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The molecular weight (MW) is the total atomic weight of a molecule. The MW is determined by summing the mass of all of the individual atoms in a molecule.

When considering polymers, molecular weights are generally expressed as average values such as Mn, (the number average molar mass), Mw (the weight average molar mass) and Mz (the z-average molar mass). The molecular weight of a polymer is expressed as an average, rather than an absolute figure, because polymer samples contain a mixture of chains of atoms of differing lengths.

The molecular weight of a polymer is directly related to its properties. As the molecular weight increases, mechanical properties generally increase.

Every polymer has an ideal molecular weight at which the balance of different properties (such as processability, strength, brittleness etc.) is optimized.

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Many devices and biopharma products are produced using polymers. If the molecular weight of the polymers used to build these products is not correct then device failure could occur.

The molecular weight of a polymer is typically determined using gel permeation chromatography (GPC), or size exclusion chromatography (SEC), alongside a refractive index or UV detector.

This method provides not only the average molecular weight values, but also information on the distribution of molecular weights in the polymer sample. GPC or SEC can also be coupled with additional detectors (such as a light scattering or viscometric detector) to provide information on the molecular architecture and size when in solution.

Viscosity measurements are also commonly used to gauge polymer molecular weight, but are less definitive.

GPC can provide detailed information about the polymer molecular weight distribution, whereas most other methods only provide a single average value.

Viscosity analysis, for example, provides the viscosity average molecular weight, Mv only. In addition, polymers can have similar average values but very different distributions (i.e. narrow, broad, bimodal) and this can result in product defects if not recognized. GPC is a great tool for the comparison of lot-to-lot variability, or for the determination of the likely suitability of a material for a given application.

Molecular weight is just one of the factors which impact the material properties of polymers. Other factors include the chemistry of the polymer(s), crystallinity, and which additives are present.

Sometimes it is stated that two polymers are identical based on a comparison of MW alone. This is a large oversimplification, which ignores many factors. MW alone cannot be used to obtain a reproducible polymer.

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Jordi Labs is an expert in the field of polymer chemistry. We provide more than just data; we provide answers to assist our clients in solving real-world problems. We understand polymer chemistry and can help our clients reach the root cause during a failure analysis. We can also help design fit-for-purpose devices and products.

As we move into the future, polymers are going to increase in complexity. This will require new tools and more advanced characterization methods to ensure product consistency lot-to-lot.

Ultra-high molecular weight polymers and increasingly complex polymer architectures will require improvements in GPC column technology, or alternative techniques, to prevent degradation during analysis and to resolve more subtle differences between polymers.

Dr. Anthony Grice is a Senior Scientist at Jordi Labs, a position he has held since 2014. During that time, Dr Grice has overseen over 600 successful analyses, and helped Jordi Labs continue its streak of 14 years of consecutive growth, and becoming a leader in the polymer analysis industry. Jordi now provides over 1500 analyses annually and offers more than 60 analytical techniques serving a wide range of industries including the pharmaceutical, medical device and chemical industries. Dr. Grice completed his combined bachelor’s and Master’s in chemistry at the University of Warwick in the United Kingdom. It was also at Warwick where Dr Grice obtained his Ph. D. under the supervision of Professor David Haddleton in the field of polymer chemistry, where he investigated emerging transition metal catalyzed living radical polymerization techniques (primarily SET-LRP). Following his PhD, Dr Grice managed a polymer characterization facility as part of the Science City Research Alliance, a strategic partnership between the University of Birmingham and the University of Warwick, where he provided a contract-based analytical service. His primary interests include complete polymer deformulation using chromatographic and mass spectrometric techniques, as well as polymer failure analysis and method development for the analysis of emerging polymer technologies.

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