The Kinetics of enhanced spin capturing polymerization: Influence of the nitrone structure

Edgar H.H. Wong, Martina H. Stenzel, Thomas Junkers, Christopher Barner-Kowollik

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Several nitrones and one nitroso compound have been evaluated for their ability to control the molecular weight of polystyrene via the recently introduced radical polymerization method of enhanced spin capturing polymerization (ESCP). In this technique, molecular weight control is achieved (at ambient or slightly elevated temperatures) via the reaction of a growing radical chain with a nitrone forming a macronitroxide. These nitroxides subsequently react rapidly and irreversibly with propagating macroradicals forming polymer of a certain chain length, which depends on the nitrone concentration in the system. Via evaluation of the resulting number-average molecular weight, Mn, at low conversions, the addition rate coefficient of the growing radicals onto the different nitrones is determined and activation energies are obtained. For the nitrones N-tert-butyl-α- phenylnitrone (PBN), N-methyl-α-phenylnitrone (PMN), and N-methyl-α-(4-bromo-phenyl) nitrone (pB-PMN), addition rate coefficients, kad,macro, in a similar magnitude to the styrene propagation rate coefficient, kp, are found with spin capturing constants C SC (with CSC = kad,macro/kv) ranging from 1 to 13 depending on the nitrone and on temperature. Activation energies between 23.6 and 27.7 kJ mol-1 were deduced for kad,macro, congruent with a decreasing CSC with increasing temperature. Almost constant Mn over up to high monomer to polymer conversions is found when CSC is close to unity, while increasing molecular weights can be observed when the CSC is large. From temperatures of 100 °C onward, reversible cleavage of the alkoxyamine group can occur, superimposing a reversible activation/deactivation mechanism onto the ESCP system.

Original languageEnglish
Pages (from-to)1098-1107
Number of pages10
JournalJournal of Polymer Science, Part A: Polymer Chemistry
Issue number4
Publication statusPublished - 15 Feb 2009
Externally publishedYes


  • Activation energy
  • Controlled radical polymerization
  • Degree of polymerization (DP)
  • ESR spin traps
  • Kinetics (polym.)
  • Nitrone
  • Polystyrene
  • Structure-reactivity relations

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