Polyacrylic acid, starch grafted

Superabsorbent polymers are now commonly made from the polymerization of acrylic acid blended with sodium hydroxide in the presence of an initiator to form a polyacrylic acid, sodium salt (sometimes referred to as cross-linked sodium polyacrylate). Some of the polymers include polyacrylamide copolymer, ethylene maleic anhydride copolymer, cross-linked carboxy-methyl-cellulose, polyvinyl alcohol copolymers, cross-linked polyethylene oxide, and starch grafted copolymer of polyacrylonitrile to name a few. The latter is one of the oldest SAP forms created. 

J.R. Witonoa, I.W. Noordergraaf, H.J. Heeres, L.P.B.M. Janssen, Water absorption, retention and the swelling characteristics of cassava starch grafted with polyacrylic acid, Carbohydr Polym 103 (2014) 325-332. 

The synthetic polyacrylates derived from acrylic acid, and the graft copolymers from starch and acrylic acid have emerged as the absorbent polymers of choice. This is in no small part due to economic factors, as a glance at any chemical marketing periodical will show acrylic acid as one of the least expensive water soluble monomers. In addition, the properties of acrylic acid make it relatively easy to polymerize, and to polymerize to products of high molecular weight. The importance of these latter properties will become clear in the next section. 

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