Polyimides. Heteroatom and Heterocyclic Polymers

Photoconductivity of Kapton, (polypyromellitimide where R is oxygen) was investigated in detail [224-234]. Frenkel, Onsager, hopping and other models were used by different authors for explanation of the photoconductive properties. The photoconductivity spectra of Kapton film for various directions of the electric field are presented in Fig. 29 [230]. The high anisotropy depending on 

Compared to Kapton, more sensitive soluble polyimide films were investigated [235-236]. A photosensitivity of up to 30 m2 J 1 was achieved in electrophotographic regimes. The photogeneration of the charge carriers occured via exiplex formation and the holes are the predominant carriers. The spectral 

New types of polymers containing imide groups were proposed recently with high photosensitivity [237, 238] of the order less than lpj. Photosensitivity of the polymers composed of a series of thiophenylenes moieties and imide groups [238] remarkably increased with the increase of crystallinity. The overlapped rr-orbitals perpendicular to the polymer chains lead to the more extended conjugated system. 

Sensitized for blue-green or red light, photoconductive polyimides and liquid crystal mixtures of cyanobiphenyls and azoxybenzene have been used in spatial light modulators [255-261]. Modulation procedure was achieved by means of the electrically controlled birefringence, optical activity, cholesteric-nematic phase transition, dynamic scattering and light scattering in polymer-dispersed liquid crystals. 

The modulators mentioned above contained liquid crystal molecules. An entirely solid state device is naturally preferable in practice. The polymer-dispersed liquid crystal materials may be prospective counterparts of the modulator. One of the modes of operation of such thin films are as follows. The 

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