The zwitterionic carboxybetaines, (3-methacryloylamino-propyl)-(2-carboxy-ethyl)-dimethyl-ammonium (CBMAA-3) and (3-acryloylamino-propyl)-(2-carboxy-ethyl)-dimethyl-ammonium (CBAA-3), were successfully grafted from a galactoglucomannan macroinitiator. The macroinitiator was prepared from the hemicellulose acetylated galactoglucomannan functionalised with α-bromoisobutyric acid. The polymerisation of the betaines was efficiently carried out by a Cu(0) wire catalysed single electron-transfer living radical polymerisation (SET-LRP) in aqueous solution yielding water-soluble graft copolymers and nearly pseudo-first order kinetics suggesting a good degree of control over the polymerisation process. The graft copolymers spontaneously self-assembled in aqueous solution into well-defined nanoparticles highly stable in aqueous media.