Alkyl chloride-boron trichloride initiated polymerizations of isobutylene: Detailed analysis of the initial propagation steps

Living oligomerizations of isobutylene initiated either by cumyl chloride, the [1:1]-adduct of cumyl chloride to isobutylene (P1), the [1:2]-adduct of cumyl chloride to isobutylene (P2), diisobutylene hydrochloride (P1'), or triisobutylene hydrochloride (P2') have been studied in presence of BCl3 and benzyltriethylammonium tetrachloroborate. In contrast to common opinion, the gross propagation rates of the various telechelics depended significantly on the degree of polymerization with k(rel) = 0.07, 1.8, 2.3, 1.3, 1.1, 1.0, 1.0 for Ph-C(CH3)(2)-[CH2-C(CH3)(2)](n)-Cl with n = 1, 2, 3, 4, 5, 6, 7, respectively. These results are compared with the initiation efficiencies of (CH3)(3)C-(CH2-C(CH3)(2)](n)-Cl (k(rel) = 0.3 and 0.8 for n = 1 and 2, respectively). The consequences for the synthesis of telechelics with very narrow molecular weight distribution are discussed.