Synthesis of ABC 3-miktoarm star terpolymers from a trifunctional initiator by combining ring-opening polymerization, atom transfer radical polymerization, and nitroxide-mediated radical polymerization

Article abstract of DOI:10.1021/ma036010c

We report a new method to synthesize ABC 3-miktoarm star terpolymers by combining three different controlled/"living" polymerization techniques: ring-opening polymerization (ROP), atom transfer radical polymerization (ATEP), and nitroxide-mediated radical

Full text of DOI:10.1021/ma036010c

3128
Macromolecules 2004, 37, 3128-3135
Synthesis of ABC 3-Miktoarm Star Terpolymers from a Trifunctional
Initiator by Combining Ring-Opening Polymerization, Atom Transfer
Radical Polymerization, and Nitroxide-Mediated Radical Polymerization
Ta o He, Dejin Li, Xia Sh en g, a n d Bin Zh a o*
Department of Chemistry, University of Tennessee at Knoxville, Knoxville, Tennessee 37996
Received December 29, 2003; Revised Manuscript Received February 29, 2004
ABSTRACT: We report a new method to synthesize ABC 3-miktoarm star terpolymers by combining
three different controlled/“living” polymerization techniques: ring-opening polymerization (ROP), atom
transfer radical polymerization (ATRP), and nitroxide-mediated radical polymerization (NMRP). A
trifunctional initiator bearing a hydroxy group, an ATRP initiator, and a NMRP initiator was designed
1
and synthesized. The structure was confirmed by H NMR, 13C NMR, and mass spectroscopy. ABC star
terpolymers were then prepared from the trifunctional initiator by sequential ROP of ꢀ-caprolactone,
ATRP of methyl methacrylate, and NMRP of styrene. GPC and kinetic analysis indicated that the
polymerizations were controlled. The 3-miktoarm star structure was further confirmed by cleavage of a
star terpolymer.
In tr od u ction
nonhomopolymerizable macromonomer techniques. Non-
homopolymerizable macromonomers with 1,1-diphenyl-
ethylene groups at one end were reacted with a living
polymer, producing an active species at the junction of
diblock copolymers followed by the polymerization of the
third monomer. Fujimoto et al. prepared star terpoly-
mers of PS, poly(dimethylsiloxane), and poly(tert-butyl
methacrylate) by this method.6 Similar strategies were
also used in the synthesis of star terpolymers of PS,
polybutadiene, and poly(methyl methacrylate) (PMMA)
(or poly(2-vinylpyridine))12,13 and other star copoly-
mers.14
ABC 3-miktoarm star terpolymers are molecules
composed of three different polymer chains emanating
from a central junction point.1-9 If all three arms are
sufficiently long and the Flory-Huggins interaction
parameters for all pairs are sufficiently large, mi-
crophase separation will occur, resulting in ordered
morphologies comprised of nearly pure microdomains
of each of the components. Unlike linear diblock and
multiblock copolymers in which the junctions between
different blocks are uniformly distributed over the
interfaces between the domains, the junction points in
ABC star terpolymers are restricted to periodically
spaced parallel lines defined by the mutual intersection
of the different domains due to the specific molecular
architecture of star copolymers.4,7-9 A wide variety of
ordered morphologies of ABC miktoarm star terpoly-
mers have been found using Monte Carlo simula-
tions.10,11 These include lamellar + sphere, polygonal
cylinders, perforated layer, lamella + cylinder, columnar
piled disk, and lamella in sphere. However, only a few
experimental studies have been reported due to the
difficulties in the synthesis.1-9,12-18
Several methods have been used to synthesize ABC
star terpolymers. The first one is the chlorosilane
approach.1,2,5 3-Miktoarm star terpolymers consisting
of polyisoprene, polystyrene (PS), and polybutadiene
were prepared using step-by-step substitutions of the
chlorine atoms in trichloromethylsilane with living
anionic polymers.1,2 To overcome the difficulties in the
incorporation of polymethacrylates by this method,
Sioula et al. first coupled a living polyisoprene chain
and a living polystyrene chain with trichloromethylsi-
lane and then converted the third SiCl group to a
sterically hindered anionic species, diphenylalkyl anion,
followed by the polymerization of a methacrylate to form
the third arm.3 These polymers have been used in the
morphology studies, and intriguing ordered phases have
been discovered.4,8 The second method is based on the
Other methods were also developed. To avoid the
steric hindrance in the reactions between two polymeric
species as in the first two methods, Lambert and co-
workers developed a synthetic route with two successive
initiation steps from a bifunctional macroinitiator,
which was obtained by end-capping a living polymer
with a difunctional small molecule, 1,1-diphenylethylene
derivative.15,16 Feng and Pan incorporated an atom
transfer radical polymerization (ATRP) initiator into the
junction of a diblock copolymer which was prepared by
controlled cationic ring-opening polymerizations and
synthesized the third arm by ATRP.17 They also incor-
porated a maleic anhydride moiety into the junction of
the diblock copolymer prepared by reversible addition-
fragmentation chain transfer processes and obtained
star terpolymers by reaction of the maleic anhydride
moiety with poly(ethylene glycol).18
Here we report a new method to synthesize ABC
3-miktoarm star terpolymers. A trifunctional initiator
bearing a hydroxy group, an ATRP initiator, and a
nitroxide-mediated radical polymerization (NMRP) ini-
tiator was designed and used in the preparation of star
terpolymers composed of poly(ꢀ-caprolactone) (PCL),
PMMA, and PS arms by sequential living ring-opening
polymerization (ROP) of ꢀ-caprolactone (CL), ATRP of
MMA, and NMRP of styrene (Scheme 1). This approach
is based on the recent progress in controlled/“living”
polymerization techniques. A variety of diblock copoly-
mers have been successfully synthesized from asym-
metric difunctional initiators by combining either ATRP
* To whom correspondence should be addressed. E-mail: zhao@
novell.chem.utk.edu.
