The critical degree of polymerization at which polymer chains become insoluble in the continuous medium and particle formation commences has been estimated Under a variety of experimental conditions for the nitroxide-mediated precipitation polymerizations of styrene (St) at 110 degrees C and tert-butyl acrylate (t-BA) at 118 degrees C in supercritical carbon dioxide (scCO(2)) mediated by N-tert-butyl-N-[1-diethyl-phosphono(2,2-dimethylpropyl)]oxy (SG1). The value of J(crit) increases with increasing target molecular weight, initial monomer loading and pressure. Under the conditions investigated, J(crit) for t-BA is higher than that for St, which is consistent with greater solubility of poly(acrylates) in neat scCO(2). A simple graphical approach has been developed and successfully employed, whereby J(crit) can be predicted as a function of both target molecular weight and initial monomer loading on the basis of a data set of J(crit) versus initial monomer loading.