Summary The cationic polymerization of isobutylene using AlCl3 × OBu2 and AlCl3 × OiPr2 as co‐initiators in two non‐polar solvents (toluene and n‐hexane) at different temperatures and monomer concentrations has been investigated. In toluene, highly reactive polyisobutylene (HR PIB) with desired low molecular weight (Mn = 1,500–2,500 g mol−1) and high exo‐olefin content (85–90%) were synthesized at high monomer concentration ([M] = 5.2–7.8 M) and high reaction temperature (0 °C–20 °C) with both of catalytic complexes. In n‐hexane, AlCl3 × OiPr2 showed considerably higher activity and selectivity towards β‐H abstraction that AlCl3 × OBu2 and allowed to synthesize HR PIB with high functionality (exo ≥ 80%) only at –20 °C, but the molecular weight of synthesized PIB is slightly higher (Mn = 3,500–10,000 g mol−1) than required for the commercial application.

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The activated anionic ring-opening polymerization of e-caprolactam initiated by 0.35 mol% of combined initiator, i.e., equimolar mixture of magnesium di(e-caprolactamate) (CL 2 Mg) with magnesium halides (MgCl 2 , MgBr 2 , and MgI 2 ) as well as of e-caprolactam magnesium bromide (CLMgBr) in the presence of 0.35 mol% of N-acetyl-e-caprolactam as an activator has been investigated in the temperature range 140-200°C. It was found that the reaction rate increased while the apparent activation energy decreased in the following series: CL 2 Mg/ MgCl 2 \ CL 2 Mg/MgBr 2 * CLMgBr \ CL 2 Mg/MgI 2 . In addition, the poly(ecaprolactam)s prepared with CL 2 Mg/MgX 2 (MgX 2 = MgCl 2 , MgBr 2 , and MgI 2 ) are characterized by slightly higher thermal stability than polymers obtained with CLMgBr as initiator. These observations were explained in terms of the coordination of Lewis acids (MgX 2 , where X = Cl, Br, and I) with imide carbonyl of N-acyllactam end groups leading to the increase of their reactivity and stability.

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