Controlled/living radical polymerization (CLRP) is one of themost rapidly developingareas in polymer science. Amongthe various existing techniques
nitroxide-mediated polymerization (NMP) was the first to be proposed. Up to now
most of the nitroxides studied in NMP are dialkyl or alkyl-arylnitroxides
while the use of diarylnitroxides as control radicals has not been extensively studied. In this paper
4
4'-dimethoxydiphenyl nitroxide (DMDPN) and its corresponding alkoxyamine initiator were easily synthesized and used to mediate the polymerization of methyl methacrylate (MMA). DMDPN was highly stable at high temperature and the single electron delocalisation on the aromatic rings prevented the undesired hydrogen abstraction between the nitroxide and the propagating radical chain. The polymerization kinetics was monitored by gravimetric method while the molecular weight and the distribution of poly(methyl methacrylate) (PMMA) synthesized were determined by gel permeation chromatography (GPC).The dissociation rate constants (
k
d
) of the DMDPN-based alkoxyamine initiator wasdetermined by electron spin resonance (ESR) experiments performed at temperatures ranging from 100℃ to 120 ℃
yielded thefollowing Arrhenius parameters:
E
a
=135.2 kJ·mol
-1
and
A
=3×10
14
. The
k
d
value of macromolecular species was also determined at 110 ℃. As the low steric hindrance around the aminoxyl group in DMDPN
the penultimate unit effect
which was significant in a MMA/SG1(
N
-
tert
-butyl-
N
-(1-diethyl-phosphono-2
2-di-methylpropyl) nitroxide) system
had only a weak influence on
k
d
in the MMA/DMDPN system. A 6-fold increase of
k
d
between the DMDPN-based alkoxyamine initiator and PMMA-DMDPN macro-alkoxyamine was observed. A bulkpolymerization of MMA was performed at 110 ℃ using 1 mol% of DMDPN-based alkoxyamine in the presence of 0.5 mol% of the corresponding free nitroxide to determine the equilibrium constant
K
. The recombination rate constant (
k
c
) was then derived from the constant
K
. A Fischer's diagram for the polymerization of MMA at 110℃ was made and the values of
k
d
and
k
c
lied in the living and controlled area
proving the livingness of this polymerization system.
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