NEARCRITICAL AND SUPERCRITICAL FLUID SOLVENTS FOR LIVING ANIONIC POLYMERIZATIONS

Near- and supercritical fluids are investigated as solvents for anioni c polymerizations of 1,3-dienes. Solvent strength (solubility paramete r) of mixtures of light hydrocarbons containing cyclohexane is shown t o be adjustable using solvatochromic probe methods. The results indica te that these mixtures have solubility parameter values that are lower than conventional liquid solvents and represent a regime of solvent s trength that has remained unexplored for ionic polymerizations. The an ionic 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/cyclohex ane mixtures.