Activator generated by electron transfer for atom transfer radical polymerization

Article abstract of DOI:10.1021/ma047389l

A novel procedure was developed for activation of an oxidatively stable catalyst complex added to an atom transfer radical polymerization (ATRP). Tin(II) 2-ethylhexanoate (Sn(EH)₂) was used as a reducing agent of various Cu(II) complexes in ATRP of various monomers initiated by alkyl halides. This approach further improves a simultaneous normal and reverse initiation (SR&NI) by eliminating free radical initiators for the activation of the higher oxidation state catalyst complex. As a result, activator generated by electron transfer" (AGET) ATRP allows the preparation of pure block copolymers. Several combinations of monomer/catalyst complex precursor were studied, including styrene/CuCl₂/dNbpy, octadecyl methacrylate/CuCl₂/dNbipy, methyl methacrylate/CuCl ₂/PMDETA, n-butyl acrylate/CuBr₂/ PMDETA, and methyl acrylate/CuCl₂/Me₆TREN. Polymerization proceeded in a controlled way for all systems, producing well-defined polymers with controlled degree of polymerization and narrow molecular weight distribution, demonstrating the robust nature of AGET ATRP. Additionally, Sn(EH)₂ was used simultaneously as a reducing agent for ATRP of octadecyl methacrylate and a catalyst for ring-opening polymerization (ROP) of ∈-caprolactone, allowing direct synthesis of the corresponding block copolymer.

Full text of DOI:10.1021/ma047389l

Macromolecules 2005, 38, 4139-4146
4139
Activator Generated by Electron Transfer for Atom Transfer Radical
Polymerization
Wojciech Jakubowski and Krzysztof Matyjaszewski*
Center for Macromolecular Engineering, Department of Chemistry, Carnegie Mellon University,
4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213
Received December 20, 2004; Revised Manuscript Received March 12, 2005
ABSTRACT: A novel procedure was developed for activation of an oxidatively stable catalyst complex
added to an atom transfer radical polymerization (ATRP). Tin(II) 2-ethylhexanoate (Sn(EH)2) was used
as a reducing agent of various Cu(II) complexes in ATRP of various monomers initiated by alkyl halides.
This approach further improves a simultaneous normal and reverse initiation (SR&NI) by eliminating
free radical initiators for the activation of the higher oxidation state catalyst complex. As a result, “activator
generated by electron transfer” (AGET) ATRP allows the preparation of pure block copolymers. Several
combinations of monomer/catalyst complex precursor were studied, including styrene/CuCl2/dNbpy,
octadecyl methacrylate/CuCl2/dNbipy, methyl methacrylate/CuCl2/PMDETA, n-butyl acrylate/CuBr2/
PMDETA, and methyl acrylate/CuCl2/Me6TREN. Polymerization proceeded in a controlled way for all
systems, producing well-defined polymers with controlled degree of polymerization and narrow molecular
weight distribution, demonstrating the robust nature of AGET ATRP. Additionally, Sn(EH)2 was used
simultaneously as a reducing agent for ATRP of octadecyl methacrylate and a catalyst for ring-opening
polymerization (ROP) of ꢀ-caprolactone, allowing direct synthesis of the corresponding block copolymer.
Scheme 1. Mechanism of ATRP
Introduction
Atom transfer radical polymerization (ATRP) is one of
the most successful “controlled/living” radical polymer-
ization (CRP) developed during recent years.1-6 ATRP
relies on creation of a dynamic equilibrium between a
large amount of a dormant species and a small amount
of propagating radicals (Scheme 1).7 The propagating
Scheme 2. Methods for Conducting ATRP
•
species Pn are generated through a reversible redox
process catalyzed by a transition metal complex Mtm(L)z
(activator) that undergoes the inner-sphere one-electron
oxidation with abstraction of a radically transferable
atom or group, most frequently a halogen atom, X, from
the dormant species, PnX. The growing radicals react
reversibly with the oxidized metal complex, XMtm+1(L)z
(deactivator), to re-form the dormant species and the
activator. This process occurs with rate constants of
activation, ka, and deactivation, kda. If the concentration
of propagating radicals is sufficiently low (ka , kda), the
probability of bimolecular termination reactions is
reduced. Additionally, if initiation is fast in comparison
with propagation, molecular weight grows linearly with
conversion, and the polymerization resembles a con-
trolled/living system. Because of controlled/living nature
of ATRP, this method is used to prepare not only
homopolymers but also random,8 gradient,9 alternat-
ing,10,11 block,8,12,13 stereo-block,14 graft,15,16 branched or
hyperbranched,17-21 star,13,22 and bottle brush23-25 (co)-
polymer structures. This technique allows the controlled
polymerization of a wide range of vinyl monomers
including styrenics,26 (meth)acrylates,27-30 acryloni-
trile,31,32 vinyl acetate,33-35 and others.36,37
catalysts must be stored under an inert atmosphere.
Oxygen or other oxidants should be removed from the
system prior to addition of the catalyst in the lower
oxidation state; therefore, the process of catalyst com-
plex handling can be challenging.38-40
Reverse ATRP (Scheme 2b) was developed to over-
come this limitation. It uses the more stable Cu(II)
complexes in the initiating step. However, as more
active catalyst complexes were developed,41,42 a limita-
tion inherent in reverse ATRP became clear. The
transferable atom or group (X) is added to the reaction
However, ATRP has some limitations. Since ATRP is
initiated by a redox reaction between an initiator with
a radically transferable atom or group and a catalyst
complex comprising a transition metal compound in a
lower oxidation state (Scheme 2a), the transition metal
complexes can be easily oxidized to a higher oxidation
state. Therefore, to obtain consistent results, special
handling procedures are required, and the preformed
* Corresponding author. E-mail: km3b@andrew.cmu.edu.