10.1021/ma036010c CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/09/2004

Macromolecules, Vol. 37, No. 9, 2004
ABC 3-Miktoarm Star Terpolymers 3129
Sch em e 1. Syn th esis of Sta r Ter p olym er s by
Com bin in g Rin g-Op en in g P olym er iza tion (ROP ),
Atom Tr a n sfer Ra d ica l P olym er iza tion (ATRP ), a n d
Nitr oxid e-Med ia ted Ra d ica l P olym er iza tion (NMRP )
fr om a Tr ifu n ction a l In itia tor
ene glycol 2 and 1 catalyzed by NaH afforded 3, which
was then reacted with 2-bromo-2-methylpropionyl bro-
mide to incorporate the moiety of an ATRP initiator.
Removing THP using dry Amberlyst 15 acidic resin
produced the trifunctional initiator 5. The structure was
1
confirmed by the H NMR spectrum shown in Figure 1,
13C NMR, and mass spectroscopy. This compound was
then used for the synthesis of ABC star terpolymers.
Syn th esis of ABC 3-Mik toa r m Sta r Ter p olym er s
Com p osed of P CL, P MMA, a n d P S Ar m s. Although
the first arm can be synthesized from the trifunctional
initiator using any one of the three polymerization
methods, we synthesized PCL first by living ROP of CL
using triethylaluminum as catalyst because it is much
easier to dry a small molecule than a macroinitiator.
Rigorously anhydrous conditions are required to achieve
a living polymerization of CL.31-35 Considering that the
activation of an ATRP initiator is a bimolecular process
and the free radicals in NMRP are generated by thermal
decomposition which is a unimolecular process, we syn-
thesized the second arm by ATRP of MMA using PCL
macroinitiator and NMRP of styrene to grow the third
arm to minimize the possible steric hindrance encoun-
tered in the initiation of the third polymer chain. We
confirmed that the NMRP initiator was stable at 75 °C
under the typical ATRP conditions.37,38 In a control
experiment for the synthesis of mixed PMMA/PS brushes
on silicon wafers,38 we exposed a pure ATRP initiator-
terminated SAM and a mixed SAM prepared from a
toluene solution that contained an ATRP-initiator-ter-
minated trichlorosilane and a NMRP initiator-termi-
nated trichlorosilane with a molar ratio of 54.4:45.6 to
the same NMRP conditions. A ∼2.0 nm PS film was
observed on the pure ATRP initiator-terminated SAM,
while a 19.1 nm PS brush was found on the mixed SAM.
Presumably, the C-Br bond in the ATRP initiator was
weak and acted as a chain transfer agent in NMRP. To
eliminate the possibility of halogen atom-capped PMMA
chains acting as a chain transfer agent in NMRP, we
used tri(n-butyl)tin hydride to remove the halogen
atoms from the PMMA chain ends in situ after ATRP.38,39
and NMRP,19,20 or NMRP and ROP,21-26 or ATRP and
ROP.21-24,27-30 While the synthesis of diblock copoly-
mers by ATRP and NMRP which are activated at
different temperatures is a two-step process, the two
polymerizations in the other methods can be carried out
simultaneously in one pot.
Resu lts a n d Discu ssion
Design a n d Syn th esis of a Tr ifu n ction a l In itia -
tor . Trifunctional initiator 5 bearing a hydroxy group,
an ATRP initiator, and a NMRP initiator has been
designed for the synthesis of ABC star terpolymers by
combining living ROP, ATRP, and NMRP techniques.
Living ROPs of CL are achieved using alcohols and
triethylaluminum as initiation systems under strictly
anhydrous conditions, producing polymers with narrow
molecular weight distributions and predictable molec-
ular weights.31-35 ATRP and NMRP are two different
controlled/“living” radical polymerization techniques
and have been widely used in recent years in the
synthesis of polymers with narrow polydispersities,
controlled molecular weights, and various architec-
tures.22,36 In previous publications, we used ATRP and
NMRP to fabricate mixed homopolymer brushes on
silicon wafers by “grafting from” either mixed initiator-
terminated self-assembled monolayers (SAMs)37 or asym-
metric difunctional initiator-terminated SAMs.38 Tri-
functional initiator 5, 2-(4-(2′-oxa-4′-hydroxybutyl)phenyl)-
2-(2′′,2′′,6′′,6′′-tetramethyl-1-piperidinyloxy)ethyl 2-bromo-
2-methylpropionate, was prepared via a four-step
procedure as illustrated in Scheme 2. 4-Vinylbenzyl
chloride reacted with free radicals generated from
benzoyl peroxide at 80 °C in the presence of 2,2,6,6-
tetramethylpiperidinooxy produced 1 in a yield of
10.1%.25,38 The reaction between THP-protected ethyl-
ROP of CL In itia ted fr om th e Tr ifu n ction a l In i-
tia tor 5 in Tolu en e. As the first step in the synthesis
of ABC 3-miktoarm star terpolymers composed of PCL,
PMMA, and PS arms, ROP of CL was initiated from
the trifunctional initiator 5 using triethylaluminum as
catalyst in toluene at room temperature under a nitro-
gen atmosphere. Initiator 5 was first dried by azeotropic
distillation using dry toluene at room temperature three
times and further treated with a high vacuum at 35 °C
for 8 h to completely remove any possible water followed
by addition of 1.05 equiv of triethylaluminum via a
syringe. The hydroxy group of the initiator 5 reacted
with triethylaluminum, producing diethylaluminum
monoalkoxide 6 (Scheme 3), which then initiated the
polymerization via a “coordination-insertion” mechan-
ism.31-35 According to this proposed mechanism, the
monomer is inserted into the aluminum-alkoxide bond
with cleavage of the acyl-oxygen bond such that the
binding of the growing chain to the aluminum through
an alkoxide link is maintained. The polymerization was
1
monitored by H NMR spectroscopy, and the monomer
conversion was determined by use of the peak at 4.03
ppm (the ester methylene group in the polymer) and
the peak at 4.25 ppm (the methylene group in -COO-
CH2- in the monomer). The polymers were then puri-
1
fied and analyzed by GPC and H NMR spectroscopy.

