Polyacrylonitriles prepared by aqueous free-radical slurry polymerization at 40 degrees C using ammonium persulfate and sodium metabisulfite as redox initiator have been examined by FTi.r. and by high-field C-13 and H-1 n.m.r. They have been shown to contain small quantities of acrylamide and acrylic acid units and to possess predominantly sulfonate and non-sulfur containing end-groups derived principally from transfer to bisulfite ion during the polymerization. Other end-groups present in low concentration are sulfate and hydroxyl; the former probably arises from initiation by sulfate radical anions and the latter either from transfer to water or by adventitious hydrolysis of some of the sulfate end-groups. Because they contain few groups capable of initiating intramolecular cyclization, the polyacrylonitriles are white with no sign of discoloration.