Versatile Chain Transfer Agents for Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerization to Synthesize Functional Polymeric Architectures

Article abstract of DOI:10.1021/ma035468b

We report the syntheses and uses of versatile chain transfer agents (CTAs) that produce well-controlled macromolecular architectures with specific chain-end functionalities, via reversible addition fragmentation chain transfer (RAFT) polymerization). Exam

Full text of DOI:10.1021/ma035468b

Macromolecules 2004, 37, 2709-2717
2709
Versatile Chain Transfer Agents for Reversible Addition Fragmentation
Chain Transfer (RAFT) Polymerization to Synthesize Functional
Polymeric Architectures
Se´ba stien P er r ier ,* P itta ya Ta k olp u ck d ee, J a m es Westw ood , a n d Da vid M. Lew is
Department of Colour and Polymer Chemistry, University of Leeds, Leeds, LS2 9J T, U.K.
Received September 29, 2003; Revised Manuscript Received J anuary 25, 2004
ABSTRACT: We report the syntheses and uses of versatile chain transfer agents (CTAs) that produce
well-controlled macromolecular architectures with specific chain-end functionalities, via reversible addition
fragmentation chain transfer (RAFT) polymerization). Examples of architectures are given, including
amphiphilic copolymers and block copolymers incorporating a biodegradable block. These CTAs are also
used for the grafting of poly(styrene), poly(methyl methacrylate) and poly(methyl acrylate) from cotton.
Sch em e 1. Gen er a lly Accep ted Rea ction Sch em e for
Rever sible Ad d ition F r a gm en ta tion Ch a in Tr a n sfer
(RAF T) a n d Ma cr om olecu la r Ar ch itectu r e Design via
In ter ch a n ge of Xa n th a te (MADIX) P olym er iza tion s
In tr od u ction
In recent years, polymer chemistry has moved away
from the bulk synthesis of high molecular weight
chemicals and is now targeting the synthesis of specialty
compounds via the introduction of specific functional-
ities on polymer backbones or chain ends. Among the
various polymerization processes that have been re-
ported to achieve such products, living radical polym-
erization appears to be one of the most promising for
high scale applications. The synthesis of functional
polymers with predictable molecular weight and narrow
molecular weight distribution can easily be achieved,
under conditions similar to those of free radical polym-
erization.1 To date, the most important processes are
nitroxide mediated polymerization (NMP), transition
metal mediated living radical polymerization, reversible
addition fragmentation chain transfer (RAFT) polym-
erization, and macromolecular architecture design by
interchange of xanthates (MADIX). NMP is based on
the use of a stable nitroxide radical and, to date, is
limited to few monomers (styrene derivatives, acrylates,
N,N-dimethylacrylamide, acrylonitrile, dienes, and meth-
acrylates as comonomers).2 Transition metal mediated
living radical polymerization3,4 has been proven to
efficiently polymerize a wider range of monomers,
including styrene derivatives, (meth)acrylates, acryloni-
trile, 4-vinylpyridine, and (meth)acrylamide, among
other more specific monomers, in a variety of polymer-
ization conditions.5 An additional feature of this tech-
nique is the possibility to design polymeric chains with
chain-end functionalities. Indeed, Haddleton et al. first
reported the use of molecules bearing a hydroxyl group
that can be transformed into initiators for copper
mediated living radical polymerization.6,7 This leads to
the easy synthesis of block copolymers including blocks
that cannot be formed through free radical polymeri-
zation, polymers showing specific functionalities at their
chain-ends, star polymers, etc. The system is however
limited by the use of a catalyst: pollution of the final
product by the metal and/or ligand present in the
catalyst system is often a major drawback for large-scale
processes.
RAFT8,9 and MADIX10,11 seem so far the two most
promising of the living radical polymerization systems.
A wide range of monomers already successfully polym-
erized, ease of scaleup of the reaction and high tolerance
to functional groups makes them the most suitable
techniques to obtain well-defined polymeric architec-
tures. RAFT and MADIX are based on a similar process
which consist in the simple introduction of a small
amount of dithioester of the generic formula 1, Scheme
1, (chain transfer agent, CTA) in a classic free radical
system (monomer + initiator). The transfer of the CTA
between growing radical chains (Scheme 1), present at
very low concentration, and dormant polymer chains,
present at higher concentration (3 or 4 orders of
magnitude), will regulate the growth of the molecular
weight, and limit the termination reactions.
One of the key steps of the process is the design of
the initial CTA, as the choice of R and Z groups depends
on the monomer to be polymerized. Indeed, as the Z
group influences strongly the stability of the dithioester
radical intermediate, strong stabilizing groups will favor
the formation of the radical intermediate, and therefore
enhance the reactivity of the SdC bond toward radical
addition. However, the stability of the intermediate
needs to be finely tuned, to favor its fragmentation
which will free the reinitiating group (R).12-17 The R
group must be chosen as a good leaving group by
comparison to the growing polymeric chain and a good
reinitiating species toward the monomer used. To a
lesser extent than the Z group, R will also participate
in the stabilization of the radical intermediate. Param-
eters such as the stability of the generated radical, steric
bulk, and polarity need to be considered for the choice
of the R group. Previous studies have shown the
importance of this group when polymerizing monomers
with a high rate of propagation.18-20 To date, cumyl and
cyanoisopropyl groups seem to be the most efficient for
the reinitiation step.21 Another important effect of the
* Corresponding author. Fax: +44 113 343 2947. Telephone:
+44 113 343 2932. E-mail: S.perrier@leeds.ac.uk.
10.1021/ma035468b CCC: $27.50 © 2004 American Chemical Society
Published on Web 03/06/2004

2710 Perrier et al.
Macromolecules, Vol. 37, No. 8, 2004
Ga s Ch r om a togr a p h y)Ma ss Sp ectr om etr y (GC)MS).
GC chromatograms were recorded by Varian Star 3400 CX.
The injection temperature was set at 250 °C. The GC column
is Varian CP-Sil 8 CB low bleed/MS (5% phenylpolysiloxane/
95% methylpolysiloxane), 30 m × 0.25 mm with 0.25 µm
diameter and the temperature was controlled by the program
from 50 to 250 °C with a rate of 10 °C/min. MS patterns were
recorded by Varian Saturn 3 system (ion trap, electron
ionization mode). The MS detector temperature was set at 250
°C.
