The First Meeting of the Expert Group on Polymer Definition held in Toronto, Canada (January 1990), developed the polymer definition.

The Second Meeting of the Expert Group on Polymer Definition held in Paris, France (October 1991), reconfirmed the agreed definition.

In the document, Second Meeting of the OECD Expert Group on Polymer Definition: Chairman's Report [ENV/MC/CHEM(91)18], it is stated in paragraph 5:

In considering the report and subsequent comments the Group reconfirmed the agreed definition on polymers for use in new chemicals notification procedures i.e.":

An OECD definition developed to distinguish discrete substances from polymers:

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."

Third Meeting of OECD Experts on Polymers, held in Tokyo, Japan (April 1993), further clarified some of the terms of the definition to avoid ambiguity and set criteria of importance for identifying polymers of low concern.

In the document, Third Meeting of the OECD Experts on Polymers: Chairman's Report [ENV/MC/CHEM/RD(93)4], it is stated in paragraph 8:

The Working Group recommended the following addition to the polymer definition.

Sequence: means that the monomer units under consideration are covalently bound to one another and form a continuous string within the molecule, uninterrupted by units other than monomer units.

Monomer: means a molecule which is capable of forming covalent bonds with two or more like or unlike molecules under the conditions of the relevant polymer-forming reaction used for the particular process.

Other reactant: means a molecule linked to one or more sequences of monomer units but which, under the relevant reaction conditions used for the particular process, cannot become a repeating unit in the polymer structure.

In paragraph 26 of the same document, it is stated:

The Working Group, as asked, discussed criteria.

(1) Concerning MW: the range of 1,000 - 10,000 Mn was agreed as a range within which the concern value was likely to lie.

(2) Concerning MW of low MW compounds giving rise to concern: the agreement was MW below 1,000.

(3) Concerning percentage of low MW compounds of concern: no agreement

(4) Concerning functional groups: only one value, applicable to epoxy and anhydride groups was mentioned (it was 1 reactive group in 20 monomer units); no general conclusion was reached.

(5) Metal content: no value agreed.

(6) Extractivity in water: 10mg/l was seen as acceptable, provided that test conditions were standardized

(7) Cationic charge density: the 5,000 equivalent weight value was accepted (as defined by EPA: not more than one cationic charge in 5000 monomer units).