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

Abstract

Fast polymerization of isobutylene (IB) initiated by tert‐butyl chloride using ethylaluminum dichloride·bis(2‐chloroethyl) ether complex (T. Rajasekhar, J. Emert, R. Faust, Polym. Chem. 2017, 8, 2852) was drastically slowed down in the presence of impurities, such as propionic acid, acetone, methanol, and acetonitrile. The effect of impurities on the polymerization rate was neutralized by using two different approaches. First, addition of a small amount of iron trichloride (FeCl3) scavenged the impurity and formed an insoluble FeCl3··impurity complex in hexanes. The polymerization rate and exo‐olefin content were virtually identical to that obtained in the absence of impurities. Heterogeneous phase scavenger (FeCl3) exhibited better performance than homogenous phase scavengers. In the second approach, conducting the polymerization in wet hexanes, the fast polymerization of IB was retained in the presence of impurities with a slight decrease in exo‐olefin content. 1H NMR studies suggest that nucleophilic impurities are protonated in the presence of water, and thereby neutralized. Mechanistic studies suggest that the rate constant of activation (ka), rate constant of propagation (kp), and rate constant of β‐proton elimination (ktr) are not affected by the presence of impurities. To account for the retardation of polymerization in the presence of impurities, delay of proton transfer to monomer in the chain transfer step is proposed. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3697–3704

Controlled Catalytic Chain Transfer Polymerization of Isobutylene in the Presence of tert-Butanol as Exo-Enhancer

“…We recently studied the role of various organic nucleophilic impurities such as propionic acid, acetone, methanol, and acetonitrile in CCTP. Interestingly, it was found that exo-olefin content slightly increased in the presence of ppm levels of methanol while molecular weights remained virtually identical to that obtained in the absence of methanol with [CEE]:[EADC] = 1 . There are few reports about controlled cationic polymerization for HRPIB synthesis in the presence of alcohols, − and the reason for the exo content increase is still unclear.…”

“…There are few reports about controlled cationic polymerization for HRPIB synthesis in the presence of alcohols, − and the reason for the exo content increase is still unclear. Moreover, relatively strong nucleophiles inactivate the polymerization or decrease the concentration of active species. ,− In this report, we present a detailed investigation on the mechanistic role of alcohol in EADC·CEE catalyzed chain transfer polymerization of IB as well as discuss the effectiveness of tertiary alcohols compared to secondary and primary alcohols (Scheme ).…”

“…Interestingly, it was found that exo-olefin content slightly increased in the presence of ppm levels of methanol while molecular weights remained virtually identical to that obtained in the absence of methanol with [CEE]: [EADC] = 1. 30 There are few reports about controlled cationic polymerization for HRPIB synthesis in the presence of alcohols, 31−34 and the reason for the exo content increase is still unclear. Moreover, relatively strong nucleophiles inactivate the polymerization or decrease the concentration of active species.…”

Homogeneous and heterogeneous catalysts for the synthesis of highly reactive polyisobutylene: discovery, development and perspectives

“…[37] Another interesting feature of t BuCl/EtAlCl 2 ÂCEE initiating system in the synthesis of HR PIB is the significant retardation of the reaction in the presence of nucleophilic impurities such as acetone, methanol, propionic acid or acetonitrile. [38] It was shown that interaction of protons with these impurities results in delay of proton transfer to monomer in the chain transfer to monomer step (see Scheme 5) leading to observed retardation of the polymerization. The negative effect of the nucleophilic impurities could be neutralized either by the addition of FeCl 3 or H 2 O (using wet hexane as reaction medium).…”

“…The negative effect of the nucleophilic impurities could be neutralized either by the addition of FeCl 3 or H 2 O (using wet hexane as reaction medium). [38] It should be also noted that t BuCl/EtAlCl 2 ÂCEE initiating system, similarly to H 2 O/ i BuAlCl 2 /O i Pr 2 system, [33] could be used for the synthesis of HR PIB from C 4 mixed olefin feed. [39] In addition, this initiating system also displayed improved efficiency toward synthesis of HR PIB under micromixing conditions.…”