Mechanism of initiation in the thermal polymerization of styrene. Kinetic deuterium isotope effects in the initiation step of the thermal polymerization of some deuterated styrenes

• Published in: Canadian journal of chemistry 1969-11, Vol.47 (21), p.4049-4058
• Main Authors: Kopecky, Karl R, Evani, Syamalarao
• Format: Article
• Language: English
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/v69-671

A convenient synthesis of 2,6-dideuteriostyrene starts with N,N-dimethyl-( 1 -phenylethyl)-amine which is deuterated in the 2 and 6 positions by a series of exchanges using n-butyllithium followed by deuterium oxide. The deuterium isotope effects at 70° on the rates of the thermal polymerization, , of 2,6-dideuterio-, α-deuterio-, and β,β-dideuteriostyrene are 1.29, 1.00, and 0.78, respectively. The deuterium isotope effects at 70° on the 2,2′-azobis-(2-methylpropionitrile) initiated rates of polymerization, , are 0.96, 0.86, and 0.81, respectively. From these values the deuterium isotope effects on the rates of initiation of the thermal polymerization, k 1H /k 1D , are calculated to be 1.80, 1.31, and 0.92, respectively. At 147° the presence of 1.5% potassium t-butoxide decreases the rate of the thermal polymerization of neat styrene by a factor of 17, and results in the formation of 1-phenyltetralin as the greatly predominant dimer. The results support the suggestion that the thermal polymerization of styrene is initiated by hydrogen transfer from 1-phenyl-1,2,3,9-tetrahydronaphthalene, formed by a concerted dimerization of two molecules of styrene, to a third molecule of styrene.