Beschreibung:
<jats:title>Abstract</jats:title><jats:p>The dielectric behavior of different polar high polymers at ultra‐high frequencies has been investigated by means of a dielectrometer, suitably modified to permit measurements at different temperatures. Experimental measurements were made at about 9 × 10<jats:sup>9</jats:sup> cps over the temperature range of −150 to 200°C. for polyoxymethylene, polythiomethylene, poly(3,3′‐chloromethyl)oxetane (Penton), polycarbonate of 4,4′‐dioxydiphenyl‐2,2′‐propane (Makrolon), poly(vinyl alcohol), poly(vinyl acetate), poly(vinyl chloride), vinyl chloride–vinyl acetate copolymer, and two ABS plastics, type B (blend) and type G (graft). On comparing the dielectric behavior of the examined materials at ultra‐high frequencies with the corresponding ones determined at low or at radiofrequencies, it is observed that, in the microwave region, all relaxation peaks, either connected with cooperative motions in main chain (primary processes) or with local motions in the backbone or in side chains (secondary processes), usually observed at lower frequencies, tend to disappear; the corresponding relaxation effects, however, manifest themselves through a progressive increase of losses with increasing temperature, which is particularly marked above the glass transition temperature <jats:italic>T</jats:italic><jats:sub><jats:italic>g</jats:italic></jats:sub>. The latter transition, in spite of the very high frequency, is easily distinguished, in most cases, by the sudden change of slope in the tan δ versus temperature curve which accompanies its onset. This is explained on the basis of the very wide distribution times of molecular relaxation processes in polymers and the increase in strength of the secondary relaxation effects, which is verified at <jats:italic>T</jats:italic><jats:sub><jats:italic>g</jats:italic></jats:sub>, as a consequence of the increased kinetic energy of macromolecules and of the larger free volume for orientation of side chains. Each case is discussed separately and the experimental results interpreted on the basis of the molecular structure and chain mobility of the examined polymers.</jats:p>