Cationic polymers

Last update 7 April 2017

To be eligible as a PLC, a polymer must have a low charge, or cationic, density.

Cationic polymers and polymers reasonably anticipated to become cationic in a natural aquatic environment are not eligible as PLCs. The main concern is their toxicity towards aquatic organisms such as fish and algae.

For the purposes of the Act, and this guidance, these definitions apply:

  • A polymer is a low charge density polymer if it is:
    • not a cationic polymer or is not reasonably anticipated to become a cationic polymer in a natural aquatic environment (4<pH<9), or
    • a solid material that is not soluble or dispersible in water and will only be used in the solid phase (for example ion exchange beads), or
    • cationic (or potentially cationic) and the combined (total) FGEW of cationic groups is 5000 or above (see: How to calculate functional group equivalent weight).
  • A cationic polymer is a polymer containing a net positively-charged atom/s or associated group/s of atoms covalently linked to its polymer molecule. Examples are the ammonium, phosphonium and sulfonium cations.
  • A potentially cationic polymer is a polymer containing groups reasonably anticipated to become cationic. Examples are all amines (primary, secondary, tertiary, aromatic, etc.) and all isocyanates (which hydrolyse to form carbamic acids, then decarboxylate to form amines).
  • Reasonably anticipated means aknowledgeable person would expect a given physical or chemical composition or characteristic to occur, based on factors such as the nature of the precursors used to manufacture the polymer, the type of reaction, the type of manufacturing process, the products produced in the polymerisation, the intended uses of the substance and associated use conditions.

Example

Consider a polyamide of NAMW 7000 manufactured from equimolar amounts of ethanediamine and isophthalic acid.

On average, the polymer will have one unreacted amino group at one end of the polymer chain and an unreacted carboxylic acid group at the other end. The amino group is potentially cationic so—as FGEW is defined as the ratio of the NAMW to the number of RFGs—the FGEW for the amino group is 7000/1.

Therefore, the polymer meets the criteria for low charge density as the FGEW is above 5000. If the NAMW had been <5000, or if the polymer had two free amine groups, then the polymer would not be eligible as a PLC.