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Effect of ambient atmosphere on crosslinking of polysilazanes



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 (dη*/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. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

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