Polymer REACH: Pray or be Prepared? A Polymer Chromatography Viewpoint on What to Expect

Timo F. Beskers previews his tutorial lecture at HPLC 2023 in Düsseldorf, where he will give an overview on polymer REACH, its expected regulatory requirements, challenges, and analytical needs, as well as strategies to deal with those from the perspective of polymer chromatography.

Little is known about the details of the upcoming EU legislation called polymer REACH (PREACH). This makes planning and preparation difficult for the polymer analytical community. But can we just wait for more reliable details on the requirements, or do we need to prepare already? And how can we prepare for the unknown?

Polymers are large molecules, composed of similar or identical repeating units, called monomers. Due to the nature of their synthesis, polymer materials show distributions in many properties, of which molecular weight is the most important one. Whilst measuring a broad range to get information about the distribution instead of determining a single value often poses an analytical challenge, it is exactly these distributions that allow polymers to have many different and very versatile properties, and to be fine‑tuned for their specific applications. That, together with their ease of production, is why polymers are so ubiquitous and essential to the life we know today.

The omnipresence of polymers comes with downsides, which often appear beyond their intended purpose. Polymers are used so frequently in everyday life that they constitute a significant part of global waste production: directly post-lifetime, but also through abrasion and breakage, for example. Not only the polymer itself but also side components and impurities in the polymer materials can be released into the environment. This has become a grave concern globally, and actions are being taken to mitigate or prevent it. The European Commission included polymer registration and risk assessment as a focus area within the Chemicals Strategy for Sustainability (CSS) in its Green Deal, an initiative to transform into a climate neutral, sustainable, and circular economy (1).

To enable risk assessment of polymers, the REACH (Registration, Evaluation, Authorisation and Restriction of Chemicals) legislation will be extended. This so‑called polymer REACH is expected to be put into force soon. The first timeline proposals suggested an entry into force in 2022, which has been postponed to 2026 (2). These developments will have a huge impact on the 300 billion EUR polymer market in Europe. The registration of polymers is expected to be a complex process, as a lot of analytical and eco‑toxicological data need to be generated.

Different registration scenarios are being discussed, but a volume in the order of 200,000 polymers are expected to be notified to the European Chemicals Agency (ECHA), of which—depending on the extent of allowed grouping—at least 30,000 will require a full registration (3). This number significantly exceeds the approximately 23,000 substances that were registered under REACH by 2022. The regulatory costs for registering polymers in the EU will easily accumulate to many billions of euros within the next decade.

To date, the exact data requirements for PREACH are still unknown, but what can the polymer industry expect and what should analytical laboratories prepare for?

Molecular weight distribution (MWD) will be one key characteristic and will already be required for the notification of polymers. MWD needs to be analyzed by size-exclusion chromatography (SEC) or gel permeation chromatography (GPC), which are described in the Organisation for Economic Co-operation and Development (OECD) test guidelines 118 and 119 (or similar DIN and ISO norms) (4–13). A technical requirement for SEC is solubility, so only soluble polymers can be analyzed for their MWD and the mean molar mass values M_n and M_w derived from it. For crosslinked or ultrahigh-molecular-weight polymers, only the soluble fraction can be analyzed. Under the assumption that all insoluble parts are of a high molecular weight, M_n and M_w are underestimated and the even more important oligomer content (amounts <500g/mol and <1000g/mol) is overestimated. While this provides values for a worst-case risk assessment and might look like a pragmatic approach to a toxicological evaluation, analyzing as little as only 10% of your sample is not a fair representation of the whole sample and easily ends up with results below (or above) the specific regulatory threshold. This can be decisive if registration is required or not and therefore can lead to more animal testing, with only limited knowledge gain.

Another important analytical task is the measurement of water solubility and the partition coefficient between a water and an octanol phase (log P_ow or log K_ow), as these values indicate the bioavailability and bioaccumulation potential of the substance. What might seem like a simple analytical task is actually very complex. As a polymer material is a collection of many different, similar but not identical, molecules, the material is not characterized by a single water solubility, but by a distribution of solubilities. In general, lower molecular weight fractions are more soluble than longer polymer chains. Therefore, the soluble fraction is again not representative of the complete polymer material. For very low solubilities, it is very likely that only the impurities in the material dissolve, which are not polymers at all. Identification of the dissolved part, especially for low concentrations, is very tricky, as most sensitive methods like mass spectrometry (MS) or gas chromatography (GC) show a strong molar mass dependence or are not suitable for polymer molecules at all. The OECD 105 for water solubility is therefore only suitable for small molecules and should be adjusted for polymers or supplemented by a separate guideline (14). Similar considerations apply for the determination of the log P_ow and OECD 107 (15). The alternative guideline OECD 117 (16) suggests a high performance liquid chromatography (HPLC) method to correlate the retention of the sample with those of reference substances with known log P_ow values. Polymer separations in HPLC are governed not only by polarity but also by solubility. Or in other words, polymer separations in HPLC show a molar mass dependence. This limits the applicability domain of the method considerably and questions the validity of low P_ow values derived by the OECD 117.

