Mechanism and kinetics of the imidazolidinone nitroxide-mediated free-radical polymerization of styrene



Styrene radical polymerizations mediated by the imidazolidinone nitroxides 2,5-bis(spirocyclohexyl)-3-methylimidazolidin-4-one-1-oxyl (NO88Me) and 2,5-bis(spirocyclohexyl)-3-benzylimidazolidin-4-one-1-oxyl (NO88Bn) were investigated. Polymeric alkoxyamine (PS-NO88Bn)-initiated systems exhibited controlled/living characteristics at 100–120 °C but not at 80 °C. All systems exhibited rates of polymerization similar to those of thermal polymerization, with the exception of the PS-NO88Bn system at 80 °C, which polymerized twice as quickly. The dissociation rate constants (kd) for the PS-NO88Me and PS-NO88Bn coupling products were determined by electron spin resonance at 50–100 °C. The equilibrium constants were estimated to be 9.01 × 10−11 and 6.47 × 10−11 mol L−1 at 120 °C for NO88Me and NO88Bn, respectively, resulting in the combination rate constants (kc) 2.77 × 106 (NO88Me) and 2.07 × 106 L mol−1 s−1 (NO88Bn). The similar polymerization results and kinetic parameters for NO88Me and NO88Bn indicated the absence of any 3-N-transannular effect by the benzyl substituent relative to the methyl substituent. The values of kd and kc were 4–8 and 25–33 times lower, respectively, than the reported values for PS-TEMPO at 120 °C, indicating that the 2,5-spirodicyclohexyl rings have a more profound effect on the combination reaction rather than the dissociation reaction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 327–334, 2003