Early propagation kinetics in the free radical polymerization of methacrylonitrile investigated by a nitroxide trapping technique
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The first seven addition products in the free radical polymerization of methacrylonitrile initiated by AIBN have been trapped by using a nitroxide trapping technique. In this experiment, the concentration of trap is maintained at a level sufficiently high to prevent the formation of high polymer, yet low enough to allow competitive monomer addition to form the lower members of the propagation series before being trapped to form the oligomeric addition products. These oligomers have been identified and quantified by electrospray ionization-mass spectrometry (ESI-MS) in series with HPLC-UV. The results have allowed individual propagation rate coefficients in the early stages of polymerization to be estimated. The variation in kpn for n = 1 and n = 3-7, where n is the number of monomer units in the propagating radical, is less than the experimental precision, with an average value at 75àof 1.9 ᠱ.0 נ104 l mol-1 s-1. As with other monomers, however, kpn for the first few propagation steps is significantly greater than the value for high polymer measured by the pulsed laser polymerization technique.