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Keywords:

  • radical polymerization;
  • living polymerization;
  • X-ray;
  • kinetics (polym.);
  • nitroxide

Abstract

The 2,6-spirodicyclohexyl substituted nitroxide, cyclohexane-1-spiro-2′-(3′,5′-dioxo-4′-benzylpiperazine-1′-oxyl)-6′-spiro-1″-cyclohexane (BODAZ), was investigated as a mediator for controlled/living free-radical polymerization of styrene. The values of the number-average molecular weight increased linearly with conversion, but the polydispersities were higher than for the corresponding 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) and 2,5-bis(spirocyclohexyl)-3-benzylimidazolidin-4-one-1-oxyl (NO88Bn) mediated systems at approximately 2.2 and 1.6 at 100 and 120 °C, respectively. These results were reflected in the rate coefficients obtained by electron spin resonance spectroscopy; at 120 °C, the values of the rate coefficients for polystyrene-BODAZ alkoxyamine dissociation (kd), combination of BODAZ and propagating radicals (kc), and the equilibrium constant (K) were 1.60 × 10−5 s−1, 5.19 × 106 M−1 s−1, and 3.08 × 10−12 M, respectively. The value of kd was approximately one and two orders of magnitude lower, and that of K was approximately 20 and 7 times lower than for the NO88Bn and TEMPO adducts. These results are explained in terms of X-ray crystal structures of BODAZ and NO88Bn; the six-membered ring of BODAZ deviates significantly from planarity as compared to the planar five-membered ring of NO88Bn and possesses a benzyl substituent oriented away from the nitroxyl group leading to a seemingly more exposed oxyl group, which resulted in a higher kc and a lower kd than NO88Bn. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3892–3900, 2003