Rikio Yokota

Melting Behavior of Some Oligomers of Heterocyclic Polymers by Differential Scanning Calorimetry

The softening point of polybenzimidazole involving aromatic ether linkage in the main chain is not measurable below degradation of the polymer. The various oligobenzimidazoles and benzothiazole and benzoxazole derivatives with analogous structures were synthesized and their melting point Tm and heat of fusion ΔH were measured by differential scanning calorimetry. The entropy of fusion ΔS was calculated by ΔS = ΔH/Tm. The accuracy of the method was examined and the effect of imidazole ring on the melting behavior was investigated.

Dynamic Mechanical Properties of Aromatic Polyamideimide Degraded in NO2 Atmosphere

The degradation of aliphatic polyamide as nylon 66 in an NO2 atmosphere has been investigated by Jellinek,1 based on the mole-cular weight changes determined by the change of solution viscosity. The aromatic polyamideimides are also accessible to NO2, but are slightly soluble in polar solvents as N-methyl pyrrolidone(NMP) and the solutions obtained are not readily stable to estimate the degree of degradation from the usual viscosity measurements. Therefore, we investigated the degradation of aromatic polyamideimide by following the change of dynamic mechanical properties in an NO2 atmosphere.

Dynamic Thermomechanometry of Aromatic Polyamideimide

Temperature dependences of dynamic mechanical properties of commercial films of aromatic polyamideimide(PAI) were measured at uniform heating rates “by using modes of torsional, tensile, and flexural oscillations. Torsional oscillations of the film were measured with a home-made inverted torsional pendulum, tensile oscillations with a Rheovibron DDC IIC, and flexural oscillations with a du Pont 980 Dynamic Mechanical Analyzer. Corresponding molecular relaxations were found for each oscillation mode. Dynamic properties of composites of PAI reinforced with straight carbon fibers and with a glass cloth, and of PAI film sandwiched between two steel plates were measured for comparison. Similar results as obtained for film samples were found also for these composites. Degradation of PAI in an NO2 atmosphere could be followed by these techniques. A new molecular relaxation due to degraded surface layers was found below glass transition, and this relaxation was shifted to higher temperatures and shaded by glass transition after thermal treatments of degraded films.

Melting of some Aromatic and Heterocyclic Oligomers

The softening point of the aromatic or heterocyclic polymers is very high and usually undetected up to the decomposition point. The melting behavior of oligomers with the same basic structure of molecules as polymers has been measured by differential scanning calorimetry. The dependences of melting point, Tm and the enthalpy, Δntropy, Δlting on the degree of polymerization and the structure of molecules are discussed. The entropy of melting per ring for p-oligophenyl homologues decreases with the number of phenyl rings, n. For the longer p-phenyl chains, a sort of molecular arrangement would remain after melting; then, ΔS becomes low for the higher homologues, and Tm increases with n. A quite similar behavior was found for oligoacenes. On the other hand, Tm of m-oligophenyl homologues does not increase markedly with n. The asymmetric structure of the higher m-phenyls prevents the strong interactions between molecules in the crystalline state; therefore, AH becomes low for these molecules.