Radical, AIBN

Photochemically generated radicals in chain reactions are less familiar to synthetic chemists [8,21]. The above mentioned peroxides have been used in the presence of light to initiate radical chain reactions at room or lower temperatures. Azo compounds are also known to decompose photo-lytically to afford alkyl radicals. AIBN has rarely been used under such conditions. 

Highly stereoregular PMMA macromonomers, 14, prepared by Hatada and coworkers, have recently been fractionated by supercritical fluid chromatography into completely uniform fractions with no structural distribution [20,21]. They have been oligomerized with a radical (AIBN) or an anionic initiator (3,3-dimethyl-1,1-diphenylbutyllithium). After a new fractionation by SEC comb or star polymers of completely uniform architecture are obtained. No doubt, these samples will be most promising to investigate the branched structure-property relationship. 

Because of the high propensity of the formation of radicals AIBN is used extensively for the synthesis of polymers where a radical is the initiator of a reaction ... 

Scheme 13.3 Biaryl synthesis by homolytic aromatic substitution using reactive aryl radicals (AIBN = a,a -azobisisobutyrodinitrile).

In contrast to the BPO radical, AIBN radicals should exist more freely in solution because of the difficulty of the attack on MA and weak affinity... 

EtO CN Anionic (a) nBuU, toluene, -78 to -30 C) (b) NaCN, DMSO, 25 Q free-radical (AIBN, 60°C, lOh) Polymerizes with anionic initiators no polymerization under free-radical conditions [67]... 

COOtBu Free-radical AIBN, 60-65°C, 2-butanone Polymerization observed [70]... 

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