In Situ Quenching Methods Toward exo‐Olefin‐Terminated Polyisobutylene

Abstract

Abstractexo‐Olefin‐terminated polyisobutylene was obtained directly from living isobutylene polymerizations by addition of a quenching compound to the living chain ends. Three broad classes of compounds were evaluated including hindered bases such as hindered pyridines and piperidines, N‐hydro‐2,5‐disubstitutedpyrroles, and sulfides, ethers, and silylethers. The proposed mechanism of quenching unique to each class was discussed, with supporting kinetic, spectroscopic, and structure‐based evidence presented. Hindered bases were proposed to operate by E2 elimination reaction of free base at the carbenium ion. N‐Hydro‐2,5‐disubstitutedpyrroles were proposed to form the η5‐2,5‐disubstitutedpyrrolyltrichloro‐titanium(IV) coordination complex, which serves as the true quencher. Sulfides, ethers, and silylethers were proposed to operate by first converting the PIB chain ends quantitatively to the onium adduct, which is then decomposed to form exo‐olefin PIB. Sulfides and ethers were the best performing quenchers of all the types studied, particularly bulky ones such di‐tert‐butylsulfide and diisopropyl ether.

Recent progress in the Lewis acid co-initiated cationic polymerization of isobutylene and 1,3-dienes

“…1) on the formation of exo-olen end group through the end-quenching of TiCl 4 -co-initiated living cationic polymerization of IB. [33][34][35] Among these bases, the highest efficiency showed PMP and TMP which yielded PIB with 100% of exo-olen end groups and can be used at relatively concentrated conditions ([IB] # 1.5 M). 34,35 The low efficiency of DTBP is consistent with its steric hindrance that prevents the efficient b-H abstraction, on the one hand.…”

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 .…”

“…In the recent years, several research groups have reported on new catalyst systems for the synthesis of HR PIB. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] 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. [26][27][28] Recently, we reported an ethylaluminum dichloride (EADC)Ábis(2-chloroethyl) ether (CEE) complex as a fully hydrocarbon soluble catalyst that in conjunction with tert-butyl chloride (t-BuCl) initiator in hexanes at 0-20 8C gave HR PIB with quantitative yields and up to 92% exo-olefin end-functionality.…”

Direct synthesis of highly reactive polyisobutylenes via cationic polymerization of isobutylene co‐initiated with TiCl4 in nonpolar hydrocarbon media

“…HRPIBs synthesis by process (B) could also be conducted via specific termination reaction after completion of living cationic polymerization coinitiated with TiCl 4 by addition of allyltrimethylsilane, strong hindered bases, such as 2,5-disubstituted pyrroles, hindered aliphatic tertiary amines, partially hindered pyridines or sulfides, or modification from tert-chloro-terminated functional PIB chains reaction. [63][64][65][66][67][68][69][70][71][72][73][74][75] The TMPCl/FeCl 3 /iPrOH initiating system has been recently developed in our research group to achieve living cationic polymerization of IB in CH 2 Cl 2 /hexane mixture at 280 C. 19 Very interestingly, the chain-transfer-dominated cationic polymerization of IB with H 2 O/FeCl 3 /iPrOH initiating system in nonpolar hydrocarbons at 240 to 20 C has also been achieved in our research group, leading to direct synthesis of HRPIBs with more than 90 mol % of exo-olefin. 62 It indicates that living cationic polymerization of IB co-initiated by FeCl 3 could be transformed to chain-transfer-dominated process by changing reaction conditions.…”

“…HRPIBs synthesis by process (B) could also be conducted via specific termination reaction after completion of living cationic polymerization coinitiated with TiCl 4 by addition of allyltrimethylsilane, strong hindered bases, such as 2,5‐disubstituted pyrroles, hindered aliphatic tertiary amines, partially hindered pyridines or sulfides, or modification from tert ‐chloro‐terminated functional PIB chains reaction …”