10.1021/ma047389l CCC: $30.25 © 2005 American Chemical Society
Published on Web 04/21/2005

4140 Jakubowski and Matyjaszewski
Macromolecules, Vol. 38, No. 10, 2005
prolactone (CL), (Aldrich, 99%) was dried over calcium hydride
under nitrogen at 25 °C and distilled under reduced pressure
just before use (Tb ) 74-76 °C at 0.5-0.6 mmHg). 4,4′-Di-(5-
nonyl)-2,2′-bipyridine (dNbpy),46 tris(2-(dimethylamino)ethyl)-
amine (Me6TREN),42 and 1,1,1-tris(4-(2-bromoisobutyryloxy)-
phenyl)ethane (TBriBPE)47 were synthesized following previ-
ously reported procedures. N,N,N′,N′′,N′′-Pentamethyldieth-
ylenetriamine (PMDETA) (Aldrich, 99%), ethyl 2-bromoisobu-
tyrate (EtBrIB) (Acros, 98%), copper(II) chloride (Acros, 99%),
copper(II) bromide (Acros, 99%), tin(II) 2-ethylhexanoate
(Sn(EH)2) (Aldrich), anisole (Aldrich, 99%), diphenyl ether
(Acros, 99%), 2-bromoisobutyryl bromide (Aldrich, 97%), ethyl-
ene glycol (Aldrich, anhydrous), and triethylamine (Fisher
99%) were used as received. Toluene (Fisher Scientific, 99.9%)
was distilled over sodium and stored over molecular sieves.
Copper(I) chloride (Acros, 95%) and copper(I) bromide (Acros,
98%) were washed with glacial acetic acid to remove any solu-
ble oxidized species, filtered, washed with ethanol, and dried.
General Procedure for Normal ATRP of n-Butyl Acryl-
ate. TBriBPE initiator (25 mg, 3.3 × 10-2 mmol), CuBr (14
mg, 9.9 × 10-2 mmol), and CuBr2 (2.2 mg, 0.1 × 10-2 mmol)
were added to a 25 mL Schlenk flask, and the flask was
thoroughly purged by vacuum and flushed with nitrogen. Ni-
trogen-purged nBA (5.0 mL, 35 mmol) was added via syringe.
A solution of PMDETA (21 µL, 9.9 × 10-2 mmol) in degassed
anisole was added, and the mixture was stirred for 15 min in
order to preform the CuCl/PMDETA and CuBr2/PMDETA
complexes. The flask was then transferred to a thermostated
oil bath at 70 °C, and the initial kinetic sample was taken.
Samples were removed at different time intervals during
polymerization, and conversion and molecular weights were
determined by GC and GPC, respectively. The polymerization
was stopped (Mn,GPC ) 131 400, Mw/Mn ) 1.10, conversion )
88%) by opening the flask and exposing the catalyst to air.
General Procedure for SR&NI ATRP of n-Butyl Acryl-
ate. TBriBPE initiator (25 mg, 3.3 × 10-2 mmol), AIBN (8.7
mg, 5.3 × 10-2 mmol), and CuBr2 (22 mg, 9.9 × 10-2 mmol)
were added to a 25 mL Schlenk flask, and the flask was
thoroughly purged by vacuum and then flushed with nitrogen.
Degassed nBA (5.0 mL, 35 mmol) was added via syringe. A
purged solution of PMDETA (21 µL, 9.9 × 10-2 mmol) in
anisole was added, and the mixture was stirred for 15 min in
order to preform the CuBr2/PMDETA complex. The flask was
then transferred to a thermostated oil bath at 70 °C, where
decomposition of the AIBN formed the active CuBr/PMDETA
complex and the initial kinetic sample was taken. Samples
were removed at different time intervals during polymeriza-
tion, and conversion and molecular weights were determined
by GC and GPC, respectively. The polymerization was stopped
(Mn,GPC ) 43 700, Mw/Mn ) 1.45, conversion ) 81%) by opening
the flask and exposing the catalyst to air.
General Procedure for Activator Generated by Elec-
tron Transfer (AGET) for ATRP of n-Butyl Acrylate.
TBriBPE initiator (25 mg, 3.3 × 10-2 mmol) and CuBr2 (22
mg, 9.9 × 10-2 mmol) were added to a 25 mL Schlenk flask,
and the flask was thoroughly purged by vacuum and then
flushed with nitrogen. Nitrogen-purged nBA (5.0 mL, 35 mmol)
was added via syringe followed by a purged solution of
PMDETA (21 µL, 9.9 × 10-2 mmol) in anisole. Sn(EH)2 (15
µL, 4.5 × 10-2 mmol) was added, and the mixture was stirred
for 15 min in order to preform the CuBr/PMDETA complex.
The flask was then transferred to a thermostated oil bath at
70 °C, and the initial kinetic sample was taken. Samples were
removed at different time intervals during polymerization, and
conversion and molecular weights were determined by GC and
GPC, respectively. The polymerization was stopped (Mn,GPC )
86 500, Mw/Mn ) 1.09, conversion ) 63%) by opening the flask
and exposing the catalyst to air.