F TIR a n d Ra m a n Sp ectr oscop y. FTIR spectra were
recorded using a Perkin-Elmer Spectrum One infrared Fourier
transform spectrometer. The contact sampler is a horizontal
internal reflectance accessory (ATR) for most of samples,
unless otherwise stated, with a resolution of 4.00 cm-1. Scan
speed was set at 0.5 cm/s for one hundred scans for ATR. The
scan speed of the KBr disk technique was set at 0.2 cm/s for
16 scans
R group is its use to either introduce chain-end func-
tionalities into polymers or design various polymeric
architectures. This was initially achieved by the CSIRO
group, through the use of a RAFT agent derived from
the free radical initiator 4,4′-azobis(4-cyanopentanoic
acid). This CTA shows a carboxylic acid function that
can easily be reacted with OH groups to form macro-
CTAs, or functional chain transfer agents. Applications
include the use of poly(ethylene glycol)22 or Kraton.23
The drawback of such CTAs is their very demanding
synthetic process which often requires three or four
reaction steps.
In this work, we report the utilization of CTAs with
improved structures (R group with better leaving and
reinitiation ability) to control the living radical polym-
erization of the key monomers that are styrene, methyl
methacrylate, methyl acrylate, and dimethyl acryl-
amide. The synthesis of the CTA is simplified to a one-
step reaction and offers the opportunity to introduce any
molecules bearing a hydroxyl group at the end of the
polymeric chain, as has been previously demonstrated
by transition metal mediated living radical polymeri-
zation. The technique reported here, however, offers
supplementary advantages over transition metal medi-
ated LRP: (a) there is no potential pollution of the end
product by residual catalyst, (b) a wider range of
monomers is available, and (c) the process has great
potential for scaling up reactions. Examples of syntheses
of block copolymers and cotton graft polymers are given.
Raman spectra were monitored using a Perkin-Elmer
system 2000 NIR FT Raman. The laser source is Nd:YAG with
diode pumping. The scan speed was 0.2 cm/s for 16 scans.
Syn t h eses of R ever sib le Ad d it ion F r a gm en t a t ion
Ch a in -Tr a n sfer Agen ts. Syn th esis of S-Meth oxyca r bo-
n ylp h en ylm eth yl Dith ioben zoa te (MCP DB, See Sch em e
3, CTA1). Phenylmagnesium bromide was synthesized from
bromobenzene (3.14 g, 20.0 mmol) and magnesium turning
(0.50 g, 21.0 mmol) in dry THF. The solution was heated to
40 °C and carbon disulfide (1.53 g, 20.0 mmol) was added
dropwise over approximately 15 min, to produce a dark brown
solution. Methyl R-bromophenylacetate (5.00 g, 21.8 mmol) was
then added into the solution. The reaction temperature was
raised to 80 °C and maintained for 24 h. Ice water was then
added to the solution, before extracting the organic products
with diethyl ether three times. The combined organic extracts
were rinsed with water and dried over anhydrous magnesium
sulfate. After solvent removal, column chromatography was
undertaken (diethyl ether:n-hexane (1:9)) to afford an orange-
red oil (52.4%).
Exp er im en ta l Section
Gen er a l Da ta . Ma ter ia ls. All solvents, monomers, and
other reagents were purchased from Aldrich at the highest
purity available and used as received unless otherwise stated.
Methyl acrylate (MA, 99%), Styrene (99+%), methyl meth-
acrylate (MMA, 99%), and dimethyl acrylamide (DMA, 99%)
1H NMR, δ (ppm from TMS): 3.70 (3H, s, O-CH3, 5.65 (1H,
s, -S(Ph)CH-CO2Me), 7.20-7.48 (8H, m, Ar-H), 7.91 (2H,
dd, J ) 7.26, 1.31 Hz, -SC(Ar-H)S-).
were filtered before utilization through
a basic alumina
(Brockmann I) column, to remove the radical inhibitor. Tet-
rahydrofuran (THF, Riedel-deHae¨n, HPLC grade), triethyl-
amine (Lancaster, 99%) and N,N-dimethylformamide (99.9+%,
HPLC grade) (DMF) were dried over molecular sieves 4 Å. 2,2-
Azobis(isobutyronitrile) (AIBN, 99%) was recrystallized twice
from ethanol. Bromobenzene (99.9%), carbon disulfide (99.9+%,
HPLC grade), methyl-R-bromophenylacetate (97%), sodium
methanethiolate (25 wt % in methanol), 2-chloro-2-phenyl-
acetyl chloride (CPAC, 90%), L-lactic acid (85+% in water),
phenylmagnesium chloride (2 M solution in THF), and poly-
13C NMR, δ (ppm from TMS): 53.04 (CH) 58.70 (O-CH3)
126.92, 127.40, 128.81, 128.92, 129.30, 132.81, 133.21, 143.84
(CH of Ar), 166.95 (CdO), 226.72 (CS2).
FTIR (cm-1): 1736 (CdO); 1605-1444 (aromatic skeleton
area); 1225 (CdS); 1151 (C-O stretching); 577 (C-S stretch-
ing).
MS (EI): m/z ) 302 (M+), 269, 193, 149, 121, 77.
Anal. Calcd: C, 63.55;H, 4.67; S, 21.21. Found: C, 63.61;
H, 4.76; S, 21.29.
(ethylene glycol) methyl ester (MeOPEG) (Mn ) 5000 g mol-1
)
Syn th esis of S-Meth oxyca r bon ylp h en ylm eth yl Meth -
yltr ith ioca r bon a te (MCP MT, See Sch em e 3, CTA2). Car-
bon disulfide (5.51 g, 72.5 mmol) in diethyl ether was added
dropwise to a suspension of sodium methanethiolate (4.20 mL,
65.9 mmol) in diethyl ether (200 mL) at ambient temperature
over 30 min. After 2 h, the solvent was removed and the
residue extracted three times with ethyl acetate to afford
sodium methyl trithiocarbonate (81.0%). The crude product
was used without purification.
were used as received. Diethyl ether, ethyl acetate and
n-hexane were purchased from Riedel-deHae¨n (AR grade) Air-
and moisture-sensitive compounds were manipulated using
standard Schlenk techniques under a nitrogen atmosphere.
