Thermal and optical properties of novel polyurea/silica organic-inorganic hybrid materials

Current optical polymeric materials for advanced fiber laser development are susceptible to degradation due to the heat generated in high power usage. A suitable replacement light stripping material was explored to overcome this problem by examining optical and physical properties such as transmission/absorption, refractive index, thermal conductivity, and thermal stability. The synthesis and characterization of two new polyurea/silica ORMOSILs (ORganically MOdified SILicates) suitable for high temperature (up to 300 A degrees C) optical applications are reported herein. A one-pot, room temperature synthesis is based upon commercially available bis-isocyanates and an amino-silane. These materials exhibit the combined traits of both glass and polymer by displaying optical clarity over a wide range of wavelengths stretching from the edge of the UV (250 nm) to well into the NIR (2,000 nm), refractive indices in the visible spectrum (n = 1.50-1.63), thermal conductivities of 0.26 +/- A 0.09 W/mK (ORMOSIL-A) and 0.27 +/- A 0.07 W/mK (ORMOSIL-B), and thermal stabilities up to 300 A degrees C. The hybrid materials were found to be easily processed into films but thick casts (> 2 mm) were subject to increased rates of cracking and longer curing times. Although this is typical of sol-gel chemistries, the organic constituents of ORMOSILs reduce this effect as compared to purely inorganic sol-gels. The effect of thermal aging on the materials' properties will also be presented as well as a comparison of these materials and the current state of the art light stripping material.