Preparation of polymeric materials with semiconductor properties

Abstract

Organic substances described in the literature as having semiconductor properties usually involve the presence of condensed aromatic rings and atoms of nitrogen.' The polymers with conjugated double bonds are therefore of considerable interest, especially those, containing in the chain, atoms which have electrons in the outer levels that do not participate in the chemical bond (for example, atoms of nitrogen). In such polymers, current carriers should appear quite easily, and with a sufficiently high regularity of the polymeric structure, the electron dispersion should be small. The required degree of regularity can be roughly estimated on the basis of the quantity of free run of the electrons in a semiconductor, the lengths of the C-C bonds, the lengths of the monomeric links, and the lengths of the electron wave. Tentative computations show that, in the case of a maximally drawn filament in which the polymer molecules are oriented in the direction of the current, in order to avoid dispersion on the structural irregularities as caused by irregularities in the configuration, it is sufficient if in the main chain of the polymeric molecule, for every 30-35 monomeric units, the branches present consist of no more than 12-15 atoms of carbon.The creation of polymers of such a degree of regularity is a t the present time quite feasible.A series of previous s t u d i e P 4 was dedicated to obtaining polymers having conjugated double bonds, chelate polymers, and those polymers, in addition, which contain heteroatoms in the basic chain.With such a point of view, interest was expressed in the condensation products of phthalic anhydride with hydroquinone and N-phenylenediamine having approximately the structure : *Presented a t the

Mass DSC/TG and IR ascertained structure and color change of polyacrylonitrile fibers in air/nitrogen during thermal stabilization

“…It has been reported1, 2 to undergo chemical reactions in stages on thermal treatment. The following chemical reactions are believed to take place: (1) cyclization of nitrile groups leading to hydronaphthiridine rings (cyclization)3–5; (2) oxidation of hydrogenation leading to a certain degree of aromatization (dehydrogenation)6; and (3) oxidation of hydronaphthiridine rings leading mainly to acridone and some other structure (oxidative reaction) 7. During stabilization, the bulk of the chemical changes are accompanied by release of exothermic energy and are able to thermochemical analysis 8, 9.…”

Progress in the chemistry of polyconjugated systems

“…Generation of methyleneimino groups, resulting from migration of the tertiary hydrogen atom, is the initiating stage of the process. This is demonstrated by the absorption band at 3200-3400 c m -t , corresponding to stretching vibrations of the hydrogen in the C = N -H group [233][234][235][236][237]. Electronic spectra also reveal new absorption bands 234) Conformational transformations in the polymeric chains with increased rigidity of the chains are indicated by viscosity characteristics of solutions and by the temperature dependence of the square of the second moment (H 2) in the NMR spectra of the polymers 4°' 231, 2o9) These data are presented in Fig.…”

Semiconducting and Conducting Organic Pyropolymers

“…Another system of considerable interest is polyacrylonitrile. When this 'polymer is pyrolyzed in the temperature range of 400°to 700°C ., the resistivities of the pyrolyzed material approach those of semiconductors (13,24). The electrical conductivity of polyacrylonitrile may be increased by pyrolysis in an ammonia atmosphere.…”

“…This is indicated by a decrease in the infrared C=N absorption band and the appearance of the C-N band, as well as changes in the mechanical properties of the material. Structural changes during the pyrolysis of polyacrylonitrile are believed to be due to the following condensation: Geiderikh and colleagues (13) reported activation energies of conduction of pyrolyzed polyacrylonitrile between 0.32 and 0.65 e.v. and thermoelectric powers of +72 to +108 pvolts/0 C. with samples pyrolyzed between 400°to 500°C.…”