Synthesis of Conjugated Polymers by Vapor Deposition Polymerization
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ructural derivatives of poly(phenylene vinylene)s and poly(2,5-thienylene vinylene)s have been prepared by the soluble precursor route and used for the preparation of light emitting diodes (LEDs).7'8 Vapor deposition polymerization was first reported by Gorham in 1996.9 A strained [2,2]paracyclophane was converted by vacuum pyrolysis at 600 °C to form a reactive intermediate p-xylene, stable in the vapor phase, which spontaneously polymerized upon condensation to form a poly(p-xylene) film. This was a very useful method to obtain a polymer film free from contaminant because of using no solvent. This methodology was used recently by Staring et al.'° and Shafer et al." to generate PPV films by vapor phase pyrolysis of a, a '-dihalogenated p-xylenes.
Recently we reported the synthesis of poly(2,5-thienyleneethylene) and poly(2,5-furyleneethylene) by vapor phase pyrolysis of (5-methyl-2-thienyl)methyl benzoate and (5-methyl-2-furyl)methyl benzoate.12 In this study, the synthesis of poly(2,5-thienylene vinylene) and poly(4,7-thianaphthene) by vapor phase pyrolysis of 2,5-di(bromomethyl)thiophene and 2,3-diethynylthiophene is presented. The chemical structures and thermal properties of the obtained polymers are characterized by IR, NMR, differential scanning calorimetry and Xray diffraction. EXPERIMENT Materials 2,5-Di(bromomethyl) thiophene (1M) was prepared by a procedure reported in bis(triphenylposphine)palladium 2,3-Dibromothiophene, the literatures.13"14 chloride, 2-methyl-3-butyn-2-ol and all other reagents were obtained from Aldrich and used as received. Techniques 'H and 13C NMR spectra (300 MHz) were recorded on a Varian VXR-300 spectrometer and infrared spectra were measured with a Nicolet 520 FT-IR spectrometer. Elemental analysis was determined using a Heraeus elementary analyzer. Thermal transitions and thermodynamic parameters were determined by using a Seiko SSC/5200 differential scanning calorimeter equipped with a liquid Heating and cooling rates were 10 'C /min. nitrogen cooling accessory. Thermogravimetric analysis was performed on a Seiko TG/DTA 200 thermal
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analyzer at 10 C /min. The thermal decomposition temperature (Td) was read at a temperature at which 5% weight loss occurred. Gel permeation chromatography (GPC) was run on an Applied Biosystems 400 LC instrument equipped with a differential refractometer, a UV detector, and a set of PL gel columns of 102, 5 x 102, 10', and 104 A. The molecular weight calibration curve was obtained by using standard polystyrenes. X-ray diffraction measurements were taken with nickel-filtered Cu K a radiation with a Rigaku powder diffractometer. Synthesis of monomers and polymers Schemes 1 and 2 outline the synthetic routes used for the preparation of monomer 2M and poly(2,5-thienylene vinylene) and poly(4,7-thianaphthane)
/\650 S
BrH 2C
+S
CH 2Br
0C
lX10-3 torr
H2 C~ S
Z'
CHBr
S
ý
n
Scheme 1. Synthesis of poly(2,5-thienylene vinylene) by vapor deposition ploymerization.
Br S'\
1) HCEC-C(CH3)2OH, Pd(PPh 3)2Ci2 , CuI, PPh 3 , Et3N
-CH
3000 C 1
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