Chemistry Reference
In-Depth Information
removal of the catalyst complex was possible from the reaction mixture. The Janda Jel ligands were
used in ATRP of methyl methacrylate, styrene, and 2-(dimethylamino)ethyl methacrylate. The methyl
methacrylate and 2-(dimethylamino)ethyl methacrylate polymerizations proceeded quickly to high
conversion (
90%) and were well controlled. The styrene polymerization, however, was found by
them to be sluggish and proceeded only to 63% conversion. After polymerizations were complete, the
catalyst ligand complex was easily removed by filtration. Zhu and coworkers [
257
] claim to have a
simple and effective method for purification of an ATP product using catalyst precipitation and
microfiltration. The method relies on the precipitation of the Cu + Br ligand catalyst complex by the
additions of Cu++Br
2
. The precipitate thus formed is effectively retained by a 0.14-
>
m
m PTFE filter,
resulting in up to 99.9% of the catalyst being removed from the polymer. The resulting clear polymer
filtrate contains little residual copper, down to 10 ppm.
Matyjaszewski and coworkers developed a process [
255
] for an electrochemically mediated
ATRP. They use applied voltage to drive the production of Cu + ions that catalyze the polymer
formation. Because the rate of the reaction is controlled by a redox equilibrium between cuprous and
cupric ions, electrochemistry permits the regulation of the concentration of each species.
-e
-
R
Cu(II)Br
2
/Ligand
RBr +
Cu(I)Br/Ligand
+
+e
-
polymer
A similar ATP process is one that uses iron(II) bis(triphenylphosphine)-dichloride[FeCl
2
(PPh
3
)
2
]. It
induces “living” polymerization of monomers such as methyl methacrylate in conjunctionwith organic
halides as initiators in the presence and in the absence of Al(O
i
Pr)
3
in toluene at 80
C. The molecular
weight distributions of the products are 1.1-1.3 [
269
]. The following mechanism is visualized [
269
]:
MMA
Fe(II
)
MMA
X
R
X
X
Fe(III)
R
R
-Fe(II)
Fe(II)
CO
2
CH
3
Fe(II)
X
R
R
X
Fe(III)
Reversible
CO
2
CH
3
CO
2
CH
3
Dormant species
Active radical species
The ATP process developed by Sawamoto and coworkers [
226
], uses an initiating system
consisting
of
carbon
tetrachloride,
dichlorotri(triphenyl-phosphine)-ruthenium (II)
and
tert
methylaluminum bis(2,6-di-
-butylphenoxide) to polymerize methyl methacrylate [
226
]. The
polymerization involves reversible and homolytic cleavages of carbon-halogen terminal groups
assisted by transition metal complexes [
226
].
RuCl
2
(PPh
3
)/
MeAl (ODBP
)
Cl
Cl
Revesible
Homolitic
R
R
