Polychloromethylstyrene (PCMS)-block-polystyrene (PS) copolymers were prepared by controlled free-radical polymerization in the presence of 2,2,6,6-tetramethylpiperidinooxy and 2,2'-azobisisobutyronitrile (AIBN) initiator. The PCMS-b-PS copolymers had narrow molecular weight distributions, and the block lengths were controlled by the reaction time and the molar ratios of chloromethylstyrene/AIBN and styrene/PCMS macroinitiator. The block copolymers were further quaternized with triethylamine. The amphiphilic cationic block copolymers formed colloidal particles; the effects of the pH value, salt concentration, and solvent polarity on the particle size were investigated with a dynamic light scattering analyzer. The average colloid size increased with increasing pH value and salt concentration. This implied that the colloid formed a protonated hydrophilic shell and hydrophobic styrene core in water. Furthermore, with the addition of tetrahydrofuran to the aqueous solution, the styrene segments in the core could be inverted to the outside of the colloid. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128: 239-247, 2013