Determination of the Relative Rates of Addition of Styrene and Acrylonitrile to the 1-(1,3-Diphenylpropyl) and 1-(3-Cyano-1-phenylpropyl) Radicals. Evidence for a Penultimate Effect in Radical Copolymerization

Article abstract of DOI:10.1021/ja00201a041

1,1'-Azobis(1,3-<1-(13)C>diphenylpropane) (1b) and 4,4'-azobis(4-phenyl<4-(13)C>butyronitrile) (1c) were prepared in overall yields of 10percent and 1.2percent, respectively, both starting from Ba(13)CO3 (99 atom percent).Analysis of end-group concentrations in styrene-acrylonitrile (SAN) copolymers prepared with 1b as initiator allows accurate determination of the relative rates of addition of these monomers (k_S/k_A) to the 1-(1,3-diphenylpropyl) radical (2b); similarly, analysis of SAN copolymers prepared with 1c allows determination of k_S/k_A for the 1-(3-cyano-1-phenylpropyl)radical (2c).Significantly different preferences of the radicals for addition of styrene and acrylonitrile were observed; we obtain k_S/k_A=0.21 +/- 0.01 for 2b and K_S/k_A=0.52 +/- 0.03 for 2c.These results show that k_S/k_A for 1-(1-phenylalkyl) radicals is sensitive to substitution γ to the radical center and provide strong support for the existence of a penultimate unit effect in SAN copolymerization.The results are consistent with the penultimate model analysis of SAN copolymerization by Hill, O'Donnell, and O'Sullivan.