A composition of matter comprising an amphiphilic star polymer, the star polymer comprising a crosslinked microgel core and 6 or more independent polymer arms covalently linked to the core, the 6 or more arms each comprising a hydrophilic polymer chain segment and a hydrophobic polymer chain segment; wherein each individual metal selected from the group consisting of beryllium, magnesium, calcium, strontium, barium, radium, aluminum, gallium, indium, thallium, germanium, tin, lead, arsenic, antimony, bismuth, tellurium, polonium, and metals of Groups 3 to 12 of the Periodic Table has a concentration in the star polymer of greater than or equal to 0 parts per million and less than or equal to 100 parts per million.