General Procedure for AGET ATRP of Styrene. Sty-
rene (5.0 mL, 44 mmol), CuCl2 (29.3 mg, 21.8 × 10-2 mmol),
and dNbipy (178 mg, 43.6 × 10-2 mmol) were placed in a 25
mL Schlenk flask and bubbled with nitrogen for 15 min.
Sn(EH)2 (32 µL, 9.8 × 10-2 mmol) and a purged solution of
EtBrIB (29.7 µL, 20.3 × 10-2 mmol) in toluene were added,
and the sealed flask was placed in thermostated oil bath at
as a part of the copper salt, and therefore highly active
catalysts should still be used in the amount comparable
to concentration of radical initiator. Therefore, complex
concentration cannot be independently reduced and
block copolymers cannot be formed. Simultaneous nor-
mal and reverse initiation (SR&NI) ATRP (Scheme 2c)
was developed to allow the precursors of highly active
catalyst complexes to be added to the reaction in the
higher oxidation state and at lower concentration.
SR&NI ATRP comprises a dual initiation system:
standard free radical initiators and initiators comprising
a transferable atom or group in conjunction with the
stable precursor of an active catalyst complex.43,44 This
initiation system can be used to prepare any type of
polymer that can be prepared by normal ATRP, and it
can be conducted in bulk, solution, emulsion, miniemul-
sion, and heterogeneous polymerization from surfaces.45
There are, however, some limitations to SR&NI ATRP.
Since a standard free radical initiator is still added to
the polymerization mixture to form radicals that reduce
the Cu(II), chains initiated by these radicals are always
present. These chains derived free radical initiator lead
to a partial loss of control over functionality and
topology (Scheme 2c).
This paper describes a new method for formation of
an active catalyst, a procedure for preparing an “activa-
tor generated by electron transfer” for ATRP (AGET
ATRP), which overcomes those prior problems by using
an electron transfer rather than organic radicals to
reduce the higher oxidation state transition metal.
Although many reducing agents can be applied for this
in-situ reduction, in these studies, tin(II) 2-ethylhex-
anoate (Sn(EH)2) was used to illustrate this concept
(Scheme 2d). In this new system for activation the ATRP
catalyst, the oxidized catalyst complex is reduced prior
to normal initiation of the reaction from the added
initiator molecule. This procedure has all benefits of
normal ATRP (Scheme 2a) plus the benefits of adding
a more stable catalyst complex to the reaction mixture.
The use of oxidatively stable catalyst precursors can
allow the more facile preparation, storage, and shipment
of ATRP catalyst systems. The universal character of
this approach was proved by applying the new activa-
tion/initiation process to a wide range of systems includ-
ing styrene and octadecyl methacrylate polymerized
with CuCl2/dNbpy, methyl methacrylate and n-butyl
acrylate polymerized by CuCl2/PMDETA, and methyl
acrylate using CuCl2/Me6TREN.
Since Sn(EH)2 was used as a reducing agent for the
catalyst precursor in an ATRP reaction, we sought to
expand the utility of the concept and conduct a simul-
taneous copolymerization of octadecyl methacrylate and
ꢀ-caprolactone. Sn(EH)2 was used simultaneously as the
reductive agent for AGET ATRP and as a catalyst for
ring-opening polymerization (ROP) of ꢀ-caprolactone,
allowing formation of block copolymer in a one step by
a dual mechanism.
Experimental Section
Chemicals. Styrene (St) (Aldrich, 99%), methyl methacryl-
ate (MMA) (Acros, 99%), n-butyl acrylate (nBA) (Acros 99+%),
and methyl acrylate (MA), (Aldrich, 99%) were passed through
a column filled with neutral alumina, dried over calcium
hydride, and distilled under reduced pressure. n-Octadecyl
methacrylate (ODMA) (Polysciences Inc.,99%) was purified by
dissolution in hexane and extraction four times with 5%
aqueous NaOH. After drying the organic phase over magne-
sium sulfate, the solution was passed through neutral alumina,
and the solvent was removed under reduced pressure. ꢀ-Ca-

Macromolecules, Vol. 38, No. 10, 2005
Activator Generated by Electron Transfer 4141
110 °C. The polymerization was stopped (Mn,GPC ) 14 000, Mw/
Mn ) 1.37, conversion ) 83%) by opening the flask and
exposing the catalyst to air.
The same procedure was applied for the polymerization of
octadecyl methacrylate, except that a temperature of T ) 60
°C was employed.
General Procedure for AGET ATRP of Methyl Meth-
acrylate. MMA (4.0 mL, 37 mmol) and CuCl2 (25.2 mg, 18.7
× 10-2 mmol) were added to a 25 mL Schlenk flask, and the
mixture was bubbled with nitrogen for 15 min. A purged
solution of PMDETA (39.1 µL, 18.7 × 10-2 mmol) in anisole
was added, and the mixture was stirred. Sn(EH)2 (27 µL, 8.4
× 10-2 mmol) and a purged solution of EtBrIB (27.4 µL, 18.7
× 10-2 mmol) in anisole were added, and the sealed flask was
heated in thermostated oil bath at 90 °C. The polymerization
was stopped (Mn,GPC ) 23 000, Mw/Mn ) 1.45, conversion )
79%) by opening the flask and exposing the catalyst to air.
The same procedure was applied for polymerization of
methyl acrylate, except that Me6TREN was used as ligand and
toluene as solvent and the temperature was held at 25 °C.