3130 He et al.
Macromolecules, Vol. 37, No. 9, 2004
Sch em e 2. Syn th esis of Tr ifu n ction a l In itia tor 5
To confirm that the polymerization of CL initiated
from 6 is a living process, ln([M]0/[M]) vs time was
plotted and shown in Figure 3. A linear relationship
indicated that the polymerization was a first-order
reaction with respect to the monomer concentration, and
the number of the active growing chain ends was
constant during the polymerization. Figure 4 shows the
1H NMR spectrum of sample C-3 in Table 1. Besides
the peaks from PCL, the peaks from the residual
initiator moiety are clearly seen in the magnified area.
The peaks located at 4.53 ppm corresponded to three
protons of the initiator moiety as in the 1H NMR
spectrum of trifunctional initiator 5stwo from the
benzyl group and one from -COOCHH-. Using these
peaks and the ester methylene peaks of PCL located at
4.03 ppm, we calculated the number-average molecular
weights of PCL; the results are summarized in Table 1.
These values are reasonably close to those calculated
on the basis of the ratio of the monomer to the initiator
and the conversion. For instance, the Mn of sample C-1
determined using the peaks at 4.53 ppm as reference is
19 600, very close to 20 200 that was obtained on the
basis of the conversion. This agreement suggested that
the average number of active alkoxy groups per alumi-
num molecule was close to 1 under our experimental
conditions, consistent with the report of Dubois and co-
workers.35 The molecular weights obtained by GPC
analysis relative to polystyrene standards were much
F igu r e 1. 1H NMR spectrum of trifunctional initiator 5.
The reaction conditions and the results are summarized
in Table 1.
As shown in Table 1, the polymers obtained from the
polymerizations that were stopped at conversions less
than 100% exhibited relatively narrow polydispersities.
These results are consistent with those reported in the
literature using other alcohols and Et3Al to polymerize
CL.31 A typical GPC curve (sample C-3 in Table 1) is
shown in Figure 2 (curve a). As reported by Dubois et
al.,35 the molecular weight distributions broadened
significantly when the polymerization time exceeded the
time required for a complete monomer conversion. For
instance, the polydispersity of sample C-4 in Table 1,
which was isolated after 100% conversion, was 1.82,
though a single peak was observed in GPC analysis.
This is likely due to the intra- and intermolecular
transesterification reactions promoted by the aluminum
alkoxide catalyst.
1
higher than those obtained from H NMR analysis and
the calculation based on the conversion.
ATRP of MMA Usin g P CL Ma cr oin itia tor . ATRP
of MMA was then initiated from the PCL macroinitiator
in anisole using pentamethyldiethylenetriamine (PM-
DETA) and CuCl as catalytic system to synthesize the
1
second arm. The polymerization was monitored by H

Macromolecules, Vol. 37, No. 9, 2004
ABC 3-Miktoarm Star Terpolymers 3131
Sch em e 3. Rin g-Op en in g P olym er iza tion of E-Ca p r ola cton e Usin g In itia tor 5 a n d AlEt3
Ta ble 1. P olym er iza tion Con d ition s a n d Resu lts of
Rin g-Op en in g P olym er iza tion of E-Ca p r ola cton e Usin g
Tr ifu n ction a l In itia tor 5 a n d Et3Al a s th e In itia tion
System in Tolu en e a t Room Tem p er a tu r e u n d er a N2
Atm osp h er e
b
c
d
sample [M]0/[I]0 conv (%)a Mn,cal
Mn,NMR Mn,GPC PDIe
C-1
C-2
C-3
C-4
200
217
135
150
88.7
64.5
60.2
20 200 19 600
16 000 18 100
9 300 11 400
17 100 NA
48 400 1.35
39 700 1.37
26 800 1.34
41 800 1.82
100
a
Determined from 1H NMR spectrum using the ester methylene
b
peaks of poly(ꢀ-caprolactone) (PCL) and ꢀ-caprolactone. Calcu-
lated by the ratio of the monomer to the initiator and the
conversion. c Calculated from 1H NMR spectrum of PCL. Mn,NMR
) (I4.03/2)/(I4.53/3) × 114.1, where I4.03 and I4.53 were integral values
of the peaks located at 4.03 ppm (the ester methylene group of
PCL, 2H) and 4.53 ppm (from the residual initiator moiety, 3H).
d
Determined by GPC using PS standards. e PDI ) polydispersity
F igu r e 3. Relationship between ln([M]0/[M]) and the poly-
merization time in the ring-opening polymerization of ꢀ-ca-
prolactone using trifunctional initiator 5 and Et3Al as the
initiation system in toluene at room temperature. [M]0/[I]0 )
135; [I]0:[AlEt3]0 ) 1:1.05.
index. Determined by GPC.
