Elucidating the degree of selectivity for NLO surrogate attachment to model compounds and a co-polyimide using the Mitsunobu reaction

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Title: Elucidating the degree of selectivity for NLO surrogate attachment to model compounds and a co-polyimide using the Mitsunobu reaction
Author: Woods, Timothy E.
Abstract: The goals of this research are: to elucidate the degree of selectivity shown using the Mitsunobu reaction for pendent attachment to phenol and carboxylic acid functional groups, and to make progress towards the synthesis of a novel, UV-Crosslinkable, Mellitic Acid Dianhydride (MADA)-containing, low color, nonlinear optical (NLO) pendent co-polyimide (co-PI). Two of the three co-PI components lower the hydrophilicity and color of the product polymer by incorporating C-F bonds between their aromatic rings: the diamine, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (Bis-AP-AF), and the dianhydride, 4,4’-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). MADA was synthesized using a previously established procedure, and its purity was verified by a 5.9% weight loss seen with thermogravimetric analysis (TGA). A novel organic compound containing MADA, N,N’-bis(2-hydroxyphenyl)-2,3,5,6-hexacarboxylic acid diimide [(2-AP)2MADA diimide], was synthesized to aid in selectivity determination. Two model compound systems are presented in order to elucidate the degree of functional group selectivity. Using 3,5-dihydroxybenzoic acid, a stoichiometric amount of a pendant was attached exclusively at a carboxylic acid in the presence of two phenol functional groups under ambient conditions in freshly dried NMP. This conclusion was supported by the disappearance of the broad carboxylic acid proton signal, complete retention of both phenol proton signals, and the appearance of pendent group peaks in the 1H NMR, and the appearance of a new spot in the thin layer chromatogram (TLC). Subsequent one-pot pendent attachment at the phenol groups was then shown, although an excess of fresh Mitsunobu reagents were required to achieve a modest yield. The (2-AP)2MADA diimide model compound was then synthesized in freshly dried NMP using a one-pot approach without the presence of a catalyst. Structural verification was provided by 1H NMR, FTIR, and MS. Based on the presence of the carboxylic acid protons at ~ 8.20 ppm in the 1H NMR and the presence of a weak, broad stretch at 3060 cm-1 xvi in the FTIR, the presence of a strongly H-bonded or zwitterionic structure was indicated. Exclusive pendent attachment at the phenol groups of (2-AP)2 MADA Diimide using a stoichiometric amount of Mitsunobu regents was verified by the disappearance of the phenol proton peak at ~10.0 ppm in the 1H NMR and 3323 and 1095 cm-1 peaks in the FTIR, and the concurrent appearance of several peaks corresponding to ether linkages at 1244 and 1118 cm-1 in the FTIR. One-pot attachment of a second pendant at the unreacted functional group was then shown. A large excess of Mitsunobu reagents was required however to achieve a modest yield. Finally, the co-PI[Bis-AP-AF/6FDA)0.9(Bis-AP-AF/MADA)0.1]n was synthesized using a one step imidization approach in freshly dried NMP. A high degree of imidization was achieved, demonstrated by the weak peak at 1653 cm-1 in the FTIR. Structural confirmation was provided by 1-D 1H and 2-D COSY NMR and FTIR. TGA of the product polyimide showed initial major decomposition at 396 °C. Pendent attachment was carried out in a similar fashion to that used for (2-AP)2MADA diimide, and most likely takes place exclusively at the phenol groups on either mer, as indicated by a peak at 1139 cm-1 corresponding to ether linkages in the FTIR. Additional structural confirmation was provided by 1H NMR and FTIR. A subsequent one-pot pendent attachment at the unreacted functional groups was also shown to be possible by 1H NMR and FTIR. Only a modest yield was obtained however due to the use of a stoichiometric amount of Mitsunobu reagents.
Record URI: http://hdl.handle.net/1850/7725
Date: 2008-09

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