Procedure for Free Radical Polymerization of Methyl
Acrylate. AIBN (5.4 mg, 3.3 × 10-2 mmol) was placed in a 25
mL Schlenk flask. The flask was thoroughly purged by flushing
with nitrogen, and then degassed MA (0.6 mL, 6.4 mmol) was
added via degassed syringes. Next, Sn(EH)2 (4.0 µL, 1.2 × 10-2
mmol) in a purged solution of toluene (4.0 mL) was added, and
the sealed flask was placed in thermostated oil bath at 60 °C.
Figure 1. GPC traces of monomer ODMA and PODMA.
Conversion of ODMA was calculated by detecting decrease of
the monomer peak area.
Scheme 3. Reduction of Cu(II) to Cu(I) by Tin(II)
2-Ethylhexanoate
standards were used for calibration. Conversion of ODMA was
also determined using GPC by following the decrease of the
monomer peak area relative to the peak area of the solvent
(Figure 1). Conversion of all other monomers was determined
using a Shimadzu GC 14-A gas chromatograph equipped with
a FID detector using a J&W Scientific 30 m DB WAX
Megabore column and anisole or toluene as an internal
standard. Injector and detector temperatures were kept con-
stant at 250 °C. Analysis was carried out isothermally at 40
°C for 2 min followed by an increase of temperature to 160 °C
at a heating rate of 40 °C/min and holding at 160 °C for 3
min. Conversion was calculated by detecting the decrease of
the monomer peak area relative to the peak areas of the
standards. 1H NMR spectroscopy was performed using a
Bruker 300 MHz instrument with CDCl3 as a solvent.
The polymerization was stopped (Mn,GPC ) 64 900, Mw/Mn
1.61, conversion ) 84%) after 25 h.
)
Synthesis of Diblock Copolymer PODMA-b-PMMA by
AGET ATRP. In a 25 mL Schlenk flask, PODMA macroini-
tiator (Mw ) 13 800, PDI ) 1.10) (3.0 g, 0.2 mmol) and CuCl2
(31 mg, 7.3 × 10-5 mol) were dissolved in monomer (MMA,
9.4 g, 0.1 mol) and bubbled with nitrogen for 15 min. A purged
solution of PMDETA (48 µL, 0.23 mmol) in toluene (5 mL) was
added, and the mixture was stirred. Sn(EH)2 (34 µL, 0.1 mmol)
in toluene (4 mL) was added next, and an initial sample was
taken. Flask was placed in a thermostated oil bath at 90 °C
and stirred. The polymerization was stopped (Mn,GPC ) 38 100,
Mw/Mn ) 1.09, conversion ) 58%) by opening the flask and
exposing the catalyst to air.
Synthesis of 2-Hydroxyethyl 2-Bromoisobutyrate (HE-
BI).48 2-Bromoisobutyryl bromide (2.7 mL, 22 mmol) was
added dropwise over 2 h to a cold solution of ethylene glycol
(28.2 mL, 496 mmol) and triethylamine (2.9 mL, 22 mmol) at
0 °C. The reaction was held at 0 °C for another 2 h and then
heated to 40 °C for 5 h. The reaction mixture was cooled, added
to 500 mL of water, and extracted with chloroform three times.
The combined chloroform layers were washed successively with
diluted HCl, saturated NaHCO3, and water. The organic layer
was dried over anhydrous magnesium sulfate and evaporated
to dryness to provide the product. The product was vacuum-
distilled (yield 70%) and characterized by 1H NMR spectro-
scopy (CDCl3): (CH3)2-CBr- δ ) 1.80 (s, 6H), -CH2-CH2-
OH δ ) 3.70 (t, 2H), -CH2-CH2-OH δ ) 4.15 (t, 2H).
Simultaneous Copolymerization of E-Caprolactone
(CL) and Octadecyl Methacrylate (ODMA). CL (4.0 g, 35
mmol) and ODMA (4.0 g, 12 mmol) were added to a 25 mL
Schlenk flask, and the mixture bubbled with nitrogen for 15
min. dNbpy (164 mg, 0.40 mmol) and CuCl2 (52 mg, 0.4 mmol)
were dissolved in toluene (2 mL) in a 10 mL round-bottom flask
and transferred via syringe to the Schlenk flask. Sn(EH)2 (78
µL, 0.3 mmol) and 2-hydroxyethyl 2-bromoisobutyrate (82 mg,
0.4 mmol) were added, and the flask was placed in a thermo-
stated oil bath at 90 °C and stirred. The polymerization was
stopped(Mn,GPC ) 31 500, Mw/Mn ) 1.22, conversionCL ) 63%,
conversionODMA ) 96%) after 17 h by exposure to air, diluted
with THF, precipitated into cold methanol, and dried under
high vacuum.
Results and Discussion
A new method was developed for activation of the
catalyst complex to overcome the problem of unavoid-
able formation of small amount of homopolymers previ-
ously reported with reverse and SN&RI ATRP. This new
procedure has been termed “activator generated by
electron transfer” ATRP (AGET ATRP) since the ATRP
activator is formed from a stable catalyst precursor,
reduced by an agent which does not form radicals
capable of initiation. This novel procedure has all the
benefits of a normal ATRP process plus the benefit of
being able to add the catalyst complex in its more stable
higher oxidation state to the reaction mixture. One
requirement for the catalyst activation is that the
oxidatively stable transition metal complex should be
quickly and efficiently reduced to the desired degree by
a nonradical forming reducing agent. If this condition
is fulfilled, the reduction can be conducted in-situ.
