A dispersant comprising a polyester chain obtainable by polymerising a hydroxy carboxylic acid or lactone thereof such as E-caprolactone with a cyclic alkylene carbonate such as 5,5-dimethyltrimethylene carbonate. The dispersant may be in the form of a phosphate ester where the polyester chain is reacted with a phosphating agent such as polyphosphoric acid or the polyester chain may be attached to a polyamine or polyimine such as polyethyleneimine.