Universal methods that can be applied to all polymers do not exist for all relevant properties required for PREACH. It is not only in the chromatography field that it is challenging to find or develop suitable methods for polymers that also fulfill the regulatory requirements.

The problem at hand is the very individual nature of polymer materials that often requires tailored analytical approaches. On the other hand, there is a regulatory need for standardized, fast, universally applicable, and validated methods to be used in the PREACH registration process. These conflicting requirements pose very big challenges for the analytical community, which should be tackled with proactive preparation. Without development of new methods and strategies, as well as suggestions for guidelines and general procedures, the registration of polymers will be difficult and costly. A strategy of waiting and hoping for the best will not only result in the loss of important polymer products and markets in the EU, but also lead to more eco-toxicological tests, a situation that could be remedied by the availability of better methods and testing strategies.

References

1. European Commission, Directorate-General for Communication. European Green Deal: Delivering on our Targets; Publications Office of the European Union, 2021. DOI: 10.2775/373022
2. European Commission, Directorate-General for Internal Market, Industry. Entrepreneurship and SMEs. Transition Pathway for the Chemical Industry; Publications Office of the European Union, 2023. DOI: 10.2873/873037
3. European Commission, Directorate-General for Environment, Bougas, K.; Corden, C.; Crookes, M.; et al. Scientific and Technical Support for the Development of Criteria to Identify and Group Polymers for Registration/Evaluation Under REACH and Their Impact Assessment: Final Report; Publications Office, 2020. DOI: 10.2779/890644
4. OECD, Test No. 118: Determination of the Number-Average Molecular Weight and the Molecular Weight Distribution of Polymers using Gel Permeation Chromatography; OECD Guidelines for the Testing of Chemicals, Section 1, OECD Publishing, 1996. DOI: 10.1787/20745753
5. OECD, Test No. 119: Determination of the Low Molecular Weight Content of a Polymer Using Gel Permeation Chromatography; OECD Guidelines for the Testing of Chemicals, Section 1, OECD Publishing, 1996. DOI: 10.1787/20745753
6. DIN EN ISO 13885-1:2021-11, Gel permeation chromatography (GPC) - Part 1: Tetrahydrofuran (THF) as eluent (ISO 13885-1:2020). DOI: 10.31030/3291399
7. DIN EN ISO 13885-2:2021-11, Gel permeation chromatography (GPC) - Part 2: N,N-Dimenthylacetamide (DMAC) as eluent (ISO 13885-2:2020). DOI: 10.31030/3291394
8. DIN EN ISO 13885-3:2021-11, Gel permeation chromatography (GPC) - Part 3: Water as eluent (ISO 13885-3:2020). DOI: 10.31030/3291393
9. ISO, ISO 16014-1:2019-05, Plastics - Determination of average molecular weight and molecular weight distribution of polymers using size-exclusion chromatography - Part 1: General principles.
10. ISO, ISO 16014-2:2019-05, Plastics - Determination of average molecular weight and molecular weight distribution of polymers using size-exclusion chromatography - Part 2: Universal calibration method.
11. ISO, ISO 16014-3:2019-05, Plastics - Determination of average molecular weight and molecular weight distribution of polymers using size-exclusion chromatography - Part 3: Low-temperature method.
12. ISO, ISO 16014-4:2019-05, Plastics - Determination of average molecular weight and molecular weight distribution of polymers using size-exclusion chromatography - Part 4: High-temperature method.
13. ISO, ISO 16014-5:2019-05, Plastics - Determination of average molecular weight and molecular weight distribution of polymers using size-exclusion chromatography - Part 5: Light-scattering method.
14. OECD, Test No. 105: Water Solubility; OECD Guidelines for the Testing of Chemicals, Section 1, OECD Publishing, 1995. DOI: 10.1787/20745753
15. OECD, Test No. 107: Partition Coefficient (n-octanol/water): Shake Flask Method, OECD Guidelines for the Testing of Chemicals, Section 1, OECD Publishing, 1995. DOI: 10.1787/20745753
16. OECD, Test No. 117: Partition Coefficient (n-octanol/water), HPLC Method; OECD Guidelines for the Testing of Chemicals, Section 1, OECD Publishing, 2022. DOI: 10.1787/20745753

Timo F. Beskers’ career in polymer chromatography started at the Karlsruhe Institute of Technology in 2010. There, he obtained his Ph.D. in 2014 under the supervision of M. Wilhelm on the topic of chemically sensitive detectors for SEC. After a postdoc with H. Pasch at Stellenbosch University, Timo started working for PSS Polymer Standards Service GmbH, a company specialized in SEC. He is now leading an analytical SEC laboratory at BASF SE. His research interests lie in method development, two-dimensional or coupled techniques, and polymer analytics for regulatory requirements: OECD, DIN or ISO guidelines, GLP, and preparation for polymer REACH.

Timo F. Beskers will present his tutorial on Monday 19 June at 14:30 in Room 3.