Thermolysis of free-radical initiators: tert-butylazocumene and its 1,3-and 1,4-bisazo and 1,3,5-trisazo analogues

Four tert-butylazocumenes (4-7) were proposed from the corresponding cyanob enzenes, and their nitrogen evolution kinetics and products were analyzed. In combination with TEMPO, the simplest compound, tert-butylazocumene (4), shows promise as a "one-fadical" initiator of styrene polymerization. The A BNQ-trapped cumyl radical 29 is a particularly stable trialkylhydroxylamine , whose thermolysis half-life is 2;1 h at 150 degreesC. Taking advantage of this stability, we trapped the cumyl radical centers from 7 to afford tris adduct 32a. While the behavior of the meta bisazoalkane 6 can be mostly pr edicted from that of 4, the para isomer 5 exhibits both unusual products an d kinetics, attributed to the formation of quinodimethane 33 via azo-contai ning radical 34. In fact, flash vacuum pyrolysis of 5 allowed observation o f the H-1 and C-13 NMR spectra of 33. whose persistence even at ambient tem perature showed that this quinodimethane is far more stable than the parent 36. Finally, evidence is presented that 7 is an initiator of star polymeri zation.