Synthesis and Purification of Tunable High Tg Electro-Optical Polymers by Ring Opening Metathesis Polymerization

Report No. ARL-TR-5651
Authors: Robert H. Lambeth, Joseph M. Dougherty, Joshua A. Orlicki, Adam M. Rawlett, Robert C. Hoffman, Timothy Pritchett, and Andrew G. Mott
Date/Pages: September 2011; 24 pages
Abstract: This report summarizes efforts to date toward preparing electro-optical polymer by ring opening metathesis polymerization. Initial work involved preparing model electro-optical polymers with tunable glass transitions. Random copolymerization of a norbornene ester tethered to E-O chromophore Disperse Red 1 (DR1) with various levels exo-N-Phenylnorbornene-5,6-dicarboxamide (NDI) and 5-carbomethoxy-2-norbornene produced materials with controlled Tgs. The Tg could be varied from 89 to 189 °C by modifying the feed ratio of the 3 monomers enabling materials to be produced according to desired processing conditions. The polymers were tested for electro-optical activity but displayed very little or no alignment along an electric field. The lack of activity is potentially the result of residual polymerization catalyst remaining in the final polymer product. To probe this further, a comprehensive investigation was performed to discover purification methods capable of reducing residual catalyst to acceptable levels. Initially, baseline levels were established for polymer purified via traditional methods involving multiple precipitations. The residual catalyst levels ranged from 240 to 140 ppm depending on the number precipitations. Several different strategies were employed to further reduce the trace metal remaining in the final polymer product. The first strategy involved the use of catalyst modifiers and various adsorbents. None of the methods explored reduced the catalyst level below 100 ppm while significantly reducing the yield of polymer due to adsorption of the polymer. The second strategy involved the use of heterogeneous functionalized particles to scavenge the catalyst from the solution. Filtration of the particles followed by precipitation produced polymers with 1060 ppm residual catalyst, depending on the type of particle used, surface functional groups, and number of equivalents. The third strategy used small organic molecules that could coordinate to the metal species and modify the solubility of the catalyst, facilitating partitioning of the catalyst into the precipitation solvent. Several types of molecules with varied functionality reduced the residual catalyst level to 30120 ppm, depending on the loading. Reducing the amount of trace catalyst significantly improved the oxidative stability of the polymer.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2011