Butyl cyanoacrylate has been polymerised by dispersion in acidified water to yield nanoparticles. Reactions have been carried out at various temperatures and the molecular weight of the growing polymer measured. In all cases polymerisation proceeds by generation of discrete populations of oligomers, which are then re-initiated and undergo further growth. The peak molecular weight is around 1300 g/mol and it is considered that a stepwise initiation, termination and re-initiation process continues until diffusionally limited by the internal viscosity within the nanoparticle.