Vinylidene fluoride was polymerised in supercritical carbon dioxide. Power compensation calorimetry was used to monitor the polymerisation process on-line. The polymer product was found to have a low apparent-density, leading to an observed high solid content in the autoclave at low yields. In situ calorimetry showed a sharp transition of the heat transfer in the reactor, leading to a useful parameter for monitoring the polymerisation process. The stirring rate was found to have no effect on the molecular weight, but did modify the calorimetric traces and the morphology of the polymer. The polymerisation at a lower pressure resulted in a lower molecular weight product and a lower polymerisation rate. (C) 2004 Elsevier Ltd. All rights reserved.