Self-assembled multilayers and photoluminescence properties of a new water-soluble poly(para-phenylene) Page: 3 of 8
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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-disulfonic-
dicarboxylic acid (Figure 1(b)) through sulfonation of poly(p-quaterphenylene-2,2'-dicarboxylic
acid). The sulfonated PPPso3 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.
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(p-
quarterphenylene-2,2'-dicarboxylic acid) was slowly added into an aqueous solution containing
23% SO3/H2SO4 (the ratio of polymer/SO3 is 1:2.3) at 0 C 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
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-quaterphenylene-
2,2'-dicarboxylic acid) used for sulfonation reaction, was obtained using the procedures reported
by Novak et al.. The purified product was characterized by 200 MHz 'H NMR(D20) (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 Fluorolog
The negatively charged PPPso3 polymer was assembled with a positive charged polymer
poly(diallyl dimethyl ammonium chloride) or PDDA to form multilayers. The self-assembled
multilayer of PDDA/PPPso3 films and spin casted films were formed on various substrates; these
include conductive RuO2 and ITO, semiconducting Si wafer, and nonconductive quartz or glass
substrates. The conductivity measurements were performed on a 100 PDDA/PPP bilayer film self-
assembled on RuO2 substrate. Self-assembled multilayer PDDA/PPP films on quartz and glass
substrates were also characterized by UV-Visible absorption and photoluminescence
measurements. Self-assembled PDDA/PPP multilayer films on Si(100) substrates were used for
the X-ray reflectivity study which was carried out with an 18-kW rotating anode X-ray generator
with a copper target and a four-circle diffractometer.
RESULTS AND DISCUSSION
The new sulfonated poly(para-phenylene) PPPso3 exhibits a high solubility in water at a
wide range of pH including acidic, neutral, or basic conditions. It can be easily dissolved in water
at pH values ranged from 1 to 14. This high solubility can be attributed to the increased numbers
of negative charges on the repeating unit (possibly four negative charges on each repeating unit) of
the sulfonated and carboxylated poly(para-phenylene) polymer. This highly water-soluble
polymer was characterized by a number of techniques to confirm its composition and rod-like
structure. ' H NMR spectrum(D20) showed broad resonances ranged from 6.6 to 8.2 PPM, which
can be attributed to the polymeric effect. The resolved vibronic features in the IR spectrum (KBr
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Shi, X.; Li, D.Q.; Luett, M.; Fitzsimmons, M.R. & Van Patten, G.P. Self-assembled multilayers and photoluminescence properties of a new water-soluble poly(para-phenylene), report, March 1, 1998; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc706283/m1/3/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.