The functionalization of anionically polymerized isoprene with cysteamine applying the thiol-ene reaction is reported. Antimicrobial activity is implemented by quaternization of the amino functionality by either alkylation or by protonation. The resulting polymers were tested against Gram-positive as well as Gram-negative bacteria strains according to the Japanese Industrial Standard Z2801:2000 protocol, partly revealing excellent biocidal performance. Thermal stability up to 200 degrees C allows extrusion processing of the functionalized poly(isoprene)s. The best performing polymer, that is, bearing butylated ammonium-groups, was compounded with the commodity material poly(propylene). The compound bearing 5 wt % of the biocidal polymer exhibited satisfactory biocidal properties. (C) 2012 Wiley Periodicals, Inc. J PolymSci Part A: Polym Chem 50: 2236-2243, 2012