Molecular Weight Averages and Polydispersity of Polymers

In this paper, we give a simple statistical argument to show that the polymer polydispersity index, the ratio of the weight-average molecular weight (WAMW) to the number-average molecular weight (NAMW), is directly related to the standard deviation of the polymer molecular weight distribution. There...

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Bibliographic Details
Published in:Journal of chemical education 2001-04, Vol.78 (4), p.554
Main Author: Sheu, Wen-Shyan
Format: Article
Language:English
Subjects:
Chemistry
Macromolecules
Molecular weight distribution
Molecules
Organic chemistry
Polydispersity
Polymers
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Summary:In this paper, we give a simple statistical argument to show that the polymer polydispersity index, the ratio of the weight-average molecular weight (WAMW) to the number-average molecular weight (NAMW), is directly related to the standard deviation of the polymer molecular weight distribution. Therefore, the polydispersity index can be used as a measure of the width of the molecular weight distribution, as addressed in textbooks. It is also shown that WAMW is never smaller than NAMW. This argument should help students to understand the physical meaning of the polydispersity index.
ISSN:0021-9584
1938-1328
DOI:10.1021/ed078p554