F igu r e 2. GPC curves of (a) a poly(ꢀ-caprolactone) (C-3 in
Table 1), (b) a poly(ꢀ-caprolactone)-b-poly(methyl methacrylate)
(CM-3 in Table 2), and (c) a star terpolymer (CMS-3 in Table
2).
F igu r e 4. 1H NMR spectrum of a poly(ꢀ-caprolactone) (sample
C-3 in Table 1).
NMR using the peaks located at 6.90-7.00 ppm, which
belonged to the solvent anisole as the internal standard.
The monomer conversion was determined by using the
integral value of the peak located at 6.07 ppm (1H from
the double bond of the monomer) at time t and the value
of the same peak at time t ) 0. After a desired
conversion was reached, excess tri(n-butyl)tin hydride
with respect to the initiator was injected into the
mixture to remove the halogen atoms from the PMMA
chain ends in situ. The polymerization conditions and
the results of 1H NMR and GPC analysis are sum-
marized in Table 2. A typical GPC curve (CM-3 in Table
2) is shown in Figure 2 (curve b). The polydispersities
of the diblock copolymers remained relatively low, less
than 1.30. The peak shifted to a higher molecular weight
compared to that of the PCL macroinitiator, and no
shoulder peak was observed. Figure 5 shows the kinetic
data of ATRP of MMA. An almost linear relationship
between ln([M]0/[M]) and the reaction time suggests that
the polymerization of MMA was controlled. A typical
1H NMR spectrum of a diblock copolymer PCL-b-PMMA
(CM-3 in Table 2) is shown in Figure 6. Using the peaks
at 4.03 ppm (the ester methylene group of PCL) and
the peak at 3.57 ppm (the ester methyl group of PMMA),
the number-average molecular weight of PMMA were
calculated and included in Table 2. These values are
close to those calculated on the basis of the conversion

3132 He et al.
Macromolecules, Vol. 37, No. 9, 2004
Ta ble 2. Rea ction Con d ition s a n d th e Resu lts of Atom Tr a n sfer Ra d ica l P olym er iza tion (ATRP ) of Meth yl Meth a cr yla te
(MMA) Usin g P oly(E-ca p r ola cton e) (P CL) Ma cr oin itia tor s a n d Nitr oxid e-Med ia ted Ra d ica l P olym er iza tion (NMRP ) of
Styr en e Usin g P CL-b-P MMA Ma cr oin itia tor sa
d
e
g
method
sample
initiatorb
[M]0/[I]0
conv (%)c
Mn,cal
Mn,NMR
CL:MMA:Stf
Mn,GPC
PDIg
ATRP
NMRP
ATRP
NMRP
ATRP
NMRP
CM-1
CMS-1
CM-2
CMS-2
CM-3
CMS-3
C-1
CM-1
C-2
CM-2
C-3
CM-3
503/1
991/1
755/1
1106/1
605/1
957/1
22.2
11.4
27.1
19.6
21.2
12.1
11 200
11 800
20 500
22 600
12 800
12 000
11 300
10 900
19 900
23 600
9 600
72 600
77 000
63 100
69 200
46 100
49 700
1.22
1.25
1.27
1.35
1.26
1.31
172:113:105
159:199:227
100:96:131
13 600
a
ATRPs of MMA were carried out at 75 °C under a N2 atmosphere using PCL macroinitiators; NMRPs of styrene were carried out at
120 °C under a nitrogen atmosphere using PCL-b-PMMA macroinitiators. Initiators C-1, C-2, and C-3 were from Table 1. c Conversions
b
were determined by 1H NMR spectroscopy using either the peaks of the solvent (in ATRP of MMA) or the ester methylene peaks of PCL
d
as internal standard (in NMRP of styrene). The number-average molecular weights of the new arm calculated from the ratio of the
monomer to the initiator [M]0/[I]0 and the conversion. e The number-average molecular weights of the new arm calculated using PCL as
reference. f The degrees of polymerizations of PCL:PMMA:PS calculated from 1H NMR spectra. The number-average molecular weight
g
(Mn) and polydispersity index (PDI) of diblock copolymers or star terpolymers determined by GPC using PS standards.
F igu r e 5. Relationship between ln([M]0/[M]) and the poly-
F igu r e 7. Relationship between ln([M]0/[M]) and the poly-
merization time for atom transfer radical polymerization of
merization time for nitroxide-mediated radical polymerization
methyl methacrylate using poly(ꢀ-caprolactone) macroinitiator
of styrene using a poly(ꢀ-caprolactone)-b-poly(methyl meth-
in anisole at 75 °C. [M]0/[I]0 ) 605/1; [I]0:[CuCl]0:[pentameth-
yldiethylenetriamine]0 ) 0.8:1:2.
acrylate) macroinitiator in chlorobenzene at 120 °C. [M]0/[I]0
) 957/1.
polymerization was stopped at monomer conversions
less than 20% to avoid the gel effect. During the
polymerization, samples were taken from the reaction
mixture at a desired time via a syringe for 1H NMR
analysis. Using the peak at 4.03 ppm (the methylene
group of -COOCH2- in PCL) as the internal standard,
the conversion was determined by comparing the inte-
gral value of the peaks at 5.72 ppm to that of the same
peaks in the original sample. The polymerization condi-
tions and the results of 1H NMR spectroscopy and GPC
analysis are summarized in Table 2. GPC analysis (see
Figure 2c) showed a single peak shifting to a higher
molecular weight compared to that of the diblock
copolymer macroinitiator, and the polydispersity re-
mained relatively low. Kinetic analysis showed an
almost linear relationship between ln([M]0/[M]) and the
reaction time (Figure 7), suggesting that the polymer-
izations were controlled and the concentration of the
F igu r e 6. 1H NMR spectrum of a poly(ꢀ-caprolactone)-b-poly-
(methyl methacrylate) (CM-3 in Table 2).
