Polymerization of isobutylene catalyzed by EtAlCl₂/bis(2-chloroethyl) ether complex in steel vessels

Abstract

When synthesis of highly reactive polyisobutylene (HR PIB) via cationic polymerization of isobutylene (IB) using ethylaluminum dichloride·bis(2-chloroethyl) ether (EADC·CEE) complex were carried out in metal reactors made of 316 stainless steel (SS), PIB olefin with up to 20% lower exo-olefin content were obtained compared to that obtained in glass reactors (up to 90%). In an effort to investigate this reduction in exo-olefin selectivity in SS reactors, we have studied the polymerization of IB using EADC·CEE complex in SS (minimum of 10.5% chromium content by mass), carbon steel (CS) (0% chromium content by mass), monel alloy 400 (M400) (0% chromium content by mass) and glass reactors. The latter was examined in the presence and absence of SS balls. Mechanistic studies using ATR-FTIR and 1 H NMR spectroscopy suggest that this decrease in exo-olefin selectivity is due to a side reaction of EADC with Cr 2 O 3 involving the loss of the ethyl group from EADC and decomplexation of the EADC·CEE complex which hinders the selective abstraction of the β-proton from the growing chain end. In the absence of chromium (CS and M400 reactors), the exo-olefin content is virtually identical to that obtained in glass reactors. Therefore, CS and M400 reactors are suitable to produce HR PIB with high exo-olefin content.

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

“…Catalytic chain transfer polymerization (CCTP) in nonpolar solvents at moderate temperatures has developed into one of the most adaptable polymerization techniques for the synthesis of highly reactive polyisobutylene (HRPIB) in recent years. − Low molecular weight HRPIB ( M n = 500–5000 g/mol) is a valuable precursor in the preparation of motor oil and fuel auxiliaries. − Initially, metal halide (AlCl 3 , GaCl 3 , FeCl 3 , etc.) ether complexes (MX n ·ether) were shown to be better catalysts for the synthesis of HRPIB at moderate temperatures compared to traditional catalysts. − However, their application in nonpolar solvents is limited because of poor solubility, which affects the polymerization rate. − This issue was lately overcome by employing alkylaluminum dichloride ether complexes as hydrocarbon soluble catalysts. − We have shown that the ethylaluminum dichloride (EADC)·bis­(2-chloroethyl) ether (CEE) complex is an effective catalyst, which not only polymerizes pure IB feed but also polymerizes mixed C4 olefin feeds at 0–10 °C to yield up to 88% exo-olefin content . In these studies, polymerization conditions and products have been optimized for a batch reactor.…”

“…With decreasing temperature, molecular weights could be increased, , but at the expense of polymerization rate. Decreasing the [CEE]/[EADC] ratios from 1.5 to 1, the molecular weight increases but the exo content drops (from 90 to 70%). − …”

Cationic Copolymerization and Multicomponent Polymerization of Isobutylene with C4 Olefins

“…Thus, in the past few years several new catalyst systems have been developed to synthesize HRPIB. − Among the various approaches, high percentage (up to 90%) of exo-olefin content could be achieved in either dehydrochlorination of tert -chlorine-terminated PIB (PIBCl) or quenching the living PIB cations with dialkyl ether/base, dialkyl (or) diaryl sulfide/base, or hindered bases. ,, Solvent-ligated [M­(NCMe) 6 ] 2+ (M II = Mn, Cu, Mo, Fe, or Zn) complexes with weakly coordinating borate or aluminate anions were also established as an effective initiating systems to prepare HRPIB with high exo-olefin functionality . Very recently, Lewis acid (LA) and Lewis base (LB) complexes were reported for the catalytic chain transfer polymerization of IB, and several research groups have made significant contributions to develop effective LA·LB initiating systems to prepare HRPIB. ,,, In our earlier attempts, we developed MCl 3 ·ether complexes (M = Al, Ga, and Fe) to obtain high exo-functionality (up to 85%) at −20 to +10 °C. − We also developed an effective co-initiating system by using ethylaluminum dichloride (EADC)·bis­(2-chloroethyl) ether (CEE) complex, which works efficiently in hexanes (nonpolar solvent) at −20 to 20 °C to reach more than 90% exo-olefin content. ,− …”

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

“…Supporting Information Figure S1 shows a typical 1 H NMR spectrum of a representative HR PIB sample prepared in this study. The M n s ( M n,NMR ) of the HR PIB samples were calculated by the 1 H NMR integrals of end‐groups and backbone‐related peaks of the polymer as described previously …”