Magnesium turning (AnalaR) was purchased from BDH. All
cotton fabrics (scoured and bleached, fluorescent brightener-
free) were supplied from Whaleys Bradford Ltds. (WBL) and
dried overnight in a vacuum oven at 45 °C before use.
Size Exclu sion Ch r om a togr a p h y. Molecular weight dis-
tributions were recorded using size exclusion chromatography
(SEC) at ambient temperature using a system equipped with
a Polymer Laboratories 5.0 µm-bead-size guard column (50 ×
7.5 mm) and two Polymer Laboratories PLgel 5 µm MIXED-C
columns (molecular weight range of 2 000 000-500) with a
differential refractive index detector (Shodex, RI-101). Unless
otherwise stated, tetrahydrofuran was used as an eluent at a
flow rate of 1 mL min-1, and toluene was used as a flow rate
marker. Both poly(styrene) in the range 7 500 000-580 and
poly(methyl methacrylate) in the range of 1 944 000-1020
were used for calibrations.
Methyl R-bromophenylacetate (2.04 g, 8.90 mmol) was added
to the freshly prepared trithiocarbonate salt (1.30 g, 8.90
mmol) in 20 mL of ethyl acetate at room temperature. The
solution was stirred for 4 h and quenched with saturated
sodium chloride (25 mL). The aqueous layer was extracted with
ethyl acetate (3 × 50 mL) and the combined organic layer
washed with 10% HCl (50 mL), dried over anhydrous magne-
sium sulfate and filtered. After solvent removal, the residue
was separated by column chromatography using 0.1% ethyl
acetate in toluene affording a yellow, oily product (70.6%).
1H NMR, δ (ppm from TMS): 2.66 (3H, s, S-CH3), 3.70 (3H,
s, O-CH3), 5.79 (1H, s, -S(Ph)CH-CO2Me), 7.20-7.44 (5H,
m, Ar-H).
1
1H NMR Sp ectr oscop y. Both H (400 MHz) and 13C NMR
(100 MHz) spectra were recorded on a Bruker 400 UltraShield
spectrometer at 25 °C and d-chloroform was used as a solvent,
unless otherwise stated.
13C NMR, δ (ppm from TMS): 20.40 (S-CH3), 53.04 (CH),
58.70 (O-CH3), 96.10, 128.80, 129.10, 129.20, 132.90, (CH of
Ar), 166.95 (CdO), 222.30 (CS2).

Macromolecules, Vol. 37, No. 8, 2004
Versatile Chain Transfer Agents 2711
FTIR (cm-1): 1732 (CdO); 1607-1452 (aromatic skeleton
area); 1208 (CdS); 1158 (C-O stretching); 562 (C-S stretch-
ing).
organic solution was dried over anhydrous magnesium sulfate
and the solvent was evaporated in vacuo to give the chloro-
phenylacetic acid PLLA ester (PLLA-CPA) (85.0%).
1H NMR, δ (ppm from TMS): 1.50 (d, CH3 of PLLA), 1.61
(d, CH3 of lactacte unit), 4.40 (q, CH of PLLA), 5.20 (q, CH of
lactate unit), 5.40 (1H, s, CHCl(Ar), 7.38 (5H, m, Ar-H).
13C NMR, δ (ppm from TMS): 15.66 (CH3), 17.04 (CH3),
66.27 (CH), 69.40 (CH), 72.26 (CH), 125.92, 126.88, 127.15,
128.64, 129.18, 132.63, (CH of Ar), 169.64 (CdO), 169.86
(CdO).
MS (EI): m/z ) 272 (M+), 240, 149, 121, 97, 77.
Anal. Calcd: C, 48.50; H, 4.44; S, 35.31. C, 48.62; H, 4.53;
S. 35.46.
F u n ction a liza tion on Cotton Su r fa ce. Deter m in a tion
of th e Degr ee of Su bstitu tion (DS). The degree of substitu-
tion on cotton substrate was calculated gravimetrically via the
equation below.24
Mn ) 7200; PDI ) 1.44 (SEC, MMA calibration).
Syn th esis of P LLA)MCP DB. Phenylmagnesium chloride
(2 mL, 4 mmol) was stirred in a three-necked round-bottom
flask contained THF (10 mL). Carbon disulfide (1.00 mL, 16.6
mmol) was then added dropwise to give a dark brown solution.
This solution was added to a solution of PLLA-CPA (8.00 g,
1.11 mmol) in THF (100 mL) ,and the reaction was refluxed
overnight. The orange-red product was also reprecipitated in
100 mL of cold diethyl ether (72.0%).
DS ) 3{(OH)substituted/(OH)initial
}
where (OH)substituted is the number of moles of the substituted
groups on the cotton fabric and (OH)initial is the number of
moles of hydroxyl groups on the cotton fabric (determined by
weighing the cotton substrate and considering the molecular
weight of a repeating unit, bearing three hydroxyl groups24).
Acylation of Cotton with 2-Ch lor o-2-ph en ylacetyl Ch lo-
r id e (CP AC). Cotton fabric (4.26 g) was suspended and stirred
in a THF solution with triethylamine (0.75 mL, 72.4 mmol)
at 60 °C. CPAC (5.00 g, 53.0 mmol) was added dropwise for
30 min. The reaction was left stirring for another 4 h, then
cooled to room temperature. The light yellow fabric was
washed with THF (3 × 20 mL) and rinsed thoroughly with
deionized water. The treated cotton was oven-dried under
vacuum to give the chlorophenylacetic acid cotton ester (cot-
ton-CPA).
1H NMR, δ (ppm from TMS): 1.50 (d, CH3 of PLLA), 1.61
(d, CH3 of lactate unit), 4.4 (q, CH of PLLA), 5.20 (q, CH of
lactate unit), 5.31 (1H, s, -S(Ph)CH-CO2Me), 7.22-7.45 (8H,
m, Ar-H), 7.89 (2H, d, -SC(Ar-H)S-).
13C NMR, δ (ppm from TMS): 15.66 (CH3), 17.04 (CH3),
66.27 (CH), 69.40 (CH), 72.26 (CH), 125.92, 126.88, 127.15,
128.64, 129.18, 132.63, 133.01, 143.47 (CH of Ar), 169.64
(CdO), 169.86 (CdO), 225.45 (CS2).
FTIR (KBr disk, cm-1): 1759 (CdO); 1637 (CdC);1467
(CH3); 1090 (C-O-C).