and the ratio of the monomer to the macroinitiator. For
instance, the calculated Mn of PMMA arm based on the
conversion for sample CM-2 in Table 2 is 20 500, while
1
growing chains was a constant. Figure 8 shows the H
1
the value calculated by H NMR using the ester meth-
NMR spectrum of a star terpolymer (CMS-3 in Table
2). The peaks in the range 6.25-7.21 ppm belong to the
aromatic protons of PS. The molecular weights of PS
calculated using these peaks and the ester methylene
peaks of PCL are close to those calculated on the basis
of the monomer conversion and the ratio of the monomer
to the initiator. For example, the Mn of PS in sample
CMS-1 determined using PCL as reference is 10 900,
very close to 11 800 obtained on the basis of the
conversion. The increases in Mn of star terpolymers
ylene peak of PCL as reference is 19 900. However,
there was a large discrepancy between these two values
if the reaction mixture was very viscous, leading to a
gel effect.
NMRP of Styr en e Usin g P CL-b-P MMA Ma cr o-
in itia tor . To synthesize the third-arm PS, NMRPs of
styrene were carried out using PCL-b-PMMA macro-
initiators in chlorobenzene at 120 °C. A ratio of the
monomer to the initiator of ∼1000 was used, and the

Macromolecules, Vol. 37, No. 9, 2004
ABC 3-Miktoarm Star Terpolymers 3133
F igu r e 8. 1H NMR spectrum of a star terpolymer composed
of poly(ꢀ-caprolactone), poly(methyl methacrylate), and poly-
styrene arms (CMS-3 in Table 2).
F igu r e 9. GPC analysis of the polymers obtained in arm
cleavage experiments: (a) a star terpolymer (CMS-2); (b) the
polymer obtained after reaction for 4 h; (c) poly(methyl
methacrylate) obtained after reaction for 4 days and removal
of polystyrene by extraction with cyclohexane for 3 h; (d)
polystyrene obtained after reaction for 4 days and extraction
with cyclohexane for 3 h.
relative to the macroinitiators obtained by GPC are
much lower than those calculated from 1H NMR and
the conversion. The compact structure of the star
terpolymers should be responsible for this. To confirm
that the PS chains were connected to the PCL-b-PMMA
macroinitiator, we used cyclohexane to extract star
terpolymer CMS-3 in a Soxhlet extractor. No homopoly-
was cleaved after reaction for 4 h was unknown, GPC
analysis indicated a very high percentage of PS-b-
PMMA was maintained after 4 h reaction. The number-
average molecular weight of PS-b-PMMA was 46 000
with a polydispersity of 1.29, close to the sum of the
molecular weights of PS and PMMA (Mn ) 50 100, GPC
results) obtained after the complete cleavage. Arm
cleavage experiments confirmed the structure of star
terpolymers that were synthesized by this new method.
1
mer of styrene was found in cyclohexane, and the H
NMR spectrum showed no changes in the ratios of PS
to PCL and PMMA, indicating that the polystyrene
chains were grown from the junction points of PCL-b-
PMMA.
Ar m Clea va ge of a Sta r Ter p olym er (CMS-2). To
further confirm the structure of ABC 3-miktoarm star
terpolymers that were synthesized by this method, we
cleaved the arms off the star terpolymer CMS-2 using
sodium methoxide in a mixed solvent of THF and
methanol.40,41 Sodium methoxide was chosen in order
to keep the ester group of PMMA intact but to cleave
other ester bonds. It was observed in the experiments
that the ester groups of PCL were cleaved much faster
than the ester linkage between PMMA and PS arms,
Con clu sion s
ABC star terpolymers composed of PCL, PMMA, and
PS arms were successfully synthesized from a trifunc-
tional initiator using living ROP of CL, ATRP of MMA,
and NMRP of styrene in a three-step process. GPC and
kinetic analysis demonstrated that all three types of
polymerization were controlled, leading to relatively low
polydispersities. The structure of ABC star terpolymers
was further confirmed by cleavage of arms off a star
terpolymer. This strategy can be extended to the
synthesis of a variety of star terpolymers with controlled
molecular weights and low molecular weight distribu-
tions as living ROP can be extended to the monomer
lactide and ATRP can be applied to a variety of meth-
acrylates and acrylates, providing a great flexibility in
tailoring the compositions and the molecular weights
of star terpolymers.
1
which was originally from trifunctional initiator 5. H
NMR spectroscopy was used to determine the minimum
reaction time that was required to completely degrade
PCL chain. Under the conditions described in Experi-
mental Section, it took ∼4 h to completely degrade PCL
chain. A portion of the reaction mixture was then taken
for GPC analysis (curve b Figure 9), and the rest of the
mixture was continued refluxing for 4 days to completely
cleave the ester bond between PS arm and PMMA arm.
