Effect of Monomer Loading and Pressure on Particle Formation in Nitroxide-Mediated Precipitation Polymerization in Supercritical Carbon Dioxide

Abstract

The critical degree of polymerization (Jcrit) 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 °C and tert-butyl acrylate (t-BA) at 118 °C in supercritical carbon dioxide (scCO2) mediated by N-tert-butyl-N-[1-diethylphosphono(2,2-dimethylpropyl)]oxy (SG1). The value of Jcrit increases with increasing target molecular weight, initial monomer loading, and pressure. Under the conditions investigated, Jcrit for t-BA is higher than that for St, which is consistent with greater solubility of poly(acrylates) in neat scCO2. A simple graphical approach has been developed and successfully employed, whereby Jcrit can be predicted as a function of both target molecular weight and initial monomer loading on the basis of a data set of Jcrit versus initial monomer loading.