Degree of substitution (DS) ) 0.53 (18%).
Anal. Calcd: C, 62.06; H, 10.15; S, 0.94. Found: C, 62.21;
H, 10.21; S, 1.11.
P r epar ation of Cotton )MCP DB. Phenylmagnesium chlo-
ride (2.25 mL, 4.50 mmol) was transferred in a dried two-neck-
round-bottom flask. Carbon disulfide (0.27 mL, 4.50 mmol) was
added dropwise to the round-bottom flask over 15 min and
the solution temperature was then raised to 40 °C, forming a
dark brown solution. The solution was transferred to another
flask containing cotton-CPA (1.92 g). The reaction tempera-
ture was then increased to 80 °C and left for 24 h. The
resulting fabric, of a characteristic orange color, was washed
with THF (3 × 20 mL) and then rinsed thoroughly with
deionized water. The treated cotton (cotton-MCPDB) was
oven-dried under vacuum.
Mn ) 6600; PDI ) 1.50 (SEC, MMA calibration).
Syn th esis of Ch lor op h en yla cetic Acid [P oly(eth ylen e
glycol) m et h yl est er ] E st er (MeOP E G)CP A). Poly-
(ethylene glycol) methyl ester (MeOPEG) (9.04 g, 1.80 mmol),
triethylamine (0.50 mL, 3.60 mmol), and CPAC (0.416 g, 2.200
mmol) were mixed in a round-bottom flask using dry THF (150
mL) as a solvent, and the solution was refluxed for 2 days at
atmospheric pressure. The solvent was then removed, and
dichloromethane (150 mL) was added. The resulting solution
was washed with saturated sodium hydrogen carbonate, and
the yellow organic phase was dried over anhydrous magnesium
sulfate. The solvent was then removed in vacuo to give an ester
of chlorophenylacetic acid with poly(ethylene glycol) methyl
ester (MeOPEG-CPA). The product (93.0%) was reprecipitated
in cold diethyl ether.
DS ) 0.45 (15%).
Ma cr och a in tr a n sfer a gen ts (Ma cr oCTAs). Syn th esis
of P oly(L-la ctic a cid ) (P LLA).25 L-Lactic acid (30.00 g, 284.0
mmols) and p-toluenesulfonic acid (0.106 g, 0.600 mmols) were
mixed in a round-bottom flask connected to a reflux condenser
with vacuum system. The solution was first dehydrated at 150
°C at atmospheric pressure for 2 h, then brought to a reduced
pressure of 100 Torr for 1 h. Tin(II) chloride dihydrate (0.062
g, 0.280 mmols) was added and the temperature was slowly
increased to 180 °C. The pressure of the system was reduced
gradually to reach 10 Torr. An increase of viscosity of the
system was observed, confirming the polycondensation. The
product was left to cool, then dissolved in chloroform, and
subsequently reprecipitated into an excess of cold diethyl ether.
The resulting product (9.40 g, 46%) was filtered and dried
under vacuum.
1H NMR (CDCl3, 298 K, 400 MHz), δ (ppm from TMS): 3.36
(s, O-CH3), 3.60 (s, CH2-CH2-O), 5.33 (1H, s, CHCl), 7.36
(5H, m, Ar-H).
13C NMR δ (ppm from TMS); 70.91 (O-CH3), 72.30 (O-
CH2), 69.40 (CH), 127.30, 127.76, 128.80, 129.11, 129.42,
133.21 (CH of Ar), 169.14 (CdO).
Mn ) 7300; PDI ) 1.11 (SEC, MMA calibration).
Syn th esis of MeOP EG)MCP DB. MeOPEG-CPA (4.00
g, 0.78 mmol) was placed in a round-bottom flask with dry
THF (100 mL), equipped with a condenser. Phenylmagnesium
chloride (1.50 mL, 3.00 mmol) was prepared as above, and
carbon disulfide (1.00 mL, 16.6 mmol) was added dropwise for
approximately 10 min, to lead to a dark brown solution. This
solution was added to the MeOPEG-CPA solution and was
allowed to reflux overnight. The orange-red product was
reprecipitated in cold diethyl ether to give MeOPEG-MCPDB
(98.0%).
1H NMR, δ (ppm from TMS): 1.50 (d, CH3 of PLLA), 1.61
(d, CH3 of lactacte unit), 4.40 (q, CH of PLLA), 5.20 (q, CH of
lactate unit).
13C NMR, δ (ppm from TMS): 15.66 (CH3), 17.04 (CH3),
66.27 (CH), 69.40 (CH), 169.64 (CdO).
FTIR (KBr disk, cm-1): 1759 (CdO); 1466 (CH3); 1091 (C-
O-C).
1H NMR, δ (ppm from TMS): 3.33 (s, O-CH3), 3.63 (s, CH2-
CH2-O), 5.65 (1H, s, -S(Ph)CH-CO2Me), 7.20-7.50 (8H, m,
Ar-H), 7.93 (2H, d, Ar-H).
Mn ) 8300; PDI ) 1.41 (SEC, MMA calibration).
Syn th esis of Ch lor op h en yla cetic Acid P LLA Ester .
Poly(l-lactic acid) (PLLA) (9.40 g, 1.13 mmol) was placed in a
three-necked round-bottom flask under nitrogen atmosphere.
Dry THF (100 mL) and dry triethylamine (1.00 mL, 7.20 mmol)
were transferred to the round-bottom flask. CPAC (0.472 g,
2.500 mmol) was added to the PLLA solution dropwise. The
reaction was refluxed and left for 10 h before the solution was
taken up in dichloromethane (200 mL) and rinsed with
saturated sodium hydrogen carbonate (10 mL). The resultant
13C NMR, δ (ppm from TMS): 70.91 (O-CH3), 72.30 (O-
CH2), 72.26 (CH), 127.30, 127.76, 128.80, 129.11, 129.42,
133.21, 133.51, 144.22 (CH of Ar), 169.14 (CdO), 227.07 (CS2).
FTIR (KBr disk, cm-1): 2889 (CH2 stretching); 1739 (CdO);
1640 (CdC); 1113 (C-O-C).
Anal. Calcd: C, 55.05; H, 8.90; S, 1.21. Found: C, 55.19; H,
9.03; S, 1.23.
Mn ) 7460; PDI ) 1.12 (SEC, MMA calibration).