Tin(II) 2-ethylhexanoate (Sn(EH)2) is one of the several
possible reducing agents that fulfills these require-
ments. Sn(EH)2 can reduce Cu(II) to Cu(I), as shown
by Scheme 3. To demonstrate the universality of AGET
ATRP using Sn(EH)2 as a reducing agent, different
monomer/catalyst precursor systems were studied: n-
butyl acrylate and methyl methacrylate with CuBr2/
PMDETA, styrene and octadecyl methacrylate using
CuCl2/dNbpy, and methyl acrylate with CuCl2/Me6TREN.
Comparison of Different Procedures for the
Polymerization of n-Butyl Acrylate Using a Tri-
functional Initiator. To demonstrate the prime ad-
Analysis. Molecular weight and polydispersity were deter-
mined by gel permeation chromatography (GPC). The GPC
was conducted with a Waters 515 pump and Waters 410
differential refractometer using PSS columns (Styrogel 105,
103, 102 Å) in THF as an eluent at 35 °C and at a flow rate of
1 mL/min. Linear poly(methyl methacrylate) and polystyrene

4142 Jakubowski and Matyjaszewski
Macromolecules, Vol. 38, No. 10, 2005
Table 1. Experimental Conditions and Properties of PnBA Prepared by Different ATRP Methodsa
b
ATRP method
TBriBPE/Cu(I)/Cu(II)/PMDETA/AIBN/Sn(EH)2
time (min)
conv (%)
Mn,theo
Mn,GPC
Mw/Mn
1
2
3
normal
SR&NI
AGET
1/3/0.3/3/-/-
1/-/3/3/1.6/-
1/-/3/3/-/1.4
1147
1170
1150
88
81
63
118 800
109 350
85 050
131 400
43 700
86 500
1.10
1.45
1.09
b
a [nBA]0/[TBriBPE]0 ) 1050; [nBA]0 ) 7.01 M; T ) 70 °C, anisole used as a GC standard. Mn,theo ) ([M]0/[EtBrIB]0) × conversion.
in each case to clearly show the presence of any
nonfunctionalized homopolymers in a GPC analysis of
the products. During normal ATRP (Table 1, entry 1),
the reaction was well controlled and a low polydispersity
index, PDI, was achieved (Mw/Mn ) 1.1). The high
molecular weight shoulder in the GPC traces (Figure
2) is caused by a coupling reaction commonly observed
at high monomer conversion (>90%).44 Figure 3a shows
the GPC traces for the polymers formed when nBA was
polymerized using SR&NI ATRP with AIBN (Table 1,
entry 2). A clear bimodal distribution is observed. The
low molecular weight peak is due to the presence of
linear homopolymer originally from AIBN, and the high
molecular weight peak is attributed to triarm star
polymer. In the next reaction (Table 1, entry 3) the same
conditions were used, but AIBN was replaced by Sn(EH)2,
creating the conditions for a AGET ATRP. The results,
in Table 1 (entry 3) and Figure 3b, show that a pure
star polymer was obtained without any linear polymer
byproduct. The reaction was also well controlled, and a
low PDI (1.09) was achieved. It can be concluded that
the Cu(II) complex added to the reaction mixture was
efficiently reduced to Cu(I) by reaction with tin(II)
2-ethylhexanoate in a nonradical process.
Figure 2. GPC result for a normal ATRP of nBA initiated by
a trifunctional initiator. Experimental conditions: nBA/
TBriBPE/Cu(I)/Cu(II)/PMDETA ) 1050/1/3/0.3/3; [nBA]0
7.01 M; T ) 70 °C, anisole used as a GC standard.
)
Chart 1. Structure of Trifunctional Initiator
1,1,1-Tris(4-(2-bromoisobutyryloxy)phenyl)ethane
(TBriBPE) Used in Polymerization of nBA
Effect of Sn(EH)2/Cu(II) Ratio on AGET ATRP
of ODMA. In the first series of runs ODMA was
polymerized by both normal and AGET ATRP employ-
ing different levels of a reducing agent. In the case of
the AGET ATRP dNbpy/CuCl2 was added to the reaction
as the precursor of active complex, and EtBrIB was
added as the initiator. The conditions and results of
these polymerizations are shown in Table 2. During
normal ATRP (Table 2, entry 1), the reaction was well
controlled, as evidenced by the GPC traces being mono-
modal, and a polymer with a low polydispersity was
formed (PDI ) 1.2). Next, ODMA was polymerized using
vantage of AGET ATRP, three different procedures were
used for the polymerizations of nBA: a normal ATRP,
a SN&RI ATRP, and the new AGET ATRP. The condi-
tions and results for these reactions are shown in Table
1. A trifunctional initiator, TBriBPE (Chart 1), was used
Figure 3. Evolution of molecular weight followed by GPC during SR&NI ATRP (a) vs AGET ATRP (b) for nBA polymerization
initiated by trifunctional initiator. Experimental conditions: (a) nBA/TBriBPE/Cu(I)/Cu(II)/PMDETA/AIBN/Sn(EH)2 ) 1050/1/-/
3/3/1.6/- and (b) nBA/TBriBPE/Cu(I)/Cu(II)/PMDETA/AIBN/Sn(EH)2 ) 1050/1/-/3/3/-/1.4; [nBA]0 ) 7.01 M; T ) 70 °C, anisole
used as a GC standard.

