About Molecular Weight Analysis

Polymers inherently have a distribution of chain lengths resulting in a molecular weight distribution. Molecular weight is the size of the molecules that comprise a plastic or rubber material.  The properties of the polymer during processing and in the application are influenced by the polymer's molecular weight distribution.  For example, lower molecular weight chains help improve melt processing, while the higher molecular weight fraction can be critical to mechanical properties. Additionally, molecular properties vary over the life cycle of a material.  The molecular weight value of a polymer will change as the polymer progresses through stages such as raw material, molding, sterilization, and storage.

  • Applications

    The solubility of a polymer material is a critical parameter to be determined when choosing an analytical method for measuring molecular weight.

    We regularly use the following testing capabilities used to conduct Molecular Weight Analysis:

    • Gel Permeation Chromatography/Size Exclusion Chromatography (GPC/SEC)
    • Gel Permeation Chromatography in Hexafluoroisopropanol (HFIP)
    • Inherent and Intrinsic Viscosity (IV)
    • Melt Rheology
    • Melt Flow Index (MFI)

    The method that provides the most information regarding the molecular weight of a polymer is Gel Permeation Chromatography (GPC), also known as Size Exclusion Chromatography (SEC). GPC/SEC provides you with the molecular weight distribution and depending on the type of calibration will provide you with relative molecular weight values to known standards or absolute molecular weights. This method can be used for determining the level of low molecular weight chains for instance in the range of 1,000 g/mole or less by using a slice table methodology for the calculations.

    One of the most broadly useful techniques for comparing or specifying molecular weight limits is Dilute Solution Viscosity (IV).  Inherent Viscosity and Intrinsic Viscosity can be used for specification purposes or release purposes but they will not provide you the critical distribution information that may be required in initial research investigations or in full qualification of a material.

    In some instances the requirement is to measure a material per a specification which calls for a Melt Flow Index (MFI) value.

  • Sample Considerations

    Sample submission will depend on the Molecular Weight Analysis technique used. 

    Contact us to determine the proper technique and associated sample considerations.

  • Experience

    Our extensive experience determining molecular weight includes prodcuts and materials such as:

    • Stents
    • PLGA coated stents
    • Cellulose
    • Chitosan
    • Fluropolymers
    • Polysaccharaides
    • Vicryl mesh
    • Polypeptides
    • Various resins such as polycarbonate, nylons, and PETs
    • Nylon copolymers
    • Ultrahigh molecular weight polyethylene for medical products
    • Nitrocellulose used for ammunition and explosives applications
    • Polyphenylene sulfide for products requiring an engineering resin, such as automotive products and medical devices