| http://www.w3.org/ns/prov#value | - There is also employed a highly water-absorbing polymer described in U.S. Pat. No. 4,960,681 and JP-A 62-245260, including a homopolymer of vinyl monomers containing ???COOM or ???SO3M (in which M is an alkali metal), and copolymers of these monomers or copolymer with other monomer (such as sodium methacrylate, ammonium methacrylate or potassium acrylate).
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