Living Carbocationic Polymerization. XLIX. Two-Stage Living Polymerization of Isobutylene to Di-tert-chlorine Telechelic Polyisobutylene

A two-stage process was developed for the living polymerization of isobutylene (IB) employing di-tert-alcohol initiators in conjunction with BCl3 coinitiator in the first or initiation stage, followed by TiCl4 coinitiator in the second or propagation stage; the process was shown to yield high molecular weight (up to M n 20,000), narrow molecular weight distribution (MWD) M w/M n = 1.1–1.2) di-tert-chlorine telechelic polyisobutylenes (tCl-PIB-Clt). The initiation stage involves the homogeneous solution living polymerization of IB induced by the di-tert-alcohol/BCl3 combination in the presence of an electron donor such as N,N-dimethylacetamide in CH3Cl solvent at −80°C and proceeds up to M n < 5000; this is followed by the propagation stage in which TiCl4 and the bulk of IB plus a sufficient amount of n-C6H14 are added to the charge to bring the solvent composition to CH3Cl/n-C6H14 60/40 v/v and the living polymerization is continued until high M n product is obtained. This two-stage process was developed because 1) it employs very inexpensive chemicals; 2) di-tert-alcohol/BCl3 combinations initiate living IB polymerization in CH3Cl but the product after reaching M n ≤ 5000 precipitates out of the CH3Cl solution, and di-tert-alcohol/BCl4 combinations do not initiate IB polymerization; and 3) di-tert-alcohol/BCl3 systems do not initiate (or only very slowly) the living polymerization of IB in CH3Cl/n-C6H14 mixtures, whereas similar TiCl4-based systems do. The polymerization remains living during both stages although the propagating species and solvent polarity are profoundly altered. The livingness of the system has been analyzed by kinetic experiments and the structure of the tCl-PIB-Clt product by routine spectroscopic means.