AbstractThe evolution of hydrogen fluoride from a vinylidene fluoride/hexafluoro‐propene/tetrafluoroethylene elastomer has been studied over the temperature range 200–275 °C in air. The rate of evolution is affected by the diamine curing agent, the carbon black filler and the acid acceptor used and their effects are interrelated. The acid acceptor also influences the crosslink density attained in the curing process. It was found that some metallic hydroxides and carbonates, in whose presence an acceptable level of crosslinking was achieved, were some 50 to 100 times more efficient than the magnesium oxide normally used in reducing the rate of hydrogen fluoride evolution.

AbstractPolyimides were synthesised from a number of diamines and dianhydrides and their stability determined by thermogravimetric analysis at 400°C in air. Wherever possible high molecular weight films obtained by thermal condensation of the polyamic acid intermediates were studied. If this was not possible, films obtained from acetic acid anhydride ciclised polymers or thermally cured powders were used.A well defiend order of stability was observed for the polyimides prepared from pyromellitic dianhydride and a variety of diamines. The simplest and most symmetrical structures had the greatest thermal stability. Lowest stabilities were observed when linking groups were electronegative in nature.

AbstractEs werden eine Anzahl N,N′‐substituierter Imide der Pyromellitsäure hergestellt und deren Schmelzpunkt, Löslichkeit und IR‐Spektren aufgenommen.

AbstractPolyimide samples in the form of powders, films and sintered mouldings were prepared from pyromellitic dianhydride and 4,4′‐diaminodiphenyl ether. The effect of environmental variables on the oxidative stability at 400°C of the high molecular weight films was studied, and it was shown that hydrolytic processes could greatly accelerate the degradation. The higher stability of powders was attributed to the presence of low molecular weight fractions which could inhibit these hydrolytic processes. Improvement of the stability of the films by the addition of low molecular weight materials during the casting process and the destabilisation of powders by prolonged solvent extraction gave support to this hypothesis.For comparison of thermal stabilities of polypyromellitimides of differing chemical structure weight loss results should therefore be determined on high molecular weight films under controlled humidity conditions.

AbstractTreatment of a polypyromellitimide with hydrazine hydrate yields the biscyclohydrazide of pyromellitic dianhydride and the diamine originally used in the preparation. This reagent was, therefore, employed in a study of oxidised poly‐N,N′‐(4,4′‐diphenylether)pyromellitimide film in an attempt to elucidate the structural changes which had taken place. The most important process appeared to be cleavage of the aryl‐ether bond followed by reactions leading to the formation of polyaromatic aggregates. Breakdown of the imide ring structure also occurred.

AbstractThe amounts of unchanged pyromellitimide and diphenylether components in a poly‐N,N′‐(4,4′‐diphenyl‐ether)pyromellitimide film were determined as a function of the time of oxidation at 400°C. Coupling of the diphenylether portion of the chain to give complex aromatic structures occurred at a faster rate than destruction of the pyromellitimide ring. Both these processes were much faster than the overall rate of oxidation as measured by weight loss.

AbstractHigh molecular weight poly‐N,N′‐(4,4′‐diphenylether)pyromellitimide film was prepared from pyromellitic dianhydride and 4,4′‐diaminodiphenylether and the oxidative degradation at 400°C was studied by weight loss measurements, infrared spectrometry and saponification experiments. The results indicated the rapid development of crosslinks between the polyimide chains.

AbstractThe melting point, solubility and infrared spectra of a number of aromatic imides, mainly disubstituted N.N′‐diphenylpyromellitimides, have been determined. The variation in properties observed could be explained satisfactorily by making certain assumptions about the planarity, polarisation and intermolecular interactions of the compounds.

AbstractAromatic polyimides were prepared from pyromellitic dianhydride and a number of aromatic diamines. The effect of certain variables on the polymerization to, and the degradation of, the intermediate polypyromellitamic acids was studied, and a previously unrecorded reaction intermediate was isolated and identified. From these studies the conditions necessary to obtain high molecular weights were defined. Techniques were developed for the fabrication of satisfactory films and moldings.

AbstractThe thermal degradation in oxygen of fifteen polymers containing aromatic rings in the chain has been studied by a weight loss method. The relative thermal stabilities of the different polymers have been determined and, where possible, the overall activation energy for breakdown. The results have been compared with those for samples of the same polymers degraded in vacuum. The most thermally stable of the polymers examined under oxidizing conditions was poly(2,6‐dichlorophenylene oxide), with a stability comparable with that of a copolymer of tetrafluoroethylene and hexafluoropropylene.

The thermal degradation in vacuum of polymers containing aromatic or heterocyclic rings linked by various groups has been studied by a weight loss method. The most stable of the polymers examined were those with CO, mixed SO2 and O, orSO2 linkages. The stability of these were superior to or comparable with poly-p-phenylene and poly-m-phenylene. The particular combinations of aromatic nuclei and linking groups used did not result in tractability as most of the polymers were insoluble and infusible, even though of low molecular weight. Substitution in the aromatic nuclei could improve tractability, though at the expense of thermal stability.

The thermal degradation in vacuum of a number of halogenated poly(phenylene oxide) polymers has been studied by a weight loss method. In general the thermal stability decreased as the degree of substitution in the phenylene nuclei increased. The chloro derivatives were relatively more stable than the corresponding bromo derivatives. The majority of the polymers showed an initial rapid loss in weight followed by the formation of a highly stable residue. The good thermal stability of the simpler poly(phenylene oxides), coupled with their fusibility and solubility, indicate that they may be useful starting products for the preparation of practical materials.

AbstractThe thermal degradation in vacuum of a number of fluorine‐containing polymers has been studied by using a weight loss technique. The relative thermal stabilities of the different polymers have been determined and where possible the overall activation energy and frequency factors for their breakdown. The methods of assessment of the weight loss results are discussed. The most stable of the polymers are those which are fully fluorinated.