2712 Perrier et al.
Macromolecules, Vol. 37, No. 8, 2004
P olym er iza tion s. Hom op olym er iza tion in Bu lk . Sty-
rene (12.70 g, 121.8 mmol), MCPDB (0.074 g, 0.244 mmol),
and R,R′-azoisobutyronitrile (AIBN; 0.004 g, 0.024 mmol) were
prepared, and 1 mL of the solution was transferred in different
ampules. Nitrogen gas was then flowed through the solutions
for 5 min. The ampules were placed in a water bath preheated
to 60 °C. Each ampule was taken out at various times (see
Figure 2, 9) and placed into an ice bath to quench the reaction.
Sch em e 2. Gen er a l Str u ctu r es of th e Ch a in Tr a n sfer
Agen ts (CTAs) Rep or ted in Th is Stu d y
1
The percentage conversions were measured by H NMR and
molecular weights and PDI were analyzed by SEC (see Figures
2 and 4, 9).
P olym er iza tion Usin g P LLA)MCP DB a s Ma cr oCTA.
Methyl methacrylate (90.50 mmol), PLLA-MCPDB (1.441 g,
0.181 mmol), and R,R′-azobis(isobutyronitrile) (AIBN) (0.003
g, 0.020 mmol) were transferred to an ampule with toluene (6
mL). The ampule was deoxygenated by flushing out with
nitrogen for approximately 10 min. The ampule was placed in
a preheated oil bath at 60 °C. The reaction was stopped after
60 h by cooling of the reaction tube in an ice bath and then
terminated by air. Poly(L-lactic acid)-block-poly(methyl meth-
acrylate) were reprecipitated in cold diethyl ether. (Conversion
) 52.4%, Mn ) 31 000, and PDI ) 1.33.)
P olym er iza tion Usin g MeOP EG)MCP DB a s Ma cr o-
CTAs. Methyl methacrylate (9.061 g, 90.5 mmol), MeOPEG-
MCPDB (1.350 g, 0.180 mmol), and R,R′-azobis(isobutyro-
nitrile) (AIBN) (0.003 g, 0.020 mmol) were added into an
ampule. Toluene (6 mL) was added to the ampule. The ampule
was deoxygenated with nitrogen for approximately 10 min and
then placed in a preheated oil bath at 60 °C. The reaction was
stopped after 60 h by cooling the reaction tube in an ice bath
and exposed to air. Poly(ethylene glycol) methyl ester-block-
poly(methyl methacrylate) was precipitated in cold diethyl
ether. (Conversion ) 24.3%, Mn ) 17,150, and PDI ) 1.28.)
P olym er iza tion Usin g Cotton Ma cr oCTAs. Styrene
(9.350 g, 90.00 mmol), cotton-MCPDB (0.018 g, 0.090 mmol),
and R,R′-azobis(isobutyronitrile) (AIBN) (0.002 g, 0.010 mmol)
were added in ampules in ratios of 10000:10:1. The ampules
were deoxygenated with nitrogen for approximately 10 min
and then placed in a preheated oil bath at 60 °C. After reaction
(99% conversion), the grafted cotton substrate was washed
three times with toluene, and twice with THF (while stirring
overnight) to remove nongrafted polymeric chains, mainly due
to the free radical initiator (<10%). The cotton substrate was
then submitted to acid hydrolysis in THF, using 35% hydro-
chloric acid, to isolate the grafted polymeric chains. The
solvents were removed in vacuo and water was added to the
product to precipitate the polymeric chains and remove the
mono and disaccharide residues from cotton hydrolysis. After
thoroughly discussed in many publications,18,19,21,26,27
but the specific case of ester leaving group has raised
very little interest.18,21,26,27 The substituents variation
on the C in R of the carbonyl group leads to generated
radicals of various stability (see Scheme 2): When X )
Y ) CH3, the R group is stable enough to form a radical,
but not reactive enough to add on monomer. Therefore,
a reasonably good controlled polymerization can be
obtained with styrene and acrylate derivatives, but poor
control is observed with methacrylates because of the
bulkiness of the generated radical.21 If X ) CH3 and Y
) H, the control of the polymerization of styrene and
acrylates is still achievable, but again a poor efficiency
toward methacrylate derivatives is observed.18,26 Fi-
nally, in the case of X ) Y ) H, the generated radical is
not very stable, and a poor control over the polymeri-
zation of styrene and acrylates is obtained, while no
control at all is observed for the polymerization of
methacrylates.26 It was therefore interesting to test the
capacity in controlling radical polymerization of a leav-
ing group with X ) Ph and Y ) H. The presence of a
phenyl group is anticipated to increase the stability of
the generated radical, while the H reduces its bulkiness.
In a recent publication, the CSIRO group reported the
use of a similar R group to synthesize a multiarm CTA.28
In another comunication by Lebreton et al., the same
R-bromophenyl acetic acid group is used for the syn-
thesis of a fluorinated CTA. In the latter case, promising
results were obtained in the polymerization of styrene
(S), methyl methacrylate (MMA), ethyl acrylate (EA),
and 1,3-butadiene.27 These types of radicals have also
been very efficient to control the polymerization of
styrene, acrylate, and methacrylate derivatives by atom
transfer radical polymerization.29-31 To confirm data
already published by others, we undertook the copper
mediated living radical polymerization of MMA in
toluene (50% v/v) using a classic initiator for this system
(ethyl-2-bromoisobutyrate) and methyl R-bromophen-
ylacetate. The results of these polymerizations are
summarized on Figure 1, which shows the evolution of
Mn and PDI with monomer conversion. Both initiators
control the living polymerization of MMA, but methyl
R-bromophenylacetate leads to lower PDI and a Mn
closer to that predicted.
drying, the sample was submitted to SEC analysis (Mn
106 900, PDI ) 1.35).
)
Resu lts a n d Discu ssion
Ch oice a n d Syn th esis of th e CTAs. In most cases,
CTAs for RAFT or MADIX polymerizations are not yet
commercially available and their synthesis is an im-
portant step in the process of polymer design. Unfor-
tunately, most of the CTAs that have so far been
reported to efficiently control the living radical polym-
erization of a wide range of vinyl monomers require
multistep and often complex reactions. Typical examples
can be found in the synthesis of cumyl dithiobenzoate
or 2-(2-cyanopropyl) dithiobenzoate.8 On the other hand,
the preparation of CTA through the use of R-haloesters
is remarkable as it often requires only a one-step
reaction, under less stringent conditions, and is more
quantitative. Unfortunately, such CTAs usually lead to
a poor control of the living radical polymerization of
most monomers.8,26
To test the influence of the Z group on the polymer-
izations, CTAs with Z ) phenyl (CTA1, Scheme 3) and
Z ) methanethiol (CTA2, Scheme 3) were synthesized.
