Coupling reaction of polyisoprenyllithium with 1,2-dibromoethane

✍ Scribed by Gian Tommaso Viola; Claudio Cavallo

• Book ID: 101268204
• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 306 KB
• Volume: 35
• Category: Article
• ISSN: 0887-624X
• DOI: 10.1002/(sici)1099-0518(19970115)35:1<17::aid-pola3>3.0.co;2-#

✦ Synopsis

The coupling reaction of polyisoprenyllithium with 1,2-dibromoethane (DBE) gives a multimodal molecular weight distribution (MWD). Species with molecular weights three and four times (P 3 , P 4 ) higher than the base polymer (P) are present beside the main expected one with double molecular weight (P 2 ). The relative abundancies of P, P 2 , P 3 , and P 4 depend on the experimental conditions. Gas-phase chromatographic analysis carried out during the coupling reaction show the presence of ethylene whose formation is related to a lithium-bromine exchange reaction competing with direct alkylation. The lithium-bromine exchange reaction is more effective at T õ 80ЊC and results in the formation of allyl bromide-terminated polyisoprene, while direct alkylation is effective at T ú 100ЊC and yields alkyl bromide chain ends. The allylic and alkylic bromides react differently with the remaining polyisoprenyllithium: the former adds only to polyisoprenyllithium yielding P 2 , while the later also yields P 3 and P 4 through radical reactions.