Controlled/living radical polymerization (CLRP) is one of the most rapidly developing areas in polymer science

and among the various existing techniques

nitroxide-mediated polymerization (NMP) was the first to be proposed.Most researches focused on the development of aliphatic nitroxide while few studies were devoted to the use of aromatic nitroxides in NMP.This paper describes nitroxide-mediated radical polymerization of methyl methacrylate (MMA) in the presence of 4

4'-dimethoxydiphenyl nitroxide (DMDPN) and azobisisobutyronitrile (AIBN).The aromatic nitroxide was synthesized by oxidation of 4

4'-dimethoxydiphenyl amine with oxone under biphasic conditions (CH2Cl2/H2O) in rapid and good yields.The bulk polymerization of MMA was conducted in sealed glass tubes at different conditions.The polymerization kinetics was monitored by gravimetric method while the molecular weight and its distribution of poly(methyl methacrylate) (PMMA) synthesized were determined by gel permeation chromatography.The effects of the nitroxide/initiator ratio and polymerization temperature on the polymerization kinetic

molecular weight and polydispersity index (PDI) of PMMA were investigated in detail

and reinitiation reaction experiment was conducted to verify the chain-end activity.The results showed that in this polymerization system

as the DMDPN allows delocalization of the single electron through the aromatic ring

the side reaction of -H transfer from the propagating macroradicals to the free nitroxide which would hinder the propagating process

was neglected and the chain propagation in MMA polymerization could be efficiently controlled.Molecular weight of PMMA increased linearly with monomer conversion at different DMDPN/AIBN ratios and temperatures which was different from common radical polymerization.The PMMA could be reinitiated which showed the characteristics of controlled/living radical polymerization.The polymerization rate was quite fast at low DMDPN/AIBN ratios and an induction period appeared when the ratio was too high.At the DMDPN/AIBN ratio of 1.6

the PDI was the lowest and the curve of ln(M0/M) versus time was a straight line which crossed the coordinate origin.The polymerization rate increased and PDI decreased as the polymerization temperature increased.MMA polymerization could even been operated at 70℃ though the PDI was relative higher.