Electron Donors as Colorimetric Indicators of Protic Impurity Removal in Living Cationic Polymerization of Isobutylene

Abstract

Various tertiary amines including octyl-p-(dimethylamino)benzoate, N,N-dimethyl-m-toluidine, ethyl-p-(dimethylamino)benzoate, and quinoline were examined as external electron donors in the living cationic polymerization of isobutylene using a 1,3-bis(2-chloro-2-propyl)-5-tert-butylbenzene (t-Bu-m-DCC)/ED/TiCl4 initiating system in hexane/methyl chloride cosolvents. These aromatic amines were observed to retard the rate of polymerization and, when added to the polymerization reaction in excess of the concentration of protic impurities, were observed to form vividly colored complexes with TiCl4. Under these conditions, initiation by protic impurities was suppressed, and the polymerizations were living as demonstrated by linearity of first-order kinetic and M n vs conversion plots, and absence of unsaturation at the polyisobutylene chain ends. When the concentration of amine was below that of protic impurities, the polymerizations were colorless and nonliving; thus these amines yield a colorimetric indication of protic impurity elimination. GPC chromatograms also demonstrated that the elimination of initiation by protic impurities coincided with the color change.