NOVELTY - A polystyrene sulfonate copolymer contains styrene sulfonic-acid monomer residue having sulfonate-containing structural unit (I) and N-substituted maleimide residue having carbonyl group-containing structural unit (II) and other vinyl monomer residue having hydrocarbon-containing structural unit (III) copolymerizable with styrene sulfonic-acid monomer residue and N-substituted maleimide residue. The N-substituted maleimide monomer residue is monomer residue of compound chosen from N-phenyl maleimide, N-carboxyphenyl maleimide and N-naphthyl maleimide.    USE - Polystyrene sulfonate copolymer is used for dispersing agent, carbon-nanotube aqueous dispersion, graphene aqueous dispersion and fullerene aqueous dispersion (all claimed). Uses include but are not limited to micromachine, carbon-dioxide fixing material, hydrogen gas-occlusion material, electromagnetic wave-shielding material, catalyst support material, nanofilter, biosensor, drug delivery system, fuel cell, secondary battery and field-emission display.    ADVANTAGE - The polystyrene sulfonate copolymer is manufactured, by simple method. The product containing the polystyrene sulfonate copolymer has excellent strength.    DETAILED DESCRIPTION - A polystyrene sulfonate copolymer contains (in mol%) styrene sulfonic-acid monomer residue (95-30) having sulfonate-containing structural unit of formula (I) and N-substituted maleimide residue (5-70) having carbonyl group-containing structural unit of formula (II) and other vinyl monomer residue (0-20) having hydrocarbon-containing structural unit of formula: -(C(-R2)(-R4)-C(-R3)(-R5))- (III) copolymerizable with styrene sulfonic-acid monomer residue and N-substituted maleimide residue. The N-substituted maleimide monomer residue is monomer residue of compound chosen from N-phenyl maleimide, N-chlorophenylmaleimide, N-methyl phenylmaleimide, N-carboxyphenyl maleimide and N-naphthyl maleimide. The sum of content of styrene sulfonic-acid monomer residue, N-substituted maleimide residue and other vinyl monomer residue is 100 mol%.    X+=sodium cation, lithium cation, potassium cation, ammonium cation, quaternary ammonium cation or proton;    R1=optionally substituted aryl;and    R2-R5=ester, cyano, carboxy, H, or aliphatic hydrocarbyl or aryl (both optionally substituted).    An INDEPENDENT CLAIM is included for manufacture of polystyrene sulfonate copolymer.