Self-Assembled Multilayers and Photoluminescence Properties of a New Water-Soluble Poly(Para-Phenylene)
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-(-c~ P_64-f t COOH(M) Figure 1(a). Poly(p-quarterphenylene2,2'-dicarboxylic acid
SO 3H(M)
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SO3H(M)
OOH(M)
'-
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n
COOH(M)
Figure 1(b). Poly(p-quarterphenylenedisulfonic-dicarboxylic acid
133 Mat. Res. Soc. Symp. Proc. Vol. 488 ©1998 Materials Research Society
The mixture of dimethylformamide/aqueous solvent(25/75) was needed in order to prepare concentrated polymer solution for processing (>5% w/v). Thus, there is a need to prepare highly water-soluble, rigid-rod conducting polymers which can be processed entirely under environmentally benign conditions. Another important consideration is that the charged groups on the repeating unit of the polymer backbone can serve as anchor points in self-assembled thin film growth or LED's fabrications. It is anticipated that the increase in the number of charges on each monomeric unit of the polymer will provide stronger cation-anion attractions in the self-assembly process. In this paper, we report a new PPP polymer-poly(p-quaterphenylene-disulfonicdicarboxylic acid (Figure l(b)) through sulfonation of poly(p-quaterphenylene-2,2'-dicarboxylic acid). The sulfonated PPPso 3 has enhanced solubility in aqueous solution and photoluminescent properties in both solution and solid state films. Self-assembled multilayer films of this new PPP are prepared and the structure of the films is characterized with X-ray reflectivity measurements. EXPERIMENT The modified PPP bearing both sulfonate and carboxylate functional groups was prepared by the following route. In a typical experiment, the golden color powder of poly(pquarterphenylene-2,2'-dicarboxylic acid) was slowly added into an aqueous solution containing 23% SO3/H 2SO4 (the ratio of polymer/SO 3 is 1:2.3) at 0C degree under vigorous stirring. Upon the completion of the addition, the reaction solution was stirred at 0°C degree for an hour, and then was heated at 70'C for 7 hours. The product mixture was cooled down to room temperature and was neutralized by adding dilute KOH solution. The solvent in the mixture was removed under vacuum condition. The dried crude product was purified on a column packed with Florisil. Methanol was selected as eluent to collect the product. Final product was collected as yellow color powder. Monosulfonated triphenylphosphine and its palladium catalyst, which are needed in the cross coupling polymerization, were synthesized according to the literature[7-8], while the monomers of 4,4'-dibromicdiphenic acid and bis(boronic acid) diphenyl were also synthesized and characterized by the reported methods[9-10]. The precursor polymer, poly(p-quaterphenylene2,2'-dicarboxylic acid) used for sulfonation reaction, was obtained using the procedures reported by Novak et al.[6]. The purified product was characterized by 200 MHz 'H NMR(D 20) (Gemini NMR spectrometer) and IR (KBr pellet) (Bio-Rad-40). Absorption spectra were recorded using a Perkin-Elmer Lambda-19 UV/VIS/NIR spectrometer. Photoluminescence(PL) measurements on (un)sulfonated PPP solutions and self-assembled films were obtained using a SPEX
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