The kinetics of polymerization of α‐vinylnaphthalene

Abstract

AbstractThe kinetics of the 2,2′‐azobisisobutyronitrile (AIBN)‐initiated bulk polymerization of α‐vinylnaphthalene (AVN) at 50, 60, and 70°C. is reported. The polymerization rate is proportional to the 1/2 power of the initiator concentration and the first power of the monomer concentration, and the ratio of the termination rate constant to the square of the propagation rate constant is slightly less than for styrene. Unlike styrene, however, very low molecular weight polymers (ca. 2000–6000) are obtained throughout the entire conversion of monomer to polymer. The molecular weight is shown to be controlled by a chain transfer reaction with the monomer, the value of the transfer constant being about 0.03 at 50, 60, and 70°C., about 300 times that of the monomer transfer constant for styrene. The transfer reaction is attributed to an attack of a growing polymer radical on the naphthalene ring of the AVN. In support of this, the transfer constant of the polystyryl radical with naphthalene was also found to be large (1.1 × 10−3), about 600 times that of the transfer constant (1.86 × 10−6 at 60°C.) of the same radical with benzene. A transfer constant of similar magnitude was obtained for the polynaphthalyl radical with naphthalene. This greater polystyryl radical affinity for naphthalene over benzene is in excellent agreement with expectations based on methyl radical affinities for these same substrates. The greater value of the monomer transfer constant of AVN over that of the polynaphthalyl or polystyryl radicals with naphthalene suggests an activation of the naphthalene ring in AVN. The differences in the polymerization kinetics of AVN and vinyl benzoate are discussed. The overall second‐order thermal rate constant for AVN is found to be about eight times that for styrene at the same temperature. Overall activation energies of 21.5 and 17.4 kcal./mole are obtained for the initiated and purely thermal polymerizations, respectively. An empirical intrinsic viscosity‐molecular weight relation for AVN polymer is given.