Polyacenic polymers

The potential applications for conducting polymers are enormous and this has stimulated a large amount of research into this area. Not surprisingly, solid-state NMR spectroscopy has been applied to study these amorphous, insoluble and in many cases crosslinked materials [24]. Looking at the CP/MAS spectra of a series conducing polyacenic polymers, some of which were doped with iodine, it was possible to see the effect of the halogen upon conductivity. These resins were prepared by a conventional procedure for the preparation a Novolak-type phenol-formaldehyde resin. After synthesis, the phenol-formaldehyde resin were dissolved and solutions were cast as a film and heat treated to between 590-670°C in a N2 atmosphere to form the polyacenic film. The electrical conductivity of the films was shown to increase... 

The structure of polyacenic polymers, one of the typical conducting polymers, has been studied by infrared (IR), X-ray diffraction and ESR [17, 18]. From these studies, it was found that polyacenic polymers obtained by heating resins are amorphous and their structures are very complicated. Therefore, their exact structures have not been clarified because of their amorphous nature and insolubility. Kurosu et al. [19] studied the relationship between the structure and electrical conductivity of polyacenic polymer samples by high resolution solid-state NMR spectroscopy. 

The polyacenic polymer films are obtained by heating phenol-formaldehyde resin (PFR) at 590, 640 and 670°C, abbreviated as PAc590, PAc640 and PAc670, respectively. 

Table 16.5. Electrical conductivity and elemental analysis data of polyacenic polymers and phenol-formaldehyde resin...

Fig. 16.9. Structures of (A) phenol-formaldehyde resin and (B) polyacenic polymers.

The structures of PFR and polyacenic polymers are shown in Fig. 16.9. Figure 16.10 shows the relationship between electrical conductivity and heat-treatment temperature. This shows that the electrical conductivity of polyacenic polymer is increased as the heat-treatment temperature is increased and there is a linear relationship between electrical conductivity and heat-treatment temperature. Therefore, an increase in electrical conductivity is caused by the growth of the polyacenic structure. Furthermore, the electrical... 

Figure 16.11 shows CP/MAS spectra of PFR and PAc samples. The peak assignment of PFR was performed straightforwardly from reference data by Yamabe et al. [20] as shown in Fig. 16.11, where the numbers on the peaks correspond to the carbons of PFR as shown in Fig. 16.9. As seen from these spectra, the main peak (at 127-130 ppm) moves to low frequency and the peaks are broadened as the heat-treatment temperature is increased. Therefore, it can be considered that this spectral change originates from the structural change in going from PFR to polyacenic polymers by heat-treatment, as shown in Fig. 16.9(B). The intensities of the peaks at about 150 ppm, which are assigned to PFR carbons bonded to the hydroxyl group (carbon...

Fig. 16.11. Observed C CP/MAS NMR spectra of (a) phenol-formaldehyde resin (PER) (b) polyacenic polymer heat-treated at 590°C (PAc590) (c) polyacenic polymer heat-treated at 640°C (PAc640) and (d) polyacenic polymer heat-treated at 670°C (PAc670). Asterisks indicate spinning sidebands.

Fig. 16.12. Observed and simulated NMR spectra of polyacenic polymer heat-treated at...

Table 16.6. Observed C chemical shifts, halfwidths and relative intensities of polyacenic polymer samples...

Fig. 16.14. Plots of relative peak intensities against electrical conductivity of polyacenic polymers.

The e. s. r. and conductivity of polymers such as the polyacene/qui-none radical polymers (PAQR polymers), polyacetylenes and polybenzimidazoles have been investigated (59, 60, 61). The term eka conjugated has been coined to decribe their properties which are very similar to those previously described. The e. s. r. signal is without structure, the activation energy which ranges from 0.2—2.0 ev is considerably... 

Redox polymer film (pseudocapacitance) Polypyrrole, polythiophene, polyacene... 

A third example of this effect is evidenced by a study of the valence band structures of the series of n-phenyl molecules converging to the polymer p-polyphenyl whose valence band spectrum can be seen in Figure 6 ( ). This experience confirms the results obtained for the alkanes and the polyacenes. 

The condensation of aromatic acid anhydrides, e.g., phthalic anhydride, with aromatic hydrocarbons, e.g., napthalene, in the presence of ZnCl2 led to black polymer semiconductors of the polyacene quinone radical type [444, 445]. Resistivities in the order of 10 -10 °f2 cm were measured. High spin densities are characteristic [446]. An evaluation as active materials has not yet been performed. 

Peridi- or tetrachalcogen-bridged polyacenes have been claimed in the patent Uterature for the preparation of electrical conducting materials <88EUP285564, 93EUP521826>. They have also been claimed as copolymers for the preparation of radiation sensitive polymers <90EUP362143>. 

Polymers belonging to this group lie in the area between (CH)X and graphite. For example, the H/C molar ratios of (CH)X and graphite are unity and zero, respectively, whereas polyacene, being a laddered polymer of two trans- CR)x chains, has the H/C ratio 0.5. Some of the members of this group are illustrated in Fig. 15. 

Experimental attempts to synthesize any of the polymers described above have not been successful except a preliminary preparation of poly-perylene (Murakami and Yoshimura, 1984). Alternative efforts are currently being made to obtain polyacenic material through pyrolysis of various organic polymers such as phenol-formaldehyde resin (Yamabe et al., 1983 Tanaka et al., 1984b), polyacrylonitrile (Teoh et al., 1982, 1983), and poly(p-phenylene-1,3,4-oxadiazole) (Murakami et al., 1983). The group of these pyrolytic polymers behaves rather like amorphous semiconductors and is considered to be composed of fragments of polyacene to graphite, that is, a sort of coke, coal, and so on. 

Strictly speaking, polyacene is the fused-ring system having the structure shown in Figure 1.61b it is the most basic representative of ladder polymers. The... 

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