Effect of ethyl aluminium sesquichloride on the relative reactivities of styrene and methyl methacrylate towards the 1-cyano-1-methylethyl and the 1-methyl-1-(methoxycarbonyl)ethyl radicals

✍ Scribed by R.A. Lyons; G. Moad; E. Senogles

• Publisher: Elsevier Science
• Year: 1993
• Tongue: English
• Weight: 489 KB
• Volume: 29
• Category: Article
• ISSN: 0014-3057
• DOI: 10.1016/0014-3057(93)90109-s

✦ Synopsis

Akstraet~opolymers of styrene (S) and methyl methacrylate (MMA) have been prepared with different concentrations of ethyl aluminium sesquichloride (EASC) using t3C-enriched forms of azo-bis-(methylisobutyrate) (AIBMe) and azo-bis-(isobutyronitrile) (AIBN). The end-group and overall structure of the copolymers have been examined using ~H-and ~3C-NMR. It has been established that when EASC is present both the 1-methyl-l-(methoxycarbonyl)ethyl and l-cyano-l-methylethyl radicals prefer to add S over MMA by a factor of approx. 20. In contrast, in the absence of EASC the reactivity ratio, kMMA/ks, for these radicals is 0.70 and 0.56, respectively. The change in selectivity is attributed to complex formation between the initiating radicals and EASC. Copolymers prepared with AIBN were alternating even with MMA in excess over the Lewis acid by a factor of ~47. When AIBMe was used as the initiator the copolymers obtained, with similar reaction conditions, show deviation from an alternating structure. An explanation to account for the observed results is proposed.