It was anticipated that CTA1 would lead to a more
efficient chain transfer agent, as the intermediate
radical would be more stabilized,16,17 while CTA2 would
benefit from a more straightforward synthesis.
The synthesis of S-methoxycarbonylphenylmethyl
dithiobenzoate (Scheme 3, CTA1; MCPDB) was achieved
by a Grignard reaction, through the addition of methyl-
R-bromophenylacetate to a solution of phenylmagne-
sium bromide and carbon disulfide in THF. S-Methoxy-
carbonylphenylmethyl methyltrithiocarbonate (Scheme
For a CTA to efficiently control polymerization, its R
group needs to form a radical that not only is stable
enough to be formed but also is reactive enough to add
onto the double bond of the monomer. This has been

Macromolecules, Vol. 37, No. 8, 2004
Versatile Chain Transfer Agents 2713
F igu r e 2. Pseudo-first-order rate plot for the bulk polymer-
ization of styrene (9), methyl acrylate (b), dimethyl acrylamide
(1), and methyl methacrylate (2) mediated by S-methoxycar-
bonylphenylmethyl dithiobenzoate (MCPDB) at 60 °C.
F igu r e 1. Molecular weight and PDI evolution with monomer
conversion for the polymerization of methyl methacrylate in
toluene (50% v/v) at 90 °C using a ratio monomer/initiator/
copper(I)/ligand ) 100/1/1/2 with initiator ) ethyl 2-bro-
moisobutyrate (9) and methyl R-bromophenylacetate (b).
polymerization rates are obtained (especially in the case
of MA and DMA), while keeping good control of the
molecular weight (PDIs are generally below 1.2 when
using MCPMT).
3, CTA2; MCPMT) was prepared following the addition
of methyl-R-bromophenylacetate to a solution of sodium
methyl trithiocarbonate, prepared from carbon disulfide
and methanethiolate, in ethyl acetate at room temper-
ature. An additional feature of this reaction is that using
sodium methoxide instead of sodium methanethiolate
would lead to the preparation of the equivalent MADIX
agent (Scheme 3).
P olym er iza tion s. Both CTAs were tested in the
polymerization of styrene, methyl acrylate, methyl
methacrylate and dimethyl acrylamide. A common
feature of all polymerizations is the faster kinetics of
reaction when using MCPMT by comparison to MCPDB.
Indeed, MCPMT generates an intermediate radical 2
(Scheme 1) less stable than that formed from MCPDB
(The phenyl Z group of MCPDB is a better stabilizing
group than the methanethiol of MCPMT). It leads to a
higher rate of fragmentation of 2; therefore faster
Styr en e P olym er iza tion . Styrene is the most stud-
ied monomer in RAFT and MADIX polymerizations.
MCPDB and MCPMT show a similar control over its
polymerization, up to high conversion. Styrene polym-
erization is the slowest of all monomers (9.5% conver-
sion in 8 (MCPDB) or 7 h (MCPMT); Figures 2 and 3).
In both case the molecular weight increases linearly
with conversion, as expected for a living system. In the
case of MCPDB mediated polymerization, the values at
higher conversion are lower than theoretical predictions
(Figure 4). A reviewer has suggested that this could be
due to a low transfer constant of the CTA to styrene.
However, in each case, the polydispersity values average
1.1 (Note: For a better clarity of Figure 3, the point
corresponding to 86.7% after 166 h, Mn ) 30 700, PDI
) 1.08, has not been plotted.)
Meth yl Acr yla te P olym er iza tion . The polymeri-
zation mediated by MCPDB shows a good control, and
Sch em e 3. Syn th etic Sch em es for S-Meth oxyca r bon ylp h en ylm eth yl Dith ioben zoa te (MCP DB) a n d
S-Meth oxyca r bon ylp h en ylm eth yl Meth yltr ith ioca r bon a te (MCP MT)

2714 Perrier et al.
Macromolecules, Vol. 37, No. 8, 2004
F igu r e 3. Pseudo-first-order rate plot for the bulk polymer-
ization of styrene (9), methyl acrylate (b), dimethyl acrylamide
(1), and methyl methacrylate (2) mediated by S-methoxycar-
bonylphenylmethyl methyltrithiocarbonate (MCPMT) at 60
and 50 °C (methyl acrylate).
F igu r e 5. Molecular weight and PDI evolution with monomer
conversion34 for the bulk polymerization of styrene (9), methyl
acrylate (b), dimethyl acrylamide (1) and methyl methacrylate
(2) mediated by S-methoxycarbonylphenylmethyl methyl-
trithiocarbonate (MCPMT) at 60 °C and 50 °C (methyl acry-
late). The lines show the theoretical evolution of Mn with
conversion34 for poly(styrene) (-), poly(methyl acrylate) (- -),
poly(methyl methacrylate) (‚‚‚), and poly(dimethyl acrylamide)
(-.-).
resultant auto-accelerated reaction causing the mono-
mer to boil and the septum to break at the very start of
the reaction. To improve the efficiency of MCPMT as
chain transfer agent, the temperature was then lowered
to 50 °C. In these conditions, the reaction was faster
than that mediated by MCPDB at 60 °C: 6 h led to a
conversion of 8.1% when using MCPDB and 61.8% when
using MCPMT. The molecular weight increased linearly
with the monomer conversion, following very closely the
theoretical predictions (Figure 5). As in the case of
styrene, the PDI decreases with conversion to reach
values around 1.1.
Dim eth yl Acr yla m id e P olym er iza tion . Both CTAs
show a good control over the polymerization of DMA.
As in the case of MA, using MCPMT leads to an increase
in the speed of polymerization (18% in 8 h when using
MCPDB and 88% in 7 h with MCPMT, Figures 2 and
3). While in the case of MCPDB, the molecular weight
stays very close to that expected during the polymeri-
zation, the polymerization mediated by MCPMT leads
to a molecular weight slightly higher than anticipated,
possibly due to the fact that not all the CTA is consumed
and/or radical coupling inherent to LRP processes. This
observation should however be moderated by the fact
that the experimental molecular weights reported are
calculated using PMMA standards. In both cases, the
polydispersities remain under 1.2 (Figures 4 and 5).
