Primary Hydroxy-Terminated Polyisobutylene via End-Quenching with a Protected N-(ω-Hydroxyalkyl)pyrrole

Abstract

N-(2-tert-Butoxyethyl)pyrrole was used to end-quench TiCl 4 -catalyzed quasiliving isobutylene polymerizations initiated from 2-chloro-2,2,4-trimethylpentane and 5-tert-butyl-1,3-di(2-chloro-2-propyl)benzene at -60°C in 60/40 (v/v) hexane/methyl chloride. End-capping was near-quantitative except for the formation of <5% exo-olefin chain ends, with alkylation occurring in both the C-3 (57%) and C-2 (38%) position on the pyrrole ring. Coupling was not observed for the monofunctional polymers; however, quenching of difunctional polymers resulted in small amounts of coupling due to dialkylation at the pyrrole ring. The terminal tert-butyl group of the N-(2-tert-butoxyethyl)pyrrole-capped polyisobutylene was rapidly and quantitatively removed in situ by addition of ethylaluminum dichloride and sulfuric acid to the reaction mixture. Furthermore, heating the reaction mixture to reflux (69°C) forced alkylation by the residual exo-olefin chain ends and induced isomerization of the pyrrole-capped chain ends to yield exclusively [3-polyisobutyl-N-(2-hydroxyethyl)]pyrrole. The primary hydroxy-terminated polyisobutylenes showed excellent, unimpeded reactivity with carboxylic acid and isocyanates typically used in block copolymer synthesis.

Polyisobutylene‐based polyurethanes with unprecedented properties and how they came about

“…6). 28, 29 And a further method to produce HO‐PIB‐OH was by reaction of N ‐(2‐ tert ‐butoxyethyl)pyrrole followed by cleavage of the terminal tert ‐butyl ether 30…”

“…28,29 And a further method to produce HO-PIB-OH was by reaction of N-(2-tert-butoxyethyl)pyrrole followed by cleavage of the terminal tert-butyl ether. 30 The prim amine telechelic PIB (H 2 N-PIB-NH 2 ) was obtained quantitatively from the ACH 2 CH 2 CH 2 -Br derivative in two steps by the Gabriel route, 31 that is, by converting the bromide to the corresponding phthalimide followed by hydrazinolysis ( Fig. 7).…”

Functionalization of polyisobutylene and polyisobutylene oligomers via the ritter reaction

“…More recently, quantitative exo ‐olefin‐terminated PIB has been synthesized by direct “end‐quenching” of living carbocationic PIB chain ends via addition reaction with methallyltrimethylsilane or elimination reactions induced by hindered bases, alkoxysilanes, alkyl ethers, or alkyl sulfides . End‐quenching has also allowed for the direct functionalization of living PIB with functional groups other than exo ‐olefin, using quencher molecules of several characteristic types including olefins that add only once to the chain, alkoxybenzenes, and heterocyclic aromatics . To effectively functionalize PIB, a quencher molecule must preferentially react with the carbocationic chain end, rather than the more abundant Lewis acid, and the quenching reaction must compete kinetically with decomposition pathways of the carbocation, particularly carbocation rearrangement …”

Syntheses of terminally functionalized polyisobutylene derivatives using diazonium salts

“…Polyisobutylene (PIB) is an important polymer and many procedures can be used to prepare terminally‐functionalized derivatives of this polyolefin. For example, a variety of elegant and sophisticated chemistry can be used during a cationic polymerization to introduce terminal groups via functional initiators and during or after a termination step 1–12. However, as PIB polymers with terminal alkene functionality are commercially available,13 postpolymerization modification reactions are also useful and of interest especially for groups not equipped to carry out living cationic polymerization chemistry.…”

“…For example, a variety of elegant and sophisticated chemistry can be used during a cationic polymerization to introduce terminal groups via functional initiators and during or after a termination step. [1][2][3][4][5][6][7][8][9][10][11][12] However, as PIB polymers with terminal alkene functionality are commercially available, 13 postpolymerization modification reactions are also useful and of interest especially for groups not equipped to carry out living cationic polymerization chemistry. Our group has recently described a number of examples of terminally-functionalized PIB oligomers that are useful in organic synthesis and catalysis.…”