Macromolecules, Vol. 38, No. 10, 2005
Activator Generated by Electron Transfer 4143
Table 2. Experimental Conditions and Properties of PODMA Prepared by Different ATRP Methodsa
b
ATRP method
EtBrIB/Cu(I)/Cu(II)/dNbipy/Sn(EH)2
time (min)
conv (%)
Mn,theo
Mn,GPC
Mw/Mn
1
2
3
4
5
normal
1/1/0.05/2/-
1/-/1/2/2
1/-/1/2/0.9
1/-/1/2/0.45
1/-/-/-/0.45
1080
1020
1125
1100
960
95
92
98
66
11
19 000
18 400
19 600
13 200
2 200
19 600
18 300
1.23
1.45
1.34
1.10
1.5
AGET
AGET
AGET
Sn(EH)2 alone
22 800
13 800
3 100 000
b
a [ODMA]0/[EtBrIB]0 ) 60; [ODMA]0 ) 0.85 M; T ) 60 °C, in toluene (2 vol equiv vs monomer). Mn,theo ) ([M]0/[EtBrIB]0) × conversion.
Table 3. Experimental Conditions and Properties of PMMA Prepared by Different ATRP Methodsa
b
ATRP method
EtBrIB/Cu(I)/Cu(II)/PMDETA/Sn(EH)2
time (min)
conv (%)
Mn,theo
Mn,GPC
Mw/Mn
1
2
3
4
5
normal
AGET
AGET
AGET
AGET
1/1/-/1/-
180
70
145
360
360
88
77
79
78
52
17 600
15 400
15 800
15 600
10 400
27 000
23 000
23 000
14 200
9 600
1.29
1.99
1.45
1.10
1.12
1/-/1/1/2
1/-/1/1/0.45
1/-/0.4/0.4/0.18
1/-/0.2/0.2/0.09
b
a [MMA]0/[EtBrIB]0 ) 200; [MMA]0 ) 6.22 M; T ) 90 °C, in anisole (0.5 vol equiv vs monomer). Mn,theo ) ([M]0/[EtBrIB]0) × conversion.
AGET ATRP. The amounts of reducing agent, Sn(EH)2,
were varied to define conditions for better control of the
polymerization. The amounts of Sn(EH)2 used were 2.00,
0.90, and 0.45 equiv vs Cu(II). The best result was
obtained when 0.45 equiv of Sn(EH)2 was used (Table
2, entry 4). In this case, assuming that the equilibrium
represented by Scheme 3 is strongly shifted to the
products, not all of the Cu(II) will be reduced to Cu(I),
and as a result of the remaining fraction of Cu(II)
(∼10%), better control over the reaction is possible. In
all reactions polymers with monomodal molecular weight
distributions were observed. The evolution of molecular
weights for AGET ATRP of ODMA is shown by the GPC
traces in Figure 4.
Since Sn(EH)2 can reduce Cu(II) to Cu(I) species, it
can be also considered as ATRP activator. Thus, ATRP,
of ODMA was attempted in the presence of EtBrIB and
Sn(EH)2, alone, without any Cu species (Table 2, entry
5). Very low conversion (11%) and extremely low initia-
tor efficiency were observed (0.07%). The very high
molecular weight of PODMA suggests that although
Sn(EH)2 is a powerful reducing agent for Cu species, it
is a poor ATRP activator. This indicates that the
reduction plausibly occurs via outer-sphere electron
transfer rather than via inner-sphere electron transfer
(i.e., halogen atom transfer).
Effect of Initiator/Cu(II) Ratio on AGET ATRP
of MMA. MMA was polymerized by normal and AGET
ATRP employing different initiator to Cu(II) ratios. In
this case PMDETA/CuCl2 was used as the precursor of
the active complex and EtBrIB as the initiator. The
conditions and results for the reactions are shown in
Table 3. During normal ATRP (Table 3, entry 1), the
reaction was relatively well controlled as evidenced by
the monomodal molecular weight distribution and low
PDI (1.34). The amounts of Sn(EH)2 used in the AGET
ATRP were 2.00 and 0.45 equiv vs Cu(II). Similar to
the polymerization of ODMA, better results were ob-
tained when 0.45 equiv of Sn(EH)2 was used; however,
the final polymer synthesized using AGET ATRP had
a higher PDI than the polymer synthesized using
normal ATRP. Nonetheless, the polymerizations were
controlled as evidenced by the evolution of the mono-
modal GPC traces for AGET ATRP of MMA. In next
reactions (Table 3, entries 4 and 5) the amounts of Cu(II)
were decreased from 1 to 0.4 and 0.2 equiv vs initiator,
since Cu(I)/PMDETA is a relatively active catalyst for
(meth)acrylates.49,50 In both cases better results were
obtained; monomodal molecular weight distribution as
shown in Figure 5 and low PDI (1.10 and 1.12) were
observed. This also demonstrates that concentration of
Figure 4. Evolution of MW GPC traces during AGET ATRP
of ODMA. Experimental conditions: ODMA/EtBrIB/Cu(I)/
Cu(II)/dNbipy/Sn(EH)2 ) 60/1/-/1/2/0.45; [ODMA]0 ) 0.85 M;
T ) 60 °C, in toluene (2 vol equiv vs monomer).
Figure 5. Evolution of MW GPC traces during AGET ATRP
of MMA. Experimental conditions: MMA/EtBrIB/Cu(I)/Cu(II)/
PMDETA/Sn(EH)2 ) 200/1/-/0.2/0.2/0.09; [MMA]0 ) 6.22 M;
T ) 90 °C, in anisole (0.5 vol equiv vs monomer).

