The in-phase modulus and coefficient of diffusion of nylon 6 fibers are analyzed in terms of wide-and small-angle X-ray diffraction data. Both properties are examined in directions parallel and perpendicular to the fiber axis. The anisotropy in diffusion and mechanical coupling between the crystalline and amorphous phase reaches its maximum at relatively low draw ratios of about 2.5 to 3.0X. With increasing draw ratio the anisotropy in these properties decreases monotonically and reaches its minimum value with the fibers of the highest draw ratio (5.35X). The diffusion analysis yields a heretofore undetermined structural parameter, the separation of the microfibrils. The results indicate that increases in draw ratio lead t o an increase in the distance between the microfibrils, a decrease in the diameter to length of the crystallite, and a decrease in the diffusion constant of the permeable phase. The longitudinal structure of the microfibril is not affected significantly during this phase of drawing. These observations cannot be explained by the microfibrillar fiber model derived from studies of polyethylene and polypropylene fibers. A new structural model is proposed in which the strength, diffusion, and modulus are controlled by the densely packed matrix. The model is corroborated by transmission electron micrographs from thin fiber cross sections. be reproduced o r transmitted in any lormor by any means. electronic or mechanical, including photocopying. microfilming. and recording, or hy any information storage and retrieval system, without permission in wiling from the publisher.

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A piston‐cylinder‐type high‐pressure dilatometer has been built and the effect of pressure on melting behavior of poly(ethylene terephthalate) (PET) has been studied. The melting temperature increases but the rate of change of the melting temperature decreases with increasing pressure. Poly(ethylene terephthalate) crystallized from the melt at elevated pressure and temperature was studied by thermal analysis, and wide‐angle and small‐angle x‐ray diffraction and electron microscopy. Chain‐extended PET crystals were observed for the first time and some of their properties are described. A similarity to extended‐chain polyethylene is suggested.

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