Synthesis of highly reactive polyisobutylenes with exo-olefin terminals via controlled cationic polymerization with H₂O/FeCl₃/iPrOH initiating system in nonpolar hydrocarbon media

Abstract

Cationic polymerizations of isobutylene (IB) with H 2 O/FeCl 3 /isopropanol (iPrOH) initiating system were conducted in nonpolar hydrocarbon media, such as n-hexane or mixed C 4 fractions at 240 to 20C. This cationic polymerization is a chain-transfer dominated process via highly selective bproton elimination from ACH 3 in the growing chain ends, leading to formation of highly reactive polyisobutylenes (HRPIBs) with large contents (> 90 mol %) of exo-olefin end groups (structure A). The content of structure A remained nearly constant at about 97 mol % during polymerization and isomerization via carbenium ion rearrangement could be suppressed in nonpolar media. First-order kinetics with respect to monomer concentration was measured for selective cationic polymerization of IB in the mixed C 4 fraction feed at 230 C and the apparent rate constant for propagation was 0.028 min 21 .High polymerization temperature (T p ) or [FeCl 3 ] accelerate b-proton elimination or isomerizations and simultaneously decrease selectivity of b-proton abstraction from ACH 3 . Molecular weight decreased and molecular weight distribution (MWD) became narrow with increasing T p or [FeCl 3 ]. To the best of our knowledge, this is the first example to achieve high quality HRPIBs with near 100% of exo-olefin terminals and relatively narrow MWD (M w /M n 5 1.8) by a single-step process in nonpolar hydrocarbon media. PIBs with >70 mol % of exo-olefin end groups (ACH 2 AC(CH 3 )@CH 2 , structure A), preferably more than 80 mol %, are normally referred to as highly reactive polyisobutylenes (HRPIBs). HRPIBs, differing from those conventional PIBs with <10% of exo-olefin end groups, have found applications as intermediates in the preparation of additives for fuels and lubricants or other further functional modification since only terminal exo-olefin in PIB chain has a sufficiently high reactivity.3,4 HRPIBs can efficiently react with maleic anhydride by direct addition reaction to synthesize PIB/maleic anhydride adducts. The high content of exo-olefin end groups and relatively narrow molecular weight distributions (MWDs) are the most important quality criteria for HRPIBs.

Cationic polymerization of isobutylene by complexes of alkylaluminum dichlorides with diisopropyl ether: An activating effect of water

“…However, in n ‐hexane AlCl 3 × OR 2 ‐based initiating systems displayed relatively low activity in the cationic polymerization of IB (40–60% in 30 min in the best conditions), although acceptable functionality (exo content = 75–85%) can be obtained at low reaction temperatures (−20 °C) . The using of H 2 O/FeCl 3 / i PrOH initiating system for the IB polymerization in n ‐hexane proposed recently by Wu and coworkers allowed improving the functionality (exo content above 90%), but the polymerization was relatively slow (70% of monomer conversion in 30 min) and the exo‐olefin end groups content decreased from ∼90% to 83% by the enhancement of reaction temperature from −20 °C to 20 °C. In addition, this initiation system, similarly to AlCl 3 × OR 2 ‐based initiating systems, afforded HR PIB with higher molecular weight ( M n = 3000–10,000 g mol −1 ) than required for the application for motor oil/fuel additives .…”

“…The third approach is based on using of conventional modified Lewis acids in the cationic polymerization of IB (both under heterogeneous and homogeneous conditions) that allowed synthesizing HR PIB in a cost‐effective way and, therefore, this approach is very attractive to industry. Among different catalytic systems including tert ‐butyl chloride/EtZnCl 2 reported by Bochmann and coworkers, the complexes of conventional metal chlorides (MCl 3 , M = Al, Fe, Ga) with ethers attract much attention due to their low cost and high efficiency in the synthesis of HR PIB. It should be noted that complexes of AlCl 3 with ethers, alcohols, and other electron donors were first investigated in the polymerization of IB in the late 1950s‐middle of 1960s .…”

Tailoring the AlCl3/iPr2O/Et2O initiation system for highly reactive polyisobutylene synthesis in pure n-hexane

“…10,12 However, BF 3 is costly and strongly corrosive, resulting in serious economic and safety concerns. 13 In a series of publications, novel and economic catalyst systems were reported to produce HRPIBs with high exo-olen content, 14 such as FeCl 3 /iPrOH, 8,15 FeCl 3 /iPr 2 O, 7,[16][17][18] and AlCl 3 / ether. Among the various coinitiators, solid AlCl 3 has the advantages of low cost and high activity; however, it is always accompanied by the use of chlorinated solvents like CH 2 Cl 2 , 9,[19][20][21][22][23][24][25][26] at least in the preparation of initiator solution.…”

Synthesis of comb‐like dispersants and a study on the effect of dispersant architecture and carbon black dispersion

“…The current method for the synthesis of PIBSI dispersants starts with the preparation of PIB with olefinic end groups through the acid‐catalyzed (AlCl 3 , BF 3 , and BF 3 complexes) polymerization of isobutylene (IB) . Development of new catalysts and catalyst complexes and more cost‐effective processes for the production of highly reactive (HR) PIB are currently active areas of research . Formation of PIB succinic anhydride (PIBSA) is accomplished by reaction of olefin‐terminated PIB with maleic anhydride (MAH), which occurs by either a chlorine‐mediated Diels–Alder reaction (traditional PIB derived from AlCl 3 catalyst) or a thermal ene reaction at temperatures greater than 200 °C (HR PIB derived from BF 3 catalyst) .…”