4144 Jakubowski and Matyjaszewski
Macromolecules, Vol. 38, No. 10, 2005
Table 4. Experimental Conditions and Properties of PS Prepared by Different ATRP Methodsa
b
ATRP method
EtBrIB/Cu(I)/Cu(II)/dNbipy/Sn(EH)2
time (min)
conv (%)
Mn, theo
Mn, GPC
Mw/Mn
1
2
3
normal
AGET
AGET
1/1/-/2/-
1/-/1/2/0.45
1/-/0.4/0.8/0.18
1580
420
420
95
83
64
19 000
17 200
12 800
15 600
14 000
8 500
1.27
1.37
1.22
b
a [St]0/[EtBrIB]0 ) 200; [St]0 ) 8.72 M; T ) 110 °C, toluene used as a GC standard. Mn,theo ) ([M]0/[EtBrIB]0) × conversion.
Table 5. Experimental Conditions and Properties of PMA Prepared by Different ATRP Methodsa
b
ATRP method
EtBrIB/Cu(I)/Cu(II)/Me6TREN/Sn(EH)2
time (min)
conv (%)
Mn,theo
Mn,GPC
Mw/Mn
1
2
normal
AGET
1/1/0/1/-
1/-/1/1/0.45
1110
2760
96
61
19 200
12 100
18 000
13 100
1.30
1.16
b
a [MA]0/[EtBrIB]0 ) 230; [MA]0 ) 5.37 M; T ) 25 °C, in toluene (1 vol equiv vs monomer). Mn,theo ) ([M]0/[EtBrIB]0) × conversion.
Sn/Cu(II) can be varied independently of the initiator
concentration to optimize the control of the reaction.
AGET ATRP of Styrene (St) and Methyl Acrylate
(MA). The universal character of AGET ATRP was
investigated by polymerization of other types of mono-
mers with different catalyst systems: styrene with
CuCl2/dNbpy and methyl acrylate using CuCl2/Me6TREN.
In each case, the product formed in a normal ATRP was
compared to the product formed using AGET ATRP.
For the polymerization of styrene, dNbpy/CuCl2 was
added to the reaction as the oxidatively stable precursor
of an active catalyst complex. The conditions and results
for normal and AGET ATRP are shown in Table 4. All
reactions were well controlled with experimental mo-
lecular weights being close to theoretical values. How-
ever, a slightly higher PDI (1.37) was observed for
AGET ATRP when used amount of Cu(II) vs initiator
was 1:1 (Table 4, entry 2) although the final GPC traces
remained monomodal. Decreasing the ratio of Cu(II)/
initiator to 0.3 in AGET ATRP (Table 4, entry 3)
resulted in better controlled reaction and a final polymer
with lower PDI (1.22) (Figure 6).
pure Cu(I) was employed initially. To ensure the slower
rate of polymerization was not due to interaction of
Sn(EH)2 with the monomer or growing polymer chain
end, two conventional radical polymerization were per-
formed, with and without Sn(EH)2. The rates of both
polymerizations were the same, indicating that AGET
ATRP was slower than normal ATRP plausibly due to
the difference in the concentration of Cu(II) for each sys-
tem with the result that the AGET ATRP was better
controlled and the final polymer had a lower PDI, due
to efficient deactivation of growing species by Cu(II). The
GPC traces showed monomodal distributions of molecu-
MA was also polymerized by both normal and AGET
ATRP; in this case Me6TREN/CuCl2 was used to gener-
ate the active complex, and EtBrIB was added as the
initiator. The conditions used for the reactions and the
results are shown in Table 5. Figure 7 shows the kinetic
plot for the reactions, and it can be seen that the normal
ATRP was faster then the AGET ATRP. This is plau-
sibly due to incomplete reduction of Cu(II) to Cu(I). The
remaining Cu(II) slows down the reaction due to an
increased rate of deactivation, and the final rate of the
AGET polymerization is lower than normal ATRP, where
Figure 7. Kinetic plot for ATRP of MA. Experimental
conditions: [MA]0 ) 5.37 M; T ) 25 °C, in toluene (1 vol equiv
vs monomer).
Figure 6. Evolution of MW GPC traces during AGET ATRP
of St. Experimental conditions: St/EtBrIB/Cu(I)/Cu(II)/dNbipy/
Sn(EH)2 ) 200/1/-/0.4/0.8/0.18; [St]0 ) 8.72 M; T ) 110 °C,
toluene used as a GC standard;
Figure 8. Evolution of MW GPC traces during AGET ATRP
of MA. Experimental conditions: MA/EtBrIB/Cu(I)/Cu(II)/Me6-
TREN/Sn(EH)2 ) 230/1/-/1/1/0.45; [MA]0 ) 5.37 M; T ) 25
°C, in toluene (1 vol equiv vs monomer).

Macromolecules, Vol. 38, No. 10, 2005
Activator Generated by Electron Transfer 4145
Table 6. Experimental Conditions and Properties of Block Copolymer PODMA-b-PMMA Prepared by Step Method Using
AGET ATRP
time
(min)
conv
(%)
c
ATRP method
initiator/Cu(I)/Cu(II)/ligand/Sn(EH)2
Mn, theo
Mn, GPC
Mw/Mn
1
2
PODMAa
AGET
AGET
1/-/1/2/0.45
1/-/1/1/0.45
1100
120
66
58
13 200
37 200
13 800
38 100
1.10
1.09
PODMA-b-PMMAb
a [ODMA]0/[EtBrIB]0 ) 60; [ODMA]0 ) 0.85 M; T ) 60 °C, in toluene (2 vol equiv vs monomer). b [MMA]0/[PODMA]0 ) 400; [MMA]0
c
) 6.22 M; T ) 90 °C, in anisole (0.5 vol equiv vs monomer). Mn,theo ) ([M]0/[EtBrIB]0) × conversion.
