Retarded Anionic Polymerization: Copolymerization of Butadiene and Styrene in the Presence of Alkyllithium and n,s-Dibutylmagnesium or Triisobutylaluminium Derivatives

✍ Scribed by Stéphane Carlotti; Stéphane Ménoret; Anna Barabanova; Philippe Desbois; Alain Deffieux

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 154 KB
• Volume: 205
• Category: Article
• ISSN: 1022-1352
• DOI: 10.1002/macp.200300118

✦ Synopsis

Abstract

Summary: The influence of Lewis acid additives on the anionic butadiene polymerization using lithium as a counter ion in non‐polar solvent is investigated. A decrease of the polymerization rate was always observed. In the presence of n,s‐Bu~2~Mg the percentage of 1,2‐vinyl units increases with the [Mg]/[Li] ratio. This evolution can be explained by further complexation of lithium with free dialkylmagnesium modifying the nature of the propagating species and/or possible 1,4 to 1,2 isomerization during chain exchanges between lithium and magnesium derivatives. As a result of the transmetallation process, 0.5 to 1 supplementary chains are formed by magnesium depending on the [Mg]/[Li] ratio. In contrast, the ^i^Bu~3~Al/RLi system does not yield any modification of polybutadiene microstructure, which remains close to the one observed with s‐BuLi alone. The determination of the reactivity ratios in styrene‐butadiene copolymerization shows that tapered‐like copolymers are obtained in the presence of both n,s‐Bu~2~Mg and ^i^Bu~3~Al. However the magnesium derivative induces a lesser increase of styrene incorporation in the copolymer than the aluminium additive. The observed microstructure and reactivity ratios support that the monomer insertion proceeds directly into heterocomplexes.

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