Essentials Of Materials Science And Engineering
Essentials Of Materials Science And Engineering
4th Edition
ISBN: 9781337385497
Author: WRIGHT, Wendelin J.
Publisher: Cengage,
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Chapter 16, Problem 16.44CP
Interpretation Introduction

Interpretation:

The average molecular weight and degree of polymerization for the given data of polyethylene are to be calculated.

Concept Introduction:

The molecular weight of a polymer is not fixed. It has a certain range under which its molecular weight falls. For a linear polymer, degree of polymerization represents the average length of the polymer. Degree of polymerization is defined as:

  Degree of polymerization=average molecular weight of polymermolecular weight of repeating unitn= ( MW ) av. ( MW ) repeating unit    .... (1)

Weight average molecular weight (M¯w) of a polymer is calculated by the formula:

  M¯w=fiMi    .... (2)

Here, fi is the weight fraction polymer chains in the size range i and Mi is the mean molecular weight of that size range.

Number average molecular weight (M¯n) of a polymer is calculated by the formula:

  M¯n=xiMi    .... (3)

Here, xi is the fraction of total polymer chains in the size range i and Mi is the mean molecular weight of that size range.

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