A cationic macromonomer, 2-methacryloylethylhexadecyldimethylammonium bromide MA16, and a cationic macroinitiator, cationic acrylic/styrene oligomer end-capped with a nitroxide, were used to modify pristine Na-MMT, to enhance compatibility between the clay platelets and the host acrylic polymer matrix in waterborne nanocomposites. Both cationic species were successfully exchanged in the montmorillonite. The organically modified clays were used for the synthesis of acrylic (MMA/BA)/clay waterborne nanocomposites by miniemulsion polymerization. The 30% solids containing latexes were stable and coagulum free and presented better mechanical, thermal and barrier properties than the pristine acrylic copolymer.