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Living carbocationic polymerization XIV. Living polymerization of isobutylene with ester‐TiCl 4 complexes
Author(s) -
Kaszás Gabor,
Puskás Judit,
Kennedy Joseph P.
Publication year - 1988
Publication title -
makromolekulare chemie. macromolecular symposia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.257
H-Index - 76
eISSN - 1521-3900
pISSN - 0258-0322
DOI - 10.1002/masy.19880130134
Subject(s) - isobutylene , propionate , chemistry , polymerization , cationic polymerization , living cationic polymerization , polymer chemistry , living polymerization , solvent , yield (engineering) , organic chemistry , ring opening polymerization , radical polymerization , copolymer , polymer , materials science , metallurgy
The living polymerization of isobutylene (IB) has been induced by cumyl acetate·TiCl 4 and cumyl propionate·TiCl 4 complexes in CH 2 Cl 2 /n‐C 6 H 14 and CH 3 Cl/n‐C 6 H 14 mixtures under conventional laboratory conditions at −40°C. The living nature of the polymerization was demonstrated by linear M̄ n versus W p (g PIB formed) plots starting at the origin. DP n obeys [IB]/[cumyl acetate·TiCl 4 ] and molecular weight distributions (MWD) are very narrow, M̄ w /M̄ n = 1.05–1.13. PIBs having M̄ n >40000 have been prepared. The effects of the nature of the solvent, solvent composition, nature of the ester, ester/TiCl 4 ratio and concentrations on rates, M̄ n s and MWDs have been investigated. The living polymerization is faster by the cumyl acetate‐TiCl 4 than by the cumyl propionate·TiCl 4 complex. The rate of living polymerizations is negligible at CuAc/TiCl 4 = 1 and increases significantly in the presence of stoichiometric excess of TiCl 4 over the ester. Undesirable initiation due to protogenic impurities can be suppressed by employing relatively nonpolar (hexane‐rich) media, by increasing the ester/TiCl 4 , ratio, or by the addition of a non‐initiating ester (ethyl acetate); however, the rates decrease as a consequence of these measures. Polymerizations induced by mixtures of cumyl acetate·TiCl 4 /cumyl propionate·TiCl 4 complexes yield monomodal narrow MWDs indicating rapid ester exchange at the growing site which in turn suggests ionic active species. The kinetic findings are explained by a mechanistic scheme that rests on two propositions: Propagation involves activated (most probably ionized) polymer‐ester·Lewis acid complexes, and free (uncomplexed) Lewis acid causes irreversible destruction of living propagation.