Poly-p-xylyliden. Synthesen und beziehungen zwischen struktur und elektrophysikalischen eigenschaften

Foly-p-xylylidene has been synthesized by bifunctional carbonyl olefination of terephthalaldehyde according to WITTIG'S reaction and by means of p-xylylene-bis-(diethyl phosphonate) as well as by dehydrochlorination of p-xylylene dichloride with sodium hydride in dimethyl formamide and with potassium amide in liquid ammonia. Then followed a comparative investigation of the products obtained. Methyl- and methoxy-substituted poly-p-xylylidenes II and III are obtained from 2.5-bis-(chloromethyl)-p-xylene and -hydroquinone dimethyl ether. I–III are being analyzed by IR and reflection spectra as well as by thermogravimetry. The poly-p-xylylidenes I–III possess semiconducting properties and photoconductivity, typical values for the dark conductivity and activation energy of I being σ₄₀₀°K ～ 10^?15 ohm^?1 cm^?1 and E_D = 2,4 eV. Absorption spectra and photoconductivity spectra occur in the same spectral region, photoconductivity on the long-wave edge of absorption possessing a maximum. The excitation energy for the photoconduction of I, E₀ = 2,35 eV, is of the same value as E_D and is approximately in accordance with the theoretically calculated value for the π–π* transition of the isolated macromolecule. Corresponding relations result from the substituted polyxylylidenes II and III. In order to characterize the conducting phenomena more closely measurements are being made concerning the dependence of the photocurrent and its relaxation time from voltage, temperature and radiation intensity. Also, the photoconductivity with combined optical excitation as well as the influence of oxygen on photoconduction are being examined.