The Definition of Polymer Molecular Weight

The Definition of Polymer Molecular Weight

Image Credit: Jordi Labs

The molecular mass of a polymer chain is known as the polymer molecular weight (MW). Polymer chains exhibit different characteristics, while small molecules of the same elemental composition all have the same molecular weight.

These chains are compounded from a variety of small molecules which can modify the mechanical behavior of the polymer and skew its molecular weight. This makes it almost impossible to establish a consistent molecular weight for synthetic polymer chains.

A bell curve distribution is employed to establish polymer molecular weights and calculate an average value for synthetic polymer chains. To ascribe a numeric value for the molecular weight distribution of polymer chains, three distinct molecular weight averages are utilized:

  • The Z average molecular weight (Mz), which describes the highest portion of molecular weight of the sample
  • The weight average molecular weight (Mw), which describes the average that is closest to the center of the bell curve
  • The number average molecular weight (Mn), which describes the lowest portion of molecular weight of the sample

The Importance of Polymer Molecular Weight

The physicochemical properties of a polymer are wholly dependent upon the molecular weight and its distribution throughout the polymer chain. Consistency is vital for many manufacturers in pharmaceutical, litigation, biotech, and petroleum industries.

The properties of commercial polymers are also dependent on the molecular weight of the chains utilized in their construction. Products such as food packaging and car parts depend upon ductile materials, which possess good plastic deformation to withstand rugged daily use.

Polymeric materials are varied fundamentally. Those made up of a low amount of repeated units, and so a low molecular weight, usually have soft or even fluidic properties with little mechanical strength.

On the other hand, larger chains with increased molecular weight exhibit solid properties with much better physical integrity than their shorter chain counterparts. These properties can establish the melting and softening points of a polymeric product, its elasticity, and its solution and melt viscosity.

Establishing Polymer Molecular Weight

Molecular weight is found by multiplying the mass of each subsequent repeating unit in the polymer chain, before adding the mass of either end group. This supplies a variety of values which can be utilized to determine the molecular weight distribution of the material.

The most common value of merit for manufacturers is the average molecular weight, but the high and low portion molecular weights are also crucial for understanding the complete distribution curve and determining the broader characteristics of the polymer.

The processing properties of polymeric materials are mainly established by their molecular weight distribution, with narrower distribution curves usually suggesting better mechanical and processing properties compared to broader distributions.

This is because of the plasticizing influences of the low portion molecular weight that softens the material, while the high portion disproportionately contributes to the melt viscosity.

Molecular Weight Distribution with Jordi Labs

Jordi Labs supplies unparalleled expertise in the field of molecular weight analysis, utilizing cutting-edge chromatographic methods to establish polymer molecular weight distributions with outstanding degrees of accuracy.

It uses Gel Permeation Chromatography (GPC) to establish the polymeric molecular weight distributions for a wide variety of products.

This information has been sourced, reviewed and adapted from materials provided by Jordi Labs.

For more information on this source, please visit Jordi Labs.

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