Highly reactive polyisobutylenes via AlCl₃OBu₂‐coinitiated cationic polymerization of isobutylene: Effect of solvent polarity, temperature, and initiator

Abstract

The cationic polymerization of isobutylene using 2‐phenyl‐2‐propanol (CumOH)/AlCl3OBu2 and H2O/AlCl3OBu2 initiating systems in nonpolar solvents (toluene, n‐hexane) at elevated temperatures (−20 to 30 °C) is reported. With CumOH/AlCl3OBu2 initiating system, the reaction proceeded by controlled initiation via CumOH, followed by β‐H abstraction and then irreversible termination, thus, affording polymers (Mn = 1000–2000 g mol−1) with high content of vinylidene end groups (85–91%), although the monomer conversion was low (≤35%) and polymers exhibited relatively broad molecular weight distribution (MWD; Mw/Mn = 2.3–3.5). H2O/AlCl3OBu2 initiating system induced chain‐transfer dominated cationic polymerization of isobutylene via a selective β‐H abstraction by free base (Bu2O). Under these conditions, polymers with very high content of desired exo‐olefin terminal groups (89–94%) in high yield (>85%) were obtained in 10 min. It was shown that the molecular weight of polyisobutylenes obtained with H2O/AlCl3OBu2 initiating system could be easily controlled in a range 1000–10,000 g mol−1 by changing the reaction temperature from −40 to 30 °C. The MWD was rather broad (Mw/Mn = 2.5–3.5) at low reaction temperatures (from −40 to 10 °C), but became narrower (Mw/Mn ≤ 2.1) at temperatures higher than 10 °C. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Cationic polymerization of isobutylene at room temperature

“…This approach opens an access to difunctional exo ‐olefin terminated PIB 30. However, because of the partial decomposition of initiator, this initiating system could not be used at high reaction temperatures ( T > 0 °C) 23, 31. Therefore, the simplest initiating system, i.e., adventitious H 2 O/AlCl 3 OR 2 (R = Bu 2 O, i Pr 2 O), was then investigated to conduct the cationic polymerization of IB at high reaction temperatures 23, 25, 31…”

“…One significant drawback of the aforementioned initiating systems is the conducting of the polymerization in toxic chlorinated solvent. To replace CH 2 Cl 2 , the polymerization of IB with H 2 O/AlCl 3 OBu 2 initiating system was studied in different solvents (toluene, α,α,α‐trifluorotoluene, and n ‐hexane) 29, 31, 33. In toluene, the H 2 O/AlCl 3 OBu 2 initiating system afforded low‐molecular‐weight HR PIB ( M n = 1000−2100 g mol −1 ) with relatively narrow MWD ( M w / M n = 1.4−2.6) in a good yield (70−90% in 10 min) and even with a better functionality (90−94% of exo ‐olefin end groups) compared to CH 2 Cl 2 at T > 0 °C (Table 1).…”

“…Besides, the increase of the monomer concentration from [IB] = 0.9 M up to [IB] = 5.2 M almost did not influence the functionality of the obtained polymers ( exo = 86−90%) (Table 1). 31…”

Characteristics and Mechanism of Styrene Cationic Polymerization in Aqueous Media Initiated by Cumyl Alcohol/B(C6F5)3

“…Chlorinated solvents bring a severe burden to the environment, and their use should be avoided . With the development of green chemistry, much attention has been given to the alternative, mild, and environmentally friendly solvents for the cationic polymerization of vinyl monomers, such as ionic liquids, supercritical carbon dioxide, or less‐toxic organic solvents (e.g., n ‐hexane) . Since Sawamoto et al .…”

Catalytic chain transfer polymerization of isobutylene: The role of nucleophilic impurities

“…The exo‐olefin terminated PIB is also referred to as “highly reactive” PIB (HR PIB), since it readily reacts with maleic anhydride in a thermal “ene” reaction to produce PIB succinic anhydride that can be converted to polyisobutenylsuccinimide, used as ashless dispersants. In the recent years, several research groups have reported on new catalyst systems for the synthesis of HR PIB . Some major drawbacks for the new HR PIB process systems include low process temperatures and/or use of polar chlorinated solvents that present serious limitations for industrial application .…”