A Guide to Polymer Molecular Weight

Polymer Molecular Weight

Image Credit: Jordi Labs

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

These chains are compounded from numerous small molecules that can change the mechanical behavior of the polymer and skew its molecular weight. This makes establishing a consistent molecular weight for synthetic polymer chains nearly impossible.

A bell curve distribution is employed to establish polymer molecular weights and identify an average value for synthetic polymer chains. Three distinct molecular weight averages are utilized in order to attribute a numeric value for the molecular weight distribution of polymer chains:

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

The Importance of Polymer Molecular Weight

The physiochemical properties of a polymer are totally dependent upon the molecular weight and its distribution throughout the polymer chain. Consistency is key for many manufacturers in hugely varying sectors like the biotech, pharmaceutical, litigation, and petroleum industries.

The characteristics of commercial polymers are also dependent upon the molecular weight of the chains that are utilized in their construction. Products like food packaging and car parts depend upon ductile materials that show good plastic deformation to withstand rugged daily employment.

Fundamentally, polymeric materials are varied. Those that are made up of a low number of repeated units, and therefore, low molecular weight, usually have soft or even fluidic properties with little mechanical strength.

Yet, larger chains with more molecular weight exhibit solid properties with hugely enhanced physical integrity over their shorter chain counterparts. These properties can establish the softening and melting points of a polymeric product, its melt viscosity and solution, and its elasticity.

Determining Polymer Molecular Weight

Molecular weight is established by multiplying the mass of each subsequent repeating unit in the polymer chain before adding the mass of either end group. This provides a range of values that 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. Still, the high and low portion of molecular weights are also crucial for understanding the entire distribution curve and determining the broader characteristics of the polymer.

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

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

Molecular Weight Distribution with Jordi Labs

In the field of molecular weight analysis, Jordi Labs provides unparalleled expertise, employing cutting-edge chromatographic methods to establish polymer molecular weight distributions, with outstanding degrees of accuracy. Jordi Labs employs Gel Permeation Chromatography (GPC) to establish polymeric molecular weight distributions for a wide range 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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