Showing papers in "Polymer Science U.s.s.r. in 1970"

Some features of the synthesis of polyimides by single-stage high-temperature polycyclization

Abstract: The synthesis of aromatic polyimides from the anhydrides of tetracarboxylic acids and diamines is carried out in two stages with the precipitation of an intermediate product (a polyamido-acid) in the first stage and its subsequent intramolecular molecular cyclodehydration which is carried out by heating or under the action of chemical agents [1]. Data exist about the synthesis of aromatic polyimides in phenols at elevated temperatures in the presence of tertiary amines [2], and about the synthesis of polyimides from 2,3,5,6-pyridinetetracarboxylic acid in polyphosphoric acid at a temperature below 180°C [3]. With soluble polyimides of anilinephthalein as an example, we have previously [4, 5] developed a new method of synthesizing polyimides, by single-stage high-temperature polycyclization in an organic solvent; the method consists of interaction between a diamine and the dianhydride of a tetracarboxylic acid in a high-boiling solvent at 190–210°C. Subsequently, this method was extended to the synthesis of other polyides with different chemical structures [5–7]. The comparison which we made between the single-stage method and the two-stage method widely used at the present time brought to light certain advantages of single-stage polycyclization. The present communication is devoted to the study of certain rules governing the synthesis of polyimides by single-stage polycyclization, the reaction between pyromellitic dianhydride (I) and 3,3-bis-(4-aminophenyl) phthalide (anilinephthalein) (II) in nitrobenzene being used as the example. Moreover, the possibility of adapting this method to polymers which are insoluble or swell in the reaction medium, by varying the nature of the organic solvent and the chemical structure of the polyimide, has been discussed.

The effect of stretching on the macromolecular structure of polymer fibres

Abstract: The increase of the degree of stretching, W, of previously oriented fibres, produced from different crystalline polymers, results in an intensity decrease of the meridianal reflection, I, in low-angle X-ray scattering pictures [1–3]. The same phenomenon was described elsewhere [4] when polyvinyl alcohol (PVA) fibres were stretched at near-melting temperatures. A series of independent measurements of a whole series of structural parameters associated with changes I established that all these changed only slightly [4]. One parameter, not directly measured, which had more effect on I was the density difference between crystalline and amorphous zones, pc−pa; the main part of the reduction in I was therefore attributed to the compensation of this difference [4]. By combining the low-angle X-ray scattering with a fibre shaded with iodine [5], we tried to verify the earlier conclusion that the intrafibrillar amorphous zones become denser, and to evaluate their density. The term “intrafibrillar” is defined as being the zones which directly affect I by their density and dimensions. The remaining unordered zones of the polymer were named interfibrillar.

Electron-microscopical and electron diffraction study of the deformation of thin films of spherulitic polyvinylidenefluoride☆

Abstract: It is well known that spherulites are the most common and at the same time the most complex structural form produced in crystallizable polymers when they are crystallized from solution or the melt [1]. Naturally therefore research workers have been interested in recent years in study of the structure of spherulites, in the mechanism of their deformation and in their structure in the orientated state, using for this purpose the methods of optical and electron microscopy, and optical, X-ray and electron diffraction (wide and low angles), etc. According to some authors [2–4] the deformation of spherulites involves breakdown of the original structure and formation of a new fibrillar structure, depending on the conditions of deformation. In papers by Kargin and his collaborators it is shown that in addition to the above mechanism deformation of spherulites can occur in stages with breakdown of more complex structures while the simple structural elements are preserved [5, 6]. A considerable degree of reversible deformation of spherulites is also possible under certain conditions [5]. All this shows that depending on the conditions of deformation, the chemical structure of the polymer and its previous treatment, the deformation of spherulites can follow different patterns. Because of the complexity of this problem neither the mechanism of deformation of spherulites [7] nor the structure of orientated crystalline polymers [8] have yet been completely clarified. These problems have been examined most thoroughly in a recent series of papers by Peterlin and his collaborators [9–18] and by Kabayashi and Nagasawa [19], in which the deformation of single crystals, thin spherulitic films and block specimens of polyethylene (PE) was studied. The occurrence of periodicity along fibrils in block specimens and thin films of PE was observed in the electron microscopy by Peterlin and his collaborators, who to increase the contrast made use of the methods of etching with fuming nitric acid and shadowing of thin films and replicas. Only in fibrils drawn from PE single crystals was it possible to observe fairly clear periodicity [20], In the same specimens, after they had been annealed at temperatures above 120 electron diffraction analysis showed a long period corresponding to the periodicity observed in the electron microscope. The long periods first found by Basset and Keller [21] by electron diffraction in the electron microscope, in stretched block specimens of PE (500–5000 A) scarcely correspond to the real amorphous-crystalline structure of the polymer, and are obviously due to unsuitable choice of the etching conditions. We have shown previously [22] that it is possible to observe in the electron microscope, and by low-angle diffraction, long periods in stretched and then annealed spherulitic films of polyvinylidenefluoride (PVF2) that have not received any additional treatment (shadowing, etching etc.) for the purpose of increasing the contrast in the electron microscope. The present paper presents the results of an electron-microscopical and electron diffraction (low and wide angles) study of thin spherulitic films of PVF2, stretched at various temperatures and also subsequently annealed.

Heat resistance of polymers

Abstract: 1. J. H. SAUNDERS and K. K. FRISCH, Khim. poliuretanov (Polyurethane Chemistry). Izd. "Khimiya", 1968 2. W. BERLENT and A. HOFFMAN, Graft Copolymers and Block Copolymers, 1963 3. Sintez i fizikokhimiya poliuretanov (Synthesis and Physicochemistry of Polyurethanes). Izd. "Naukova dumka", 1967 4. M. Sh. YAGFAROV, Dokl. An SSSR 179: 581, 1968 5. E. F. GUBANOV, A. G. SINAISKII, N. P. APUKHTINA and B. Ya. TEITEL'BAUM, Dokl. AN SSSR 168: 1151, 1965 6. A. A. TAGER, Fiziko-khimiya polimerov (Physicochemistry of Polymers). Izd. "Khimiya", 1968 7. M. Sh. YAGFAROV, Vysokomol. soyed. A10: 1267, 1968 (Translated in Polymer Sci. U.S.S.R. 1O: 6, 1465, 1968) 8. V. A. KARGIN and G. L. SLONIMSKII, Kratkie ocherki po fiziko-khimiya polimerov (Short Notes on the Physicoeheznistry of Polymers). Izd. "Khimii", 1967 9. B. Ya. TEITEL'BAUM, Dokl. AN SSSR 181: 368, 1968 10. E. F. GUBANOV, B. Ya. TEITEL'BAUM, A. G. SINAISKII and N. P. APUKHTINA, Dokl. AN SSSI~ 179: 621, 1968