The resultant mixture of PS and PMMA was separated
by extraction with cyclohexane. 1H NMR spectra showed
that a complete separation of PS and PMMA was
achieved after extraction with cyclohexane for 3 h and
100% pure PS and PMMA were obtained. GPC analysis
Exp er im en ta l Section
Ma ter ia ls a n d Ch a r a cter iza tion . 4-Vinylbenzyl chloride
(90%, Acros), 2,2,6,6-tetramethylpiperidinooxy (TEMPO, 98%,
Acros), benzoyl peroxide (BPO, 97%, Aldrich), and sodium
hydride (NaH, 60% dispersion in mineral oil, Acros) were used
as received. ꢀ-Caprolactone (99%, Aldrich), methyl methacryl-
ate (99%, Acros), and styrene (99%, Aldrich) were dried with
calcium hydride and distilled under reduced pressure before
use. Toluene and tetrahydrofuran (THF) were distilled from
sodium and benzophenone under nitrogen atmosphere just
prior to use. Triethylaluminum (1.9 M solution in toluene) was
purchased from Aldrich and used as received. All other
chemical reagents were purchased from either Acros or Aldrich
and used without further purification.
showed that the molecular weight of PS arm (Mn
)
23 800, curve d in Figure 9) was close to the value
determined from the 1H NMR analysis (22 600 based
on the conversion and 23 600 based on the peaks of
PCL), and the polydispersity was 1.34. The molecular
weight of PMMA obtained by GPC analysis (Mn
)
26 300, Mw/Mn ) 1.29, curve c in Figure 9) was also close
to that of PMMA (Mn ) 28 300, Mw/Mn ) 1.26) obtained
by cleavage of the PCL-b-PMMA macroinitiator. Since
PS standards were used for calibration, there was a
discrepancy between the values obtained by GPC and
1H NMR analysis (Mn ) 19 900). Although the percent-
age of the ester bond between PS and PMMA arms that
The 1H and 13C NMR spectra were recorded on a Varian
Mercury 300 MHz NMR spectrometer using CDCl3 as the
solvent and the residual solvent proton as the internal
standard. Mass spectroscopy was performed in the Mass

3134 He et al.
Macromolecules, Vol. 37, No. 9, 2004
Spectroscopy Center in the Chemistry Department at the
University of Tennessee at Knoxville on a Micromass Quattro
II tandem electrospray spectrometer run in the positive ion
electrospray mode. Gel permeation chromatography (GPC) was
carried out at room temperature using a modular Knauer GPC
system with a HPLC K-501 pump, a UV-K2501 detector, a RI-
K2301 refractive index detector, and 5 µm PSS-SDV gel, 102-
105 Å 60 cm, and 100 Å 60 cm columns. The data were
processed using Polymer Standards Service software (PSS
WinGPC). Tetrahydrofuran (THF) was used as the carrier
solvent at a flow rate of 1.0 mL/min, and toluene was used as
internal standard. Standard monodisperse polystyrenes (Poly-
mer Laboratories) were used for calibration.
Syn th esis of 1. Benzoyl peroxide (5.0 g, 21 mmol) and
4-vinylbenzyl chloride (47.3 g, 0.31 mol) were added into a 250
mL three-necked flask. The mixture was stirred under N2
atmosphere in an ice bath, and 2,2,6,6-tetramethylpiperidinoxy
(TEMPO, 9.07 g, 58.2 mmol) was added slowly. The flask was
then placed in an oil bath with a preset temperature of 80 °C.
After the reaction proceeded for 20 h, excess 4-vinylbenzyl
chloride was removed under reduced pressure, and the crude
product was purified by column chromatography using a
mixture of methylene chloride and hexanes with a volume ratio
of 3:1 as eluent to give 1 (1.81 g, 10.1%). 1H NMR δ (ppm):
0.74, 1.04, 1.17, 1.33 (each br s, 12H, CH3), 1.26-1.56 (m, 6H,
-CH2CH2CH2-), 4.49 (dd, 1H, -OCHH-), 4.56 (s, 2H, -CH2-
Cl), 4.79 (dd, 1H, -COOCHH-), 5.03 (dd, 1H, -CH-), 7.35-
7.71 (complex m, 7H, ArH), 7.87-7.91 (m, 2H, ArH). 13C NMR
δ (ppm): 15.09, 20.37, 34.06, 40.35, 46.08, 60.11, 66.61, 83.55,
127.86, 128.29, 128.30, 129.52, 130.07, 132.86, 136.67, 140.96,
166.26. Mass spectrum 430.14.
Syn th esis of 2. Ethylene glycol (148.0 g, 2.387 mol), 3,4-
dihydro-2H-pyran (10.0 g, 0.119 mol), and tetrahydrofuran (20
mL) were added into a 250 mL flask. After the mixture was
stirred in an ice bath for 15 min, 2 drops of concentrated HCl
were added. The reaction proceeded at room temperature for
15 h. After removal of THF by rotavapor, methylene chloride
(50 mL) was added. The mixture was washed with water five
times (5 × 30 mL) and then dried with anhydrous sodium
sulfate. After removal of methylene chloride by rotavapor, the
crude product was distilled under reduced pressure to give 2
as a colorless liquid (13.98 g, 81.0%). 1H NMR δ (ppm): 1.42-
1.82 (m, 6H, -CHCH2CH2CH2-), 2.95 (s, 1H, -OH), 3.42-
3.51 (m, 1H, -OCHHCH2CH2-), 3.61-3.76 (m, 4H, -OCH2C-
H2O-), 3.81-3.92 (m, 1H, -OCHHCH2CH2-), 4.51 (m, 1H,
-OCHO-). 13C NMR δ (ppm): 19.85, 25.12, 30.66, 62.09,
63.09, 70.56, 99.98.
Syn th esis of 3. Dry THF (20 mL), 2 (3.72 g, 25.5 mmol),
and NaH (1.54 g, 38.5 mmol) were added into a 100 mL three-
necked flask. The mixture was stirred under a nitrogen
atmosphere for 30 min followed by the addition of a solution
of 1 (2.2 g, 5.1 mmol) in THF (10 mL) in a dropwise fashion.
