Two monomers with complimentary ultraviolet absorbing moieties, 2-[3-(2H-benzotriazol-2-yl)-4hydroxyphenyl]ethyl methacrylate (BEM) and 2-hydroxy-4-acryloyloxybenzo phenone (HAB), were copolymerized through admicellar polymerization on a cotton fabric surface in order to improve its ultraviolet protection with broad spectral coverage. Separate and combined adsolubilization of the two monomers in dodecylbenzenesulfonate admicelles were studied and compared. Copolymer composition and monomer reactivity ratio were investigated by FTIR using Fineman-Ross and Kelen-Tudos methods and it was found that the BEM-HAB copolymer system showed an alternating tendency and exhibited azeotropic polymerization at a particular composition. The copolymerization method used in this study provided a cotton fabric with uniform and complete UV-protection in the most hazardous regions. Ultraviolet protection factor (UPF) of the modified cotton was studied with a range of copolymer compositions and it was found that the fabrics coated by copolymer had higher values of UPF than homopolymers, while the monomer ratio of 1 : 1 gave the highest UPF value. (C) 2008 Wiley Periodicals, Inc.