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The ratio of the weight-average and number-average molecular weights, \[ \dfrac{\overline{M}_w}{\overline{M}_n} \] is a measure of the polydispersity of a polymer mixture - how widely distributed the range of molecular weights are in the mixture.
Organized by textbook: https://learncheme.com/ Calculates average molecular weight using a mass basis and a molar basis. Made by faculty at the University of...
The molecular weight is just the total weight divided by the number of molecules. This quantity is called the number average molecular weight, or M n Exercise \(\PageIndex{3}\)
The average molecular weight of a polymer sample can be determined using a variety of techniques, such as gel permeation chromatography, light-scattering measurements and viscosity measurements, and the type of average that is yielded depends on the technique.
The number average molecular weight is the total weight of the sample divided by the number of molecules in the sample. What's the total weight of the sample? First find the total weight of each type (or weight) of polymer.
Two experimentally determined values are common: Mn M n, the number average molecular weight, is calculated from the mole fraction distribution of different sized molecules in a sample, and Mw M w, the weight average molecular weight, is calculated from the weight fraction distribution of different sized molecules. These are defined below.
Molecular weight is the sum of the atomic weights of all atoms in a molecule's chemical formula. Like atomic weight, it represents the mass of a single molecule and is expressed in atomic mass units (amu) or Daltons (Da).
One set of methods gave something called the number average molecular weight (symbol M n). These methods essentially took the weight of a sample, counted the molecules in a sample, and therefore found the average weight of each molecule in that sample.
A simple compound has a fixed molecular weight; for example, Acetone has 58 molecular weights. Suppose this 58 molecular weight becomes 60; then the compound is no longer Acetone but may be acetic acid. Each molecule has the same molecular weight. It is valid for all low molecular-weight compounds.
The equation $$ mw = \frac{\sigma(w_i m_i)}{\sigma w_i} $$ defines the molecular weight average, which is a crucial concept in understanding polymer science. This formula calculates the average molecular weight of a polymer sample based on the contribution of each component's molecular weight and its proportion within the mixture.