The mixture was stirred at room temperature overnight. The
solvent was removed by a rotavapor, and the residue was
partitioned between water (20 mL) and methylene chloride (20
mL). The aqueous phase was neutralized by a 2 N HCl solution
and was extracted by methylene chloride (3 × 20 mL). The
organic extracts were combined and dried over anhydrous
sodium sulfate. After the removal of methylene chloride by a
rotavapor, the crude product was purified by column chroma-
tography using hexanes/ethyl acetate (1:1, v/v) as eluent to
afford 3 (1.71 g, 76.8%). 1H NMR δ (ppm): 1.12, 1.19, 1.31,
1.47 (each br s, 12H, -CH3) 1.32-1.84 (m, 12H, -CHCH2CH2-
CH2- and -CCH2CH2CH2C-), 3.45-3.49 (m, 1H, -OCHHCH2-
CH2-), 3.59-3.70 (m, 4H, HOCHHCHON and -OCH2CHHO-
), 3.81-3.89 (m, 2H, -OCHHCH2CH2- and -OCH2CHHO-
), 4.18 (dd, 1H, HOCHH-), 4.55 (s, 2H, ArCH2O-), 4.62 (t, 1H,
-OCHO-), 5.27 (dd, 1H, -HOCH2CH-), 5.83 (br s, 1H, -OH),
7.31 (m, 4H, ArH). 13C NMR δ (ppm): 17.08, 19.41, 20.34,
20.66, 25.39, 30.52, 32.69, 34.57, 40.13, 40.33, 60.31, 61.65,
62.16, 66.63, 69.37, 69.65, 72.82, 83.36, 98.87, 126.78, 127.65,
138.07, 138.14.
by addition of a solution of 2-bromo-2-methylpropionyl bromide
(3.83 g, 15.6 mmol) in methylene chloride (10 mL) in a
dropwise fashion. The reaction mixture was stirred at room
temperature for 8 h, then washed with water (4 × 20 mL),
and dried over anhydrous sodium sulfate. After the removal
of methylene chloride using a rotavapor, the crude product was
purified by column chromatography with 8:1 hexanes/ethyl
acetate as eluent to afford 4 (1.81 g, 79.2%). 1H NMR δ (ppm):
0.72, 1.00, 1.16, 1.30 (each br s, 12H, -CH3), 1.22-1.84 (m,
12H, -CCH2CH2CH2C- and -CHCH2CH2CH2-), 1.75 (s, 6H,
CH3-CBr-CH3), 3.44-3.50 (m, 1H, -OCHHCH2CH2-), 3.57-
3.63 (m, 3H, -OCH2CHHO-), 3.80-3.89 (m, 2H, -OCH2-
CHHO- and -OCHHCH2CH2-), 4.40 (dd, 1H, -COOCHH-
CHON), 4.53-4.63 (m, 4H, -OCHO-, ArCH2O-, and -COOC-
HHCHON), 4.93 (dd, 1H, -CHON), 7.28 (m, 4H, ArH). 13C
NMR δ (ppm): 17.07, 19.40, 20.34, 25.39, 30.52, 30.68, 33.98,
40.30, 55.55, 60.11, 62.11, 66.57, 67.48, 69.26, 72.87, 83.29,
98.81, 127.27, 127.56, 137.66, 139.49, 171.31. Mass spectrum:
584.3.
Syn th esis of 2-(4-(2′-Oxa -4′-h yd r oxybu tyl)p h en yl)-2-
(2′′,2′′,6′′,6′′-tetr a m eth yl-1-p ip er id in yloxy)eth yl 2-Br om o-
2-m eth ylp r op ion a te (5). Compound 4 (1.80 g, 3.1 mmol), dry
Amberlyst 15 ion-exchange resin (0.60 g), and methanol (10
mL) were added into a 50 mL flask. The mixture was stirred
under N2 at 35 °C overnight. The Amberlyst 15 resin was
filtered off, and the solvent was removed by a rotavapor. The
crude product was purified by column chromatography with
2:1 hexanes/ethyl acetate as eluent to give 5 (1.02 g, 65.8%).
1H NMR δ (ppm): 0.73, 1.02, 1.17, 1.30 (each br s, 12H, -CH3),
1.21-1.54 (m, 6H, -CH2CH2CH2-), 1.76 (s, 6H, CH3-CBr-
CH3), 2.10 (t, 1H, -OH), 3.54-3.57 (m, 2H, -OCH2CH2OH),
3.71-3.76 (m, 2H, -OCH2CH2OH), 4.42 (dd, 1H, -COOCHH-
), 4.53-4.59 (m, 3H, ArCH2O- and -COOCHH-), 4.95 (dd,
1H, -CHON), 7.24-7.33 (m, 4H, ArH). 13C NMR δ (ppm):
17.07, 20.35, 30.69, 34.05, 55.55, 60.14, 61.84, 67.48, 71.27,
73.02, 83.25, 127.39, 127.68, 137.79, 171.32. Mass spectrum:
500.2.
ROP of CL fr om Tr ifu n ction a l In itia tor 5. A typical
procedure for ROP of CL is as follows. Trifunctional initiator
5 (0.105 g, 0.21 mmol) was added into a dry 25 mL two-necked
flask followed by capping of the flask with a rubber septum.
