Understanding the Kinetics of the Atom Transfer Radical Polymerization of Vinyl Acetate in Bulk and Solution in Supercritical Carbon Dioxide

Polymerizations in supercritical carbon dioxide (scCO2) offer an ecofriendly and efficient method for polymer synthesis and processing. Most radical polymerizations carried out in scCO2 will initially proceed as homogeneous polymerization until in situ generated high molar mass macromolecules phase separate. However, when the monomer concentration, acting as a cosolvent, is sufficiently high, macromolecular solubility is enhanced, allowing the reaction to proceed as a single-phase system even at high monomer conversion levels. This study analyzes previously reported kinetic data on the bulk atom transfer radical polymerization (ATRP) of vinyl acetate/ethyl-2-bromoisobutyrate/CuBr/2,2′:6′,2′-terpyridine at 70 °C and 1 bar, as well as solution ATRP in CO2 at 60–70 °C and 310 bar. The perturbed-chain statistical associating fluid theory equation of state is used to estimate the solubility of the macromolecules in the reaction mixture in the case of ATRP in scCO2. The model predicts that poly(vinyl acetate) remains completely soluble in CO2 throughout the reaction and the number-average chain-length increases linearly with monomer conversion for all nine case studies considered.