NEARCRITICAL AND SUPERCRITICAL FLUID SOLVENTS FOR LIVING ANIONIC POLYMERIZATIONS

Near- and supercritical fluids are investigated as solvents for anionic polymerizations of 1,3-dienes. Solvent strength (solubility parameter) of mixtures of light hydrocarbons containing cyclohexane is shown to be adjustable using solvatochromic probe methods. The results indicate that these mixtures have solubility parameter values that are lower than conventional liquid solvents and represent a regime of solvent strength that has remained unexplored for ionic polymerizations. The anionic initiator 3-methyl-1,1-diphenyl-pentyllithium (MDPPL) was shown to be soluble in supercritical ethane and that its ultraviolet/visible absorption maximum was sensitive to systematic density changes of the supercritical fluid induced by pressure profiling. These results were extended to the anionic polymerization ot isoprene in butane/cyclohexane mixtures.