Radical polymerizations from third to fifth generation macromonomers were conducted in supercritical carbon dioxide (scCO(2)). It was found that all monomers were not soluble in such a medium, and reactions occurred in the CO2-swollen monomer matrices. Despite the expected severe diffusion limitations, very high conversions and molecular weights were obtained. It is believed that the plasticization effect induced by the CO2 plays a key role in these surprising findings. Scanning force microscopical analyses confirmed that mainly linear dendronized polymers were obtained and therefore chain transfer to polymer is virtually irrelevant.