Table 7. Experimental Conditions and Properties of Block Copolymer Prepared by Simultaneous Copolymerization of
Octadecyl Methacrylate and E-Caprolactonea
b
b
solvent
toluene
T (°C)
time (min)
1020
conv CL [%]
0.63
conv ODMA [%]
0.96
Mn,GPC
Mw/Mn
FCL
0.30
FODMA
1
PCL-b-PODMAa
75
31 500
1.22
0.70
a [ODMA]0:[CL]0:[HEBI]0:[Sn(EH)2]0:[CuCl2]0:[dNbipy2]0 ) 30:85:1: 0.6:1:1; [ODMA]0 ) 1.25 M. b Measured by 1H NMR spectroscopy.
lar weights (Figure 8). These results are in agreement
with the preceding studies of ATRP of MA in the pres-
ence of Me6TREN.42,51 The Me6TREN ligand generates
the most reducing copper complexes, and Sn(EH)2 plaus-
ibly cannot reduce it completely to the Cu(I) state.52,53
Preparation of a Block Copolymer by a Two-
Step Method Using AGET ATRP. AGET ATRP was
used in the two-step synthesis of block copolymer
PODMA-b-PMMA. First, PODMA block was prepared
using AGET ATRP and then used as a macroinitiator.
Extension with MMA using AGET ATRP was very
efficient. Table 6 shows the experimental conditions and
properties of synthesized polymers. Figure 9 presents
the SEC chromatograms recorded after each step. The
reactions were well controlled, as evidenced by the GPC
traces being monomodal, and final block copolymer with
a narrow polydispersity was formed (PDI ) 1.09).
Preparation of a Block Copolymer by Simulta-
neous Polymerization of Octadecyl Methacrylate
and E-Caprolactone. Sn(EH)2 was concurrently used
as a reducing agent for ATRP and as a catalyst for ring-
opening polymerization (ROP), allowing copolymeriza-
tion of octadecyl methacrylate and ꢀ-caprolactone. In
this case, each monomer should independently propa-
gate via two different mechanisms (radical and pseudoan-
ionic), forming a block copolymer. The results shown in
Table 7 prove that the block copolymerization was
successful. GPC traces showed monomodal distributions
1
(Figure 10), and H NMR spectra obtained after syn-
Figure 9. GPC traces after each step of synthesis of block
copolymer PODMA-b-PMMA. Experimental conditions: POD-
MA: ODMA/EtBrIB/Cu(I)/Cu(II)/dNbipy/Sn(EH)2 ) 60/1/-/1/
2/0.45; [ODMA]0 ) 0.85 M; T ) 60 °C, in toluene (2 vol equiv
vs monomer); PODMA-b-PMMA: MMA/PODMA/Cu(I)/Cu(II)/
Me6TREN/Sn(EH)2 ) 400/1/-/1/1/0.45; [MMA]0 ) 6.22 M; T
) 90 °C, in anisole (0.5 vol equiv vs monomer).
Figure 11. Comparison of 1H NMR spectra of pure PCL, pure
PODMA and PCL-b-PODMA block copolymer synthesized by
simultaneous copolymerization. Experimental conditions: OD-
MA/CL/HEBI/Sn(EH)2/CuCl2/dNbipy ) 30:85:1: 0.6:1:1; [OD-
MA]0 ) 1.25 M; in toluene (1 vol equiv vs CL), T ) 75 °C.
Figure 10. Evolution of MW GPC traces during simultaneous
polymerization of ODMA and CL. Experimental conditions:
ODMA/CL/HEBI/Sn(EH)2/CuCl2/dNbipy ) 30:85:1: 0.6:1:1;
[ODMA]0 ) 1.25 M; in toluene (1 vol equiv vs CL), T ) 75 °C.

4146 Jakubowski and Matyjaszewski
Macromolecules, Vol. 38, No. 10, 2005
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thesis (Figure 11) indicate that a diblock copolymer was
formed.
Conclusion. A new method for conducting ATRP was
developed. The procedure used to generate activator
relies on electron transfer rather than reduction by
organic radicals; therefore, this method is called AGET
ATRP. This novel procedure has all the benefits of a
normal ATRP process combined with the additional
benefit of adding the catalyst complex to the reaction
mixture in its more stable higher oxidation state. Tin(II)
2-ethylhexanoate (Sn(EH)2) was used as the reducing
agent in this series of examples, demonstrating the
benefits of the procedure.54 The universal character of
AGET ATRP was illustrated by applying the new
process to the polymerization of several monomers with
various catalyst precursors. The reduced in situ active
catalyst complexes achieved controlled polymerization
with a range of monomers that resulted in synthesis of
well-defined polymers with controlled degree of poly-
merization and molecular weight distribution. In con-
trary to reverse ATRP, concentration of active catalyst
in AGET ATRP can be change independently of the
initiator to improve control of reactions. A successful
synthesis of block copolymer using AGET ATRP was
achieved. In addition, simultaneous block copolymeri-
zation of octadecyl methacrylate and ꢀ-caprolactone was
conducted with Sn(EH)2 acting in a dual role of a
reducing agent for AGET ATRP and a catalyst for ring-
opening polymerization (ROP) in the same reaction
vessel. The use of oxidatively stable catalyst precursors
can potentially allow the more facile preparation, stor-
age, and shipment of ATRP catalyst systems.
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Acknowledgment. The authors thank the National
Science Foundation (DMR-00-09409) and the members
of the CRP Consortium at Carnegie Mellon University
for their financial support.
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