摘要:

When cotton hydrocellulose I is extracted with refluxing aqueous 0.6 M sodium hydrogen carbonate, alkali-catalyzed depolymerization occurs, causing a 40% loss of weight. An overalldecreasein x-ray diffractive crystal-Unity of the residue has been previously reported. However, since degradation is presumed to occur preferentially in a less-ordered or “amorphous” domain of the polymer, anincreasein crystallinity would have been expected. We have now shown that a diminished crystallinity index is exhibited by replicate samples, but does not occur during refluxing in the absence of alkali. Furthermore, it is not an artifact caused by drying conditions or by environmental or instrumental instability during measuring. The anomalous change in crystallinity may be accounted for by an increase in the ratio of surface area to volume of crystallites during degradation. A higher ratio would necessarily produce a decrease in crystallinity through an enhanced contribution from the disordered surface component to the scattering. Experimental evidence for this hypothesis is provided by the decrease now found in the effective lateral crystallite dimension perpendicular to the 002 plane.

ISSN:0022-2348    

DOI:10.1080/00222348508248024

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

Accurate measurement of intensity data from x-ray diffraction patterns of oriented fibers is one of the major difficulties in the determination of polymer structures. Accurate diffraction data are particularly important when discrimination between different, but similar, molecular models is required. Although digital processing of diffraction patterns has provided more accurate data than was obtainable by traditional measurements, many of the methods used have been partly subjective and restricted to well-resolved diffraction patterns. Background is a major source of error in intensity measurement. A general method of two-dimensional background removal has been developed. Objective methods of measuring the intensities of Bragg reflections from x-ray diffraction patterns of polycrystal-line fibers are described. A profile fitting method (which is an extension of the previously reported angular deconvolution procedure) for measuring diffraction data from noncrystalline oriented polymers is also presented. These methods have been used to collect data from diffraction patterns of a variety of nucleic acid polymers.

ISSN:0022-2348    

DOI:10.1080/00222348508248025

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The previous Polymer Diffraction Symposium saw the use of x-ray film data array calculations to obtain diffraction intensities with computed accuracies. Subsequently, methods for geometrical deconvolution of overlapped diffraction spots have been developed. The techniques have now been applied to data arrays from films of Fortisan. Severely overlapped reflection arcs were splined and transformed into polar coordinate space, yielding orthogonalized diffraction spot groups. Spots were then identified

ISSN:0022-2348    

DOI:10.1080/00222348508248026

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

ISSN:0022-2348    

DOI:10.1080/00222348508248027

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor

摘要:

The Symposium on Polymer Diffraction was part of the 188th National Meeting of the American Chemical Society held in Philadelphia, Pennsylvania, in August 1984 under the sponsorship of the Cellulose, Paper, and Textile Division and the Division of Polymeric Material: Science and Engineering.

ISSN:0022-2348    

DOI:10.1080/00222348508248013

出版商:Taylor & Francis Group    

年代:1985

数据来源: Taylor