ABSTRACT:We have successfully incorporated Diels-Alder reversible chemistry into epoxy resins. The Diels-Alder chemistry goes in the forward direction at 60°C and reverses at or above 90°C. One resin was formulated with other commercial ingredients into foamed epoxy. The foam, shown to have mechanical properties similar to foams formed with conventional epoxy resins, is being utilized for electronic encapsulation. Because of the built-in reversible chemistry, the foams can be easily removed by dissolution in 1-butanol at 90°C. Removal allows for the rework, upgrading, or dismantlement of the electronic components.

We report the first sol−gel polymerization of alkoxysilane monomers in supercritical carbon dioxide (SCCD) as the polymerization solvent. Monolithic silica and silsesquioxane gels were formed in SCCD by the nonaqueous polymerization of tetramethoxysilane and 1,4-bis(triethoxysilyl)benzene, respectively, with formic acid (99%). The gels were dried to give high surface area, mesoporous aerogels by simply venting carbon dioxide from the autoclave.

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With the eventual phase-out of chlorofluorocarbons, and restrictive regulations concerning the use of cleaning solvents such as hydrochlorofluorocarbons, and other volatile organic compounds, it is essential to seek new, environmentally acceptable cleaning processes. In the DOE Complex and in industry, an environmentally sound process for precision cleaning of machined metal parts is one of the issues that needs to be addressed. At Sandia, we are investigating the use of supercritical carbon dioxide (CO2) as an alternative cleaning solvent for this application. Carbon dioxide is nontoxic, recyclable, and relatively inexpensive. Supercritical CO2 has been demonstrated as a solvent for many nonpolar organic Compounds, including hydrocarbon-based machining and lubricating oils. The focus of this work is to investigate any corrosive effects of supercritical CO2 cleaning on metals. Sample coupons of several common metals were statically exposed to pure supercritical CO2, water saturated supercritical CO2, and 10 wt% methanol/CO2 cosolvent at 24,138 kPa (3500 psi) and 323°K (50°C) for 24 hours. Gravimetric analysis and magnified visual inspection of the coupons were performed before and after the exposure tests. Electron microprobe, x-ray photoelectron spectroscopy (XPS), and Auger electron surface analyses were done as needed where visual and gravimetric changes in the samples were evident. The results of these experiments will be reported. DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

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