Heterocomplementary H-bonding RAFT agents as tools for the preparation of supramolecular miktoarm star copolymers

Article abstract of DOI:10.1021/ma101044y

Supramolecular miktoarm stars (AB₂ type) composed of poly (methyl methacrylate)-polystyrene₂ (PMMA-PS₂), poly(isoprene)-polystyrene₂ (PI-PS₂), and poly(vinyl acetate)-polystyrene₂ (PVAc-PS<

Full text of DOI:10.1021/ma101044y

Macromolecules 2010, 43, 5981–5988 5981
DOI: 10.1021/ma101044y
Heterocomplementary H-Bonding RAFT Agents as Tools for the
Preparation of Supramolecular Miktoarm Star Copolymers
‡
†
‡
‡
Senbin Chen,†,‡ Arthur Bertrand, Xijun Chang, Pierre Alcouffe, Catherine Ladaviere,
ꢀ
‡
Jean-Franc-ois Gerard, Frederic Lortie,* and Julien Bernard*
,‡
,‡
ꢁ
ꢁ ꢁ
†Department of Chemistry, Lanzhou University, Lanzhou 730000, Popular Republic of China, and
‡
ꢁ
Universite de Lyon, Lyon, F-69003, France, INSA de Lyon, IMP, Villeurbanne, F-69621, France,
and CNRS, UMR 5223, Ingeꢁnierie des Mateꢁriaux Polymeꢀres, Villeurbanne, F-69621, France
Received May 11, 2010; Revised Manuscript Received June 17, 2010
ABSTRACT: Supramolecular miktoarm stars (AB2 type) composed of poly (methyl methacrylate)-polystyrene2
(PMMA-PS2), poly(isoprene)-polystyrene2 (PI-PS2), and poly(vinyl acetate)-polystyrene2 (PVAc-PS2) were suc-
cessfully synthesized by assembling reversible addition-fragmentation chain transfer (RAFT)-polymerized chains
bearing hydrogen-bonding