Meth yl Meth a cr yla te P olym er iza tion . MCPDB
gives also good results in the polymerization of MMA.
As explained above, the polymerization is relatively slow
(Figure 2), but the molecular weight evolution is close
to theory within a reasonable error, and the PDI
obtained remains under 1.3 (Figure 4). To the best of
our knowledge, this is the first time the control of MMA
polymerization via RAFT is achieved with a leaving
group (R) showing a secondary carbon radical.
F igu r e 4. Molecular weight and PDI evolution with monomer
conversion for the bulk polymerization of styrene (9), methyl
acrylate (b), dimethyl acrylamide (1), and methyl methacry-
late (2) mediated by S-methoxycarbonylphenylmethyl dithioben-
zoate (MCPDB) at 60 °C. The lines show the theoretical
evolution of Mn with conversion34 for poly(styrene) (-), poly-
(methyl acrylate) (- -), poly(methyl methacrylate) (‚‚‚), and poly-
(dimethyl acrylamide) (-.-).
leads to polymers with molecular weight close to that
expected and low PDI (Figures 4). Figure 2 shows that
MA polymerization is far slower than MMA polymeri-
zation. This order is somewhat surprising when com-
pared to traditional kinetic data for classic free radical
polymerization of the two monomers. The fact that
MMA polymerization is faster than MA polymerization
can be explained by the better stability of the generated
radical in the case of MMA (Pm•, Scheme 1), which will
favor its formation and therefore enhance the overall
rate of polymerization. If we modify the Z group from a
phenyl to a methanethiol (MCPMT), the intermediate
radical 2 is less stable and therefore more prompt to
fragmentation. This leads to faster generation of propa-
gating radicals and therefore increases the overall speed
of reaction. Indeed, the polymerization of methyl acry-
late mediated by MCPMT was initially attempted at 60
°C. A significant exothermal was observed with the
The MCPMT mediated polymerization of MMA shows,
however, no control. At 60 °C, the molecular weight
evolution is different from that predicted by theory, with

Macromolecules, Vol. 37, No. 8, 2004
Versatile Chain Transfer Agents 2715
F igu r e 6. Molecular weight distribution evolution during
polymerization of methyl methacrylate in bulk mediated
by S-methoxycarbonylphenylmethyl methyltrithiocarbonate
(MCPMT) at 60 °C.
very high values at low conversion. The difference in
kinetics for each CTA is less obvious than that observed
for other monomers: 77.8% are reached in 20 h in the
case of MCPDB while it takes 20 h and 40 min to reach
86.7% when using MCPMT. When looking at the evolu-
tion of the molecular weight distribution during the
reaction (Figure 6), one can distinctly observe a bimodal
curve at low conversion. When the reaction proceeds to
high conversion, the two molecular weight distributions
level up and the PDI decreases (Figure 5). Similar
observations have already been made by Barner-
Kowollik et al.16 in the case of MMA polymerization
mediated by RAFT agents with a Z group that lowers
the stability of the intermediate radical 2 (Scheme 1).
On a similar model, we expect the methanethiol Z group
of MCPMT to induce slower reaction of the initial CTA
with the growing polymer chains by comparison to what
is observed with MCPDB. Furthermore, the fact that
MCPMT has a lower chain transfer constant with MMA
than with S, MA, and DMA, leads to the presence of
two different chain transfer agents at the start of the
reaction: the initial CTA which has not yet reacted and
a macroCTA generated by the addition of a polymeric
chain on the initial chain transfer agent.16 Both CTAs
have very different chain transfer constants, therefore
two parallel mechanisms occur, which generate two
different types of molecular weight distributions. Even-
tually, when the initial CTA is fully consumed, the
polymerization is only mediated by the macroCTA.
Steric hindrance effects facilitate the rapid growth of
the smallest chains, allowing homogenization of the
molecular weight distribution, as illustrated by a mono-
modal molecular weight distribution at high conversion
(Figure 6). The final product shows a reasonably low
PDI with a molecular weight lower than that expected.
To achieve a better control over the polymerization, we
tried to slow the growth of the polymer chains by
decreasing the temperature to 25 °C. However, similar
observations to that at higher temperature were made.
In conclusion, MCPMT is not as good CTA as MCPDB
for the polymerization of MMA. Nevertheless, polymers
with PDI < 1.4 and molecular weight slightly under that
expected can be obtained.
F igu r e 7. Molecular weight distribution of (a) poly(ethylene
glycol) (__) and [poly(ethylene glycol)-b-poly(methyl methacry-
late)] (- -), (b) poly(L-lactic acid) (__) and [poly(L-lactic acid)-b-
poly(methyl methacrylate)] (- -), and (c) poly(methyl meth-
acrylate) (__) and [poly(methyl methacrylate)-b-poly(styrene)]
(- -).
cumyl dithiobenzoate and cyanoisopropyl dithioben-
zoate.8 MMA polymerization, however, is well controlled
when mediated by MCPDB but lead to broader molec-
ular weight distributions in the presence of MCPMT.
En d Ch a in F u n ction a lities a n d P olym er ic Ar -
ch itectu r es. One of the main characteristic of living
radical polymerization is the use of various types of
functional molecules, or macromolecules, to initiate
polymerization. This has been well documented for
transition metal mediated living radical polymerization
in the particular case of R-haloesters initiators. The
appropriate acid halide can easily be reacted with
various functional groups through a straightforward
esterification reaction to form the corresponding initia-
tor.6,7,32 We used a similar approach to produce func-
tional CTAs for RAFT and MADIX from inexpensive
reagents and through a straightforward synthesis. A
molecule bearing a hydroxyl group is reacted with
2-chloro-2-phenylacetyl chloride to form the correspond-
ing 1-alkoxycarbonyl-1-phenyl methyl. The product is
then further reacted following the procedure highlighted
for MCPDB and MCPMT to form the corresponding
dithiobenzoate or trithioester, respectively (see Scheme
2).
By this process, block copolymers with polymers
formed by other (nonradical) mechanisms can easily be
synthesized. We chose MMA as the model monomer.
