The crystal structure of nylon I2 was determined from the X-ray diffraction patterns of uniaxially oriented specimens. The unit cell is monoclinic (pseudo-hexagonal) with the following dimensions: a = 4,79 if, b = 31,9 A (fiber axis), c = 9,58 if, B = 120". There are four monomeric units in the unit cell and the space group is P21/c. The structure presents a distortion of the amide group from the planar chain conformation and it is rather similar to y-nylon 6. The hydrogen bond length is about 2 , 8 0 A and the molecular packing is characterized by alternate, "up and down", highly disordered sheets of parallel chains, linked by hydrogen bonds. The agreement between observed and calculated intensities has been improved by introducing a statistical disorder. ZUSAMMENFASSUNG:Die KristaIIstruktur von Nylon-I2 wurde mit Hilfe von Rontgenbeugungsdiagrammen uniaxial orientierter Praparate bestimmt. Die Elementarzelle besitzt eine monokline (pseudo-hexagonale) Symmetrie mit den Parametern a = 4,79 A, b = 31,9 if (Faserachse), c = 9,58 if, = 120'. Die Zelle enthalt 4 monomere Einheiten; die Raumgruppe ist P21/c. Die Amidgriippen sind gegeniiber der Ebene der planaren Zick-zack-Kette verdreht. Fur die Lange der Wasserstoffbindung ergibt sich ein Wert von etwa 2,80if. Die Struktur scheint der y-Form des Nylons-6 ahnlich zu sein. Parallel laufende Molekiile sind durch Wasserstoffbriicken verbunden und bilden sog. Rostebenen; diese sind mit einem hohen Unordnungsgrad antiparallel angeordnet. Die Ubereinstimmung zwischen den beobachteten und den berechneten Intensitaten konnte durch die Annahme einer statistischen Unordnung verbessert werden.

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synopsisThe influence of crystallinity, thermal history, plasticization, copolymerization, and chemical modifications on the dynamic-mechanical properties of poly ( vinyl chloride) has been studied by means of a free-oscillation torsional pendulum. It was found that the secondary dispersion maximum is not affected by free volume, crystallinity, or bead-to-head microstructure, but is modified by post-chlorination, copolymerization, and plasticization. These results show that the molecular motions responsible for the PVC @ peak are not influenced by local differences in the distribution of the C1 atoms along the chain, so that they seem to be largely of a cooperative type.

Some structurally disordered models for poly(tetrafluoroethy1ene) were elaborated and the corresponding calculated X-ray diffraction patterns compared with experimental patterns. This and differential scanning calorimetry results suggest some differences between the virgin powder and a sintered polycrystalline plate of poly(tetrafluoroethy1ene). These differences may be related to the crystal phase transitions that occur in a range of temperatures close to room temperature.