Larbi B, Hachemaoui A, Ahmed Y, Abdelghani B, Karime C, Mohamed B. Synthesis of poly[(pyrrole-2,5-diyl)-co-(4-hydroxylbenzylidene)] catalysed by Maghnite– H+. Orient J Chem 2013;29(4)
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Larbi B, Hachemaoui A, Ahmed Y, Abdelghani B, Karime C, Mohamed B. Synthesis of poly[(pyrrole-2,5-diyl)-co-(4-hydroxylbenzylidene)] catalysed by Maghnite– H+. Orient J Chem 2013;29(4). Available from: http://www.orientjchem.org/?p=1146
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Most of the PPHB were found to be soluble in organic solvents such as tetrahydrofuran (THF), CH2C12, N,N-dimethylformamide (DMF), and sulfolane. Although polymers have highly conjugated chains due to the high degree of dehydrogenation, they were very soluble in organic solvents such as THF, giving grey solutions of high concentrations. The very good solubility of polymers in spite of their high degree of π-conjugation is due largely to the bulky side groups (Φ) at the methane carbon =C (Φ) link and also to the low molecular weight to some extent.
The UV-Vis absorption was recorded with an OPTIZEN 2120 spectrometer. Figure 2 shows the optical absorption spectra of polymers PPHB in CH2Cl2 solution. The colours of the polymer solution were brown or almost black. The absorption spectra in Figure 2 shows the band in the range of (300–350) nm assigned to the π-π* transition of the aromatic heterocycles since it corresponds to the same band as its precursor, and the band in the range of (400–430) nm is assigned to the π-π* transition.
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Figure 2: Spectre UV-visible de PPHB (in CH2Cl2).
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The 1H-NMR spectra of PPHB were obtained to further investigate and confirm the proposed structure. Figure 3 shows the 1H-NMR spectrum of PPHB in DMSO, The resonance at 10.45 ppm is assigned to the proton resonance of hydroxyl group in the benzene ring. The resonance at 9.14 ppm is assigned to the proton resonance of hydrogen in pyrrole .we observe a new proton resonance of 6.64–6.93 ppm was observed, indicating the formation of the quinoid rings in the polymer backbone, x and y are impurities. The polymers so obtained are readily soluble in common organic solvents, such as chloroform, dichloromethane, THF.
 | Figure 3. 1H-NMR spectrum (300 MHz) of PPHB in DMSO Click here to View figure |
Figure 4 shows the FT-IR absorption spectra of PPHB. A distinct peak at 772 cm_1 of PPHB is due to the Cb–H the out-of plan vibration, characteristic of α-linkage in pyrrole ring. The peak at 1685 cm-1 of Fig. 4 is assigned to the C=C and the stretching vibration of aromatic in phenylene , this assignments is based on the FT-IR spectrum of pyrrole. The broad band at 3303 cm_1 is N–H stretching vibration of pyrrole ring and O–H vibration of hydroxyl on benzene ring in the side chain.
 | Figure 4.FT-IR spectrum of PPHB Click here to View figure |
Figures 5 show the TGA curves of PPHB obtained in a helium atmosphere at a heating rate of 100 0C/min. This polymer show bad thermal stability. For example, the intrinsic PPHB has an onset of thermal decomposition of 100 0 C attributed to OH, the second at 114 0C is assigned to carbon bridge, so the PPHB is little stable at high temperature.
 | Figure 5. TGA spectra of PPHB Click here to View figure |
Conclusions
Maghnite–H+, proton exchanged montmorillonite clay is an effective initiator for the copolymerization of 4-hydroxybenzaldehyde with pyrrole.
A novel polymer, poly[(pyrrole-2,5-diyl)-co-(4-hydroxybenzylidene)], which has a π-conjugated chain was synthesized by using Maghnite–H+ as catalyse. The resultant polymer showed good solubility in common organic solvents and good film formability. Such results may serve primarily to illustrate a new strategy to increase the solubility of low band gap polymers through the arrangement of different aromatic heterocycles in conjugated polymer backbones.
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