[reaction: see text] Polyethylene powders with useful loadings of functional groups are accessible by hyperbranched grafting chemistry. Using a 200 microm diameter high-density powder, loadings of up to 0.4 mmol/g of CO(2)H groups are attained. The carboxylic acid groups in the resulting powders can be further functionalized covalently or ionically and resulting powders have the physical durability and solvent resistance associated with polyethylene itself.