The amount of water-miscible organic solvents such as acetone or ethanol required to precipitate polysaccharides from water depends significantly on their molecular weight. Many synthetic (as opposed to natural) polysaccharides are of relatively low MW, and will require high concentrations of ethanol or acetone to precipitate. Some may not precipitate at all.  Chilling can help speed things up.  CTAB and other quaternary detergents will precipitate anionic polysaccharides such as polyuronates or sulfated polysaccharides by forming an ionic complex that will precipitate from water. These complexes will redissolve in high concentrations of salts like KCl.  Normally, neutral polysaccharides will not form such ionic complexes and will not precipitate. However, in some cases, you might be able to form a borate complex with the polysaccharide, and then precipitate that complex with CTAB.