Latex fractionation by sedimentation and colloidal crystallization: The case of poly(styrene-co-acrylamide)

Poly(styrene-co-acrylamide) (PS-AAM) latex was prepared, fractionated by se dimentation under gravity, and characterized by PCS, infrared spectra, seco ndary and backscattered electron imaging in the scanning electron microscop e, and electron spectroscopy imaging in an analytical transmission electron microscope. Three latex fractions were obtained. The lower fraction was op alescent and its particles were the more uniform, concerning size, chemical composition, and topochemical features. This lower fraction was still furt her fractionated by zonal centrifugation in a density gradient, yielding tw o fractions with similar macrocrystal-forming abilities but different sizes and chemical compositions. These results confirm those previously obtained for the PS-HEMA latex. (C) 2000 Academic Press.