Preparation of network  -conjugated copolymers with Ullmann type

gotoh@ims.tsukuba.ac.jp ABSTRACT Ullmann type polycondensations in the presence of CuI and a base were carried out to afford network type  -conjugated copolymers. Infrared absorption spectroscopy measurements and surface observation using a scanning electron microscopy are carried out. Electron spin resonance spectroscopy measurements revealed that the cross-linked copolymers thus obtained contain small amount of copper. This polymerization conveniently allows production of network  -conjugated polymers. The polymer can be expected

Polymerization was conducted between dibromoarylene, such as dibromo-3,4-ethylenediioxythiophene (EDOTBr 2 ), 2,5-dibromothiophene, or 2,5-dibromopyridine), and p-phenylenediamine as shown in Scheme 1. A solution of the dibromoalyrene, dibromobenzene, and K 2 CO 3 in nitrobenzene was stirred for 24 h at 140 ºC. Then, the reaction mixture was poured into a large volume of methanol. After filtration, the product was washed with a large volume of distilled water, and a large volume of methanol again. Filtration followed by drying in vacuum yielded network copolymers. The copolymers thus obtained are abbreviated as Poly1 (poly(EDOT-aniline), Poly2 (pyridine-aniline), Poly3 (thiophene-aniline). The copolymers are infusible because of formation of polymer network by cross-link.

1. IR
IR absorption spectroscopy measurements were carried out with the KBr method ( Figure 1). Poly1 shows absorption bands at 1628 cm -1 (C=C stretching, quinonoid) [8], 1518 cm -1 (C=C stretching, benzenoid), and 1089 cm -1 (C-O-C, stretching, benzenoid). An absorption bands at around 3300 cm -1 due to N-H stretching was not observed. Wide range absorption from 4000-2000 cm -1 indicates that the polymer is doped state. Poly4 shows the same absorption bands as Poly3.  HBr yielded during the reaction functioned to be a dopant to the resultant polymer (K 2 CO 3 in the reaction may not neutralize it).

ESR
Electron spin resonance (ESR) measurements were carried out for the powder of the polymers [11]. Polymers show the ESR signals at around g = 2.08. Spin numbers of the polymers are to be in the range of 7-9 × 10 -6 spins/g. However, an ESR signal due to paramagnetic copper was overlapped on the polymers signal. This result indicates that removal of the trace amount of copper as a catalyst from the resultant polymer seems to be difficult.

4. UV-VIS
The polymers are slightly soluble in N-methyl pyrrolidone (NMP). The UV-VIS optical absorption spectra of the polymers are shown in Figure 4. These polymers display an absorption band at 540 nm except Poly2 (sh, 698 nm) due to-* transition of the main skeleton [12]. This result demonstrates that the network polymers are consisting of -conjugate system.

.CONCLUSIONS
Ullmann polycondensation reaction for formation of tertiary amine allows network copolymers consisting of arylene (EDOT, pyridine, and thiophene) and aniline units. The structures were confirmed using IR absorption spectroscopy measurements. Surface structure of the polymers was observed using a SEM. The -conjugated network polymers thus obtained may be useful for thermo-resistance materials, sensors, and antistatic organic materials.