecules with low molecular weight occurs before vinyl polymerization starts, evidenced by mass loss at low temperatures. The addition of the initiator DCP reduces this onset temperature, resulting in a faster crosslinking and a reduced mass loss.…”

Cure kinetics of a polysilazane system: Experimental characterization and numerical modelling

“…(11), where G 0 is the elastic shear modulus (or storage modulus), and G 00 is the viscous shear modulus (or loss modulus). The cross-point of G 0 and G 00 , which is the most commonly used gel point criterion [44,45], was found to occur very early (for polymerization degree lower than 1%) and did not allow a convincing criterion common to all experiment to be identified. This can be observed in Fig.…”

Tape casting of preceramic polymers toward advanced ceramics: A review

“…For the PDC route, specific rheological investigations are limited to a few PCP systems . Even less frequent are rheological studies with direct correlations to common shaping processes, such as extrusion or melt spinning .…”

“…109 For the PDC route, specific rheological investigations are limited to a few PCP systems. 56,[110][111][112][113] Even less frequent are rheological studies with direct correlations to common shaping processes, such as extrusion or melt spinning. 114 To the best of our knowledge, no specific investigation on mechanical properties of cross-linked PCPs before pyrolysis was performed so far.…”