Synthetic polymers are a broad and versatile class of materials that are crucial to many areas of technology.  From aviation to biotechnology or from construction to packaging, polymers are ubiquitous in modern life and have been the focus of intense research for over a century. 

Securing patent protection for new developments in polymer science presents a particular set of challenges, especially at the European Patent Office (EPO).  The EPO can be very strict with requiring that the claims of European patent applications precisely define the invention.  However, as those working in this area will know, polymerisation can be a complex and unpredictable process, making it difficult to precisely define the chemical structure of the end product. 

With this in mind, here are our top tips for patenting polymer inventions at the EPO.

1. Product-by-process claims

While clearly defining the chemical structure of a polymer can be challenging, it is often more straightforward to define the process by which a polymer is made.  Polymers can be defined in European patent applications using “product‑by‑process” claims, e.g. “A polymer obtainable by the polymerisation of monomers Y and Z”.  This claim format still provides protection for the polymer itself and is routinely accepted by the EPO, provided that it can be argued that the polymer cannot be clearly defined in any other way.

2. Parameter pitfalls

Parameters defining measurable properties of a polymer, such as the molecular weight or the polydispersity, are another potentially useful tool for defining polymers in European patent applications.  However, care should be taken to ensure that the application precisely defines each parameter and includes a complete and unambiguous method for measuring it.  Otherwise, the application is vulnerable to a potentially fatal clarity objection from the EPO.

As an example, it is common to see polymers defined in patent applications in terms of their “molecular weight”.  However, there are different ways of defining the molecular weight of a polymer, such as the number average molecule weight (MN) or the weight average molecular weight (MW), which typically have different numerical values.  It is therefore important that European patent applications specify which definition of the molecular weight is intended in order to avoid clarity objections.

Further problems can arise if the application does not include a method for measuring the molecular weight.  There are many different methods known in the field for measuring the molecular weight of polymers, such as gel permeation chromatography (GPC) or light scattering techniques.  These different methods can provide different numerical values for the same polymer.  Defining a polymer by its molecular weight is therefore generally considered unclear by the EPO, unless the application specifies which method should be used to measure it, including any conditions that may affect the measurement.

Care should also be taken to avoid defining the polymer by what is known as a “result to be achieved”.  Simply using a parameter to claim all polymers with a desirable property, without specifying the features necessary to achieve this property, is unlikely to succeed at the EPO.  Where a polymer is defined using parameters, the claim should still include all the other essential features of the invention, for example structural features of the monomers or polymerisation conditions.

3. Consider what data might be needed to support your application

If patent protection is to be obtained for a polymer itself, the polymer must be different from, and a non-obvious modification of, known polymers.

At the EPO, the burden of proof is often shifted to the applicant to demonstrate that a novel manufacturing process results in a polymer that is itself novel, or that known polymers do not meet the parameters specified in a claim.  This usually involves generating data using various characterisation techniques.  For example, spectroscopic techniques could be used to demonstrate that the molecular structure of the polymer is different from known polymers.  Alternatively, a difference in the chemical structure of a polymer can be substantiated by evidence of a difference in the physical properties of the polymer.

Data showing advantageous properties of the polymer that are not suggested by the prior art can also be useful in convincing the EPO that the polymer is not an obvious modification of known polymers.  This is important for demonstrating a “technical effect” – a critical component for how the EPO assesses inventive step.

4. Strengthen your patent portfolio

Innovation may not only lie in structurally new polymers, but also in new uses of known polymers or processes for manufacturing them.  It is important to consider filing patent applications directed to these developments as well to strengthen your patent portfolio and improve your position against competitors.

If you would like to discuss the protection of your polymer inventions, please find my contact details on my web profile or get in touch with us at