TECHNOLOGY FOCUS - POLYMERS - Preferred Synthetic Polymer: The polymer is a vinyl, or diethylenic polymer, a polyurethane or a silicone.Preferred Substituents: Substituents are sulfonated groups and aspartic acid or a derivative, more preferably an ester. The substituents are most preferably linked to the polymer by a sulfamide bond.Preferred Copolymer: The copolymer comprises 4-50, (preferably 25-31, most preferably 29) mol.% of unsubstituted styrene units, 15-51 (preferably 21-25, most preferably 24) mol.% of styrene units substituted with sulfonate groups and 44-55 (most preferably 47) mol.% of styrene units substituted with dimethyl esters of aspartic acid linked by a sulfonamide bond. EXAMPLE - BioBeads SX3 (RTM: polystyrene microspheres crosslinked with DVB) were freed of residual impurities. Substituents were sulfamides of the methyl esters of aspartic acid, phenylalanine, leucine and alanine. Chlorosulfonation was carried out by swelling microspheres (2.5 g) in 75ml trichloroethane and contacting them with an excess of chlorosulfonic acid for 60 minutes at 40 degreesC with reflux and then rinsing under vacuum with distilled dichloromethane, distilled acetone and dichloromethane and then dispersed in 100 ml of dichloromethane. Sulfamidation to about 10% was carried out using 0.11 mol of leucine, phenylalanine, or mono- or dimethyl ester hydrochlorate per mol of dry polystyrene. The reaction was initiated with 2 mol equiv. of triethylamine (0.73ml) followed by gentle agitation of the mixture for 48 hours. Further diethylamine (0.36ml) was then added and the reaction medium stirred for 12 hours. The polymers were then filtered and rinsed for three hours in ethanol. The aspartic acid and alanine substituted copolymers were then subjected to weak hydrolysis with six washes with 10power-2 M NaOH and rinsed with water to a constant pH. The phenylalanine and leucine substituted copolymers were subjected to strong hydrolysis using 2M NaOH with an increasing and then decreasing concentration to avoid damage to the microspheres. The final polymers had in, unit%, styrene 27/21/26/32, sulfonate 64/73/66/60, aminated acid 9/6/8/8 and degree of swelling 150/210/150/215.