All OECD countries use the OECD Polymer Definition as developed in 1990, whereas some countries transposed it into more quantitative terms:

“A 'POLYMER' means a substance consisting of molecules characterized by the sequence of one or more types of monomer units and comprising a simple weight majority of molecules containing at least three monomer units which are covalently bound to at least one other monomer unit or other reactant and consists of less than a simple weight majority of molecules of the same molecular weight. Such molecules must be distributed over a range of molecular weights wherein differences in the molecular weight are primarily attributable to differences in the number of monomer units. In the context of this definition a 'MONOMER UNIT' means the reacted form of a monomer in a polymer.”

Under REACH, the following definitions are provided (Article 3):

• Monomer: "a substance which is capable of forming covalent bonds with a sequence of additional like or unlike molecules under the conditions of the relevant polymer- forming reaction used for the particular process (Article 3(6))."
• Polymer: "a polymer is a substance consisting of molecules characterised by the sequence of one or more types of monomer units. Such molecules must be distributed over a range of molecular weights. Differences in the molecular weight are primarily attributable to differences in the number of monomer units."

In accordance with REACH (Article 3(5)), a polymer is defined as a substance meeting the following criteria:

• Over 50 percent of the weight for that substance consists of polymer molecules (see definition below); and,
• The amount of polymer molecules presenting the same molecular weight must be less than 50 weight percent of the substance.

A further clarification of the definition of a polymer substance is provided in the ECHA Guidance on monomers and polymers.

So far, polymers as such are exempt from the registration obligation (Title II) and the evaluation (Title VI) under REACH (Article 2(9)), but registration is required for monomers and other substances comprising the polymer, if (Article 6(3) REACH):

• The polymer consists of 2% weight by weight (w/w) or more of such monomer substance(s) or other substance(s) in the form of monomeric units and chemically bound substance(s); and
• The total quantity of such monomer substance(s) or other substance(s) makes up 1 tonne or more per year (the total quantity in this context is the total quantity of monomer or other substance ending up chemically bound to the polymer).

Although substances used as monomers in the manufacturing of polymers are by definition intermediates, they cannot be registered in accordance with the provisions which normally apply to on-site or transported isolated intermediates (Article 6(2)). In contrast, Articles 17 and 18 (on intermediates) do apply to the other substances (e.g. initiators, terminators, chain-transfer agents, post-reactants) used in the manufacture of the polymer.

It is worth noting that polymers are not exempted from the CLP Regulation. A polymer is a substance and as such has to be notified when placed on the market in cases where it fulfils the criteria for classification as hazardous (Article 39(b) CLP).

Polymers could be required to be registered at some point in the future. According to Article 138(2) REACH, the European Commission (EC) may come up with a legislative proposal to amend REACH requesting registration of a range of selected polymers.

Notably in other OECD countries, legislative regimes normally include provisions for polymers, whereas the concept of “Polymers of Low Concern” (PLC) is integrated. PLCs are assumed to have insignificant impact on human health and the environment.

Within the REACH review (process to identify potential needs to amend REACH), the possibilities of polymer registration requirements were assessed. Based on a first study (Risk & Policy Analyst Limited, 2012), the EC identified two registration approaches for further investigation: (i) Grouping polymers for registration, and (ii) defining a category (or categories) of polymers of low concern.

A further study analysed existing approaches outside the EU and proposed alternative options (other than the current one of no registration) which could be used in the EU and preliminarily assess feasibility and cost-effectiveness of these options. The final report (BIO by Deloitte, 2014) is available here.

The final decision on the polymer registration must try to minimise the costs for industry including those for innovation and competition, while maximising the benefits to human health and the environment. The recent studies mentioned above contribute to the conclusion that polymers might face additional regulatory requirements in the future.