According to the previous kinetic studies, the polymer-
ization of MMA is the most difficult to control with
MCPDB. Therefore, achieving well-controlled architec-
tures with MMA should prove that good control could
also be achieved with the other monomers investigated
in this study. An amphiphilic AB block copolymer with
reasonably low PDI was formed by transforming a poly-
(ethylene glycol) methyl ether (MeOPEG) chain into
CTA, following the process described above, and its use
to polymerize MMA (see Table 1, entry 1). On the same
In conclusion, MCPDB and MCPMT offer good control
over the living polymerization of styrene, MA, and DMA
by comparison to more classic RAFT agents such as

2716 Perrier et al.
Macromolecules, Vol. 37, No. 8, 2004
Sch em e 4. Sch em e Sh ow in g th e Tr a n sfor m a tion of
Molecu les Bea r in g a Hyd r oxyl Gr ou p in to In itia tor
for Tr a n sition Meta l Med ia ted Livin g Ra d ica l
P olym er iza tion a n d /or Ch a in Tr a n sfer Agen t for
Rever sible Ad d ition F r a gm en ta tion Ch a in Tr a n sfer
(RAF T) a n d Ma cr om olecu la r Ar ch itectu r e Design via
In ter ch a n ge of Xa n th a te (MADIX) P olym er iza tion
F igu r e 9. Subtraction of FTIR spectra showing cotton ester
- cotton.
To demonstrate the versatility of the process, solid
suported polymerization was also undertaken. A recent
communication by Carlmark et al. has shown the
possibility to grow polymeric chains in a controll manner
from cotton substrate via transition metal mediated
living radical polymerization.34 However, the authors
had difficulty in characterizing the molecular weight of
the grafted chains. We decided to follow a similar route
using the principle highlighted above. The hydroxyl
groups of a cotton fabric were treated with 2-chloro-2-
phenylacetyl chloride and further transformed into
dithioesters to be used as supported CTA for polymer-
ization. Each reaction step was followed by Raman and
FTIR spectroscopy (Figures 8 and 9). Raman spectros-
copy (Figure 8, bottom spectrum) illustrates the suc-
cessful reaction of 2-chloro-2-phenylacetyl chloride with
the cotton hydroxyl groups by incorporation of the
Ta ble 1. Molecu la r Weigh t Da ta for AB Diblock
Cop olym er s
monomer
A
monomer
B
PDIb
Mn
PDIcopolymer
a
b,c
b
Mn
1 ethylene oxide 5000 1.12 MMA
17 150
31 000
63 600
1.28
1.33
1.27
1.35
1.38
2.22
2
L-lactic acid
3 MMA
4 cellulose
5 cellulose
6 cellulose
1800 1.50 MMA
13 400b 1.18 styrene
styrene 106 900d
MA
MMA
84 850
60 500
a
b
Determined by 1H NMR using CDCl3 as solvent. Determined
monosubstituted phenyl (1602, 1583, and 1004 cm-1
)
by SEC using THF as eluent and PMMA standards. c Mn of the
and the C-Cl bond (peak at 617 cm-1) of the acid
chloride. Further confirmation was also obtained from
FTIR spectroscopy, Figure 9, with stretches at 1736 and
1187 cm-1, characteristic of CdO and C-O, respectively.
d
copolymer. PS as SEC standards.
The transformation into dithioester is also illustrated
by Figure 9, where the strong Raman bands at 1236
and 651 cm-1 (top spectrum) are attributed to the CdS
and C-S bonds, respectively. The characteristic peaks
of aromatic structure are still observed at 1602 and 1001
cm-1, demonstrating the incorporation of an extra
phenyl ring. The degree of substitution of the hydroxyl
groups of the cotton fabric was estimated to be 14% by
gravimetry. The reactions were therefore prepared
aiming for a degree of polymerization DP ) [M]/[CTA],
with [CTA] obtained from the degree of substitution.
The cotton supported polymerizations of MMA, MA,
and styrene were undertaken in bulk, up to full conver-
sion. After polymerization, a sample of cotton was
hydrolyzed in acidic conditions to collect the grafted
PMMA, PS, and PMA chains, which were then analyzed
by SEC. Table 1 illustrates the remarkable control
obtained during polymerization of styrene and methyl
acrylate. PS and PMA (entries 3 and 4) show a molec-
F igu r e 8. Subtraction of Raman spectra showing cotton ester
- cotton (bottom) and cotton chain transfer agent - cotton
ester (top).
model, an AB block copolymer incorporating a bio-
degradable block, poly(L-lactic acid) (PLLA), and a
PMMA block was also produced (see Table 1, entry 2).
The GPC traces (Figure 8) show the clean conversion
of the initial polymer into a AB block copolymer after
addition of MMA. These results can be compared to
entry 3 (Table 1), which shows the molecular weight and
PDI of a PMMA-b-PS block copolymer synthesized by
further reacting a PMMA macroCTA (synthesized with
MCPDB) with styrene.
ular weight very close to that expected (Mn,theor
)
104 200 and 99 100, respectively) with polydispersities
as low as 1.35. In the case of PMMA (entry 6), a lower
molecular weight than anticipated was obtained
(Mn,theor ) 100 100), with higher PDI. Nevertheless, an
easy process for supported polymerization was demon-
strated, which leads to a remarkable control of the
polymeric chains molecular weight. Furthermore, this

Macromolecules, Vol. 37, No. 8, 2004
Versatile Chain Transfer Agents 2717
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Con clu sion
In conclusion, we have described the facile synthesis
of versatile CTAs that can produce an extensive range
of polymers with predictable Mn and low PDI from
styrene, methyl acrylate, methyl methacrylate, and
dimethyl acrylamide. Furthermore, these CTAs allow
the easy incorporation of any molecules bearing a
hydroxyl group at the end of a polymeric chain. We
believe this technique will provide new opportunities
in the synthesis of functional polymers, so far dominated
by atom transfer radical polymerization. Indeed, not
only will the use of RAFT/MADIX avoid the potential
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process is easier to undertake, with a wider range of
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Ack n ow led gm en t. P.T. acknowledges the financial
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Dr. Babiker Badri for their help on NMR and GC-MS,
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the data for all the polymerization reactions reported in this
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(34) Calculated using the following formula: Mn,theor ) [monomer]/
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and c the fractional conversion.
MA035468B