Cationic polymerization of isobutylene by AlCl3/ether complexes in non-polar solvents: Effect of ether structure on the selectivity of β-H elimination

• Published in: Polymer (Guilford) Vol. 54; no. 9; pp. 2235 - 2242
• Main Authors: Shiman, Dmitriy I., Vasilenko, Irina V., Kostjuk, Sergei V.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 19.04.2013; Elsevier
• Subjects: Applied sciences; Cationic polymerization; ethers; Exact sciences and technology; Highly reactive polyisobutylene; Isobutylene; molecular weight; Organic polymers; Physicochemistry of polymers; Polymerization; polymers; Preparation, kinetics, thermodynamics, mechanism and catalysts; solvents; temperature; toluene; Highly reactive polyisobutylene; Isobutylene; Cationic polymerization; Lewis acid; Ether; End group; Molecular structure; Priming activity; Experimental study; Solution polymerization; Structure processing relationship; Isobutene polymer; Apolar solvent; Reaction mechanism; Aluminium chloride; Secondary alcohol; Cationic catalyst
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2013.02.039

The cationic polymerization of isobutylene co-initiated by a number of complexes of AlCl3 with linear (Et2O, Bu2O, Am2O, Hex2O, MeOPh) and branched (iPr2O, tBuOMe) ethers in toluene or CH2Cl2 at −20 °C has been investigated. Among them, the complexes with ethers of moderate basicity (AlCl3 × OBu2 and AlCl3 × OiPr2) afforded polyisobutylenes with the highest exo-olefin terminal groups content (80–95%) and monomer conversion, while the use of such weak ether as anisole led to the conventional polyisobutylenes containing mainly tri- and tetra-substituted olefinic end groups (90–95%). The complexes of AlCl3 with tert-butyl methyl ether or tetrahydrofuran are characterized by low stability at room temperature due to the ether cleavage by such strong Lewis acid as AlCl3. The polymerization of isobutylene in the presence of AlCl3 × OBu2 or AlCl3 × OiPr2 as co-initiators could be successfully performed in n-hexane at elevated temperatures (−20 °C to 10 °C) and at high monomer concentrations (up to [M] = 7.8 M) to afford low molecular weight polyisobutylenes (Mn = 1000–8000 g mol−1) with relatively broad MWD (Mw/Mn = 2–4) containing high amount of exo-olefin terminal groups (exo = 70–85%). [Display omitted]