The flask was then degassed and back-filled with nitrogen
three times followed by injection of dry toluene (2.0 mL) via a
syringe. After the initiator was dissolved, a high vacuum was
used to remove toluene at room temperature. This process was
repeated two more times. The flask was then placed in an oil
bath at 35 °C and evacuated for 8 h. The flask was then
removed from the oil bath and filled with nitrogen. Dry toluene
(3.0 mL) was added followed by injection of the solution of
triethylaluminum in toluene (0.116 mL of 1.9 M solution, 0.22
mmol) via a syringe under a nitrogen atmosphere. (Caution:
the solution of triethylaluminum in toluene should be handled
with great care as it can catch fire in air.) The mixture was
stirred under a N2 atmosphere at room temperature for 2 h,
and then dry toluene (7.0 mL) and CL (3.0 mL, 28 mmol) were
injected via syringes. Samples were taken from the reaction
mixture via syringes at a desired time interval for 1H NMR
analysis. The polymerization was stopped at a conversion of
60.2% by addition of excess glacial acetic acid with respect to
the aluminum catalyst (0.2 mL). The reaction mixture was
diluted with methylene chloride, passed through a short
neutral aluminum oxide column, and precipitated in methanol.
The polymer was purified by precipitation in methanol three
times followed by treatment with a high vacuum to give a dry
polymer (1.55 g, 50.2%). The polymer was analyzed by GPC
relative to PS standards. Mn ) 26 800; Mw/Mn ) 1.34.
ATRP of MMA Usin g P CL Ma cr oin itia tor . A typical
procedure for ATRP of MMA is as follows. Anisole (14.80 g)
and MMA (4.78 g, 47.8 mmol) were added into a flask
containing a PCL macroinitiator (0.90 g, 0.079 mmol). After
PCL was completely dissolved, CuCl (10.0 mg, 0.101 mmol)
and pentamethyldiethylenetriamine (34.2 mg, 0.198 mmol)
were added. The mixture was degassed by freeze-pump-thaw
for three times and then placed in an oil bath with a preset
temperature of 75 °C. By use of the peaks at 6.90-7.00 ppm,
Syn th esis of 4. Methylene chloride (15 mL), 3 (1.70 g, 3.91
mmol), and triethylamine (2.40 g, 23.8 mmol) were added into
a flask. The reactor was then placed in an ice bath followed

Macromolecules, Vol. 37, No. 9, 2004
ABC 3-Miktoarm Star Terpolymers 3135
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J .; Disko, M. M.; Garner, R. T.; Liang, K. S.; Lohse, D. J .;
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which belonged to the solvent anisole as the internal standard,
the conversion of the monomer was determined by 1H NMR
analysis of the sample taken at a desired time interval using
the peak located at 6.07 ppm, which was assigned to one proton
in the double bond of MMA. After polymerization for 280 min,
tri(n-butyl)tin hydride (0.18 mL, 0.67 mmol) was injected, and
the reaction continued for 30 min. The mixture was then
opened to air and cooled to room temperature. The catalyst
was removed by passing the polymer solution through a short
aluminum oxide column. The crude polymer was purified by
precipitation in methanol three times and dried under high
vacuum (1.53 g, 13.2%). The block copolymer was analyzed
by GPC against PS standards. Mn ) 46 100; Mw/Mn ) 1.26.
1H NMR analysis showed that the ratio of degrees of poly-
merization of PCL and PMMA was 1:0.96.
NMRP of Styr en e Usin g th e Block Cop olym er P CL-
b-P MMA Ma cr oin itia tor . A typical procedure of NMRP of
styrene using a PCL-b-PMMA macroinitiator is as follows.
Chlorobenzene (5.32 g) and styrene (4.48 g, 43.1 mmol) were
added into a flask containing the diblock copolymer macro-
initiator (0.95 g, 0.045 mmol). The mixture was degassed by
three freeze-pump-thaw cycles and then placed in an oil bath
with a preset temperature of 120 °C. During the polymeriza-
tion, samples were taken from the reaction mixture at a
desired time via a syringe for 1H NMR analysis. Using the
peak at 4.03 ppm (the methylene group of -COOCH2- in PCL)
as the internal standard, the conversion was determined by
comparing the integral value of the peaks at 5.72 ppm to that
of the same peaks in the original sample. After polymerization
for 400 min, the mixture was cooled to room temperature and
opened to air. The polymer was purified by precipitation in
methanol for three times. Treatment with a high vacuum gave
a dry polymer (1.13 g, 4.0%). The star copolymer was analyzed
by GPC against PS standards. Mn ) 49 700; Mw/Mn ) 1.31.
1H NMR analysis showed that the ratio of degrees of poly-
merization of PCL and PMMA and PS was 1:0.96:1.31.
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Clea va ge of a P CL-b-P MMA (CM-2). A solution of sodium
methoxide (20.0 mg, 0.37 mmol) in a mixed solvent of THF
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containing a solution of a diblock copolymer PCL-b-PMMA
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Clea va ge of a n ABC Sta r Ter p olym er (CMS-2). A
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refluxed at 70 °C. The degradation of PCL was monitored by
1H NMR. As soon as the peaks at 4.03 ppm completely
disappeared (after ∼4 h), a portion of the reaction mixture (3.0
mL) was taken, and the solvent was removed by a rotavapor.
The polymer was redissolved in methylene chloride and
precipitated in methanol. The rest of the reaction mixture was
refluxed for 4 days. After removal of the solvents, the polymer
was precipitated in methanol, dried with a high vacuum, and
then extracted with cyclohexane using a Soxhlet extractor for
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Ack n ow led gm en t. The authors thank the Univer-
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American Chemical Society Petroleum Research Funds
(PRF# 40084-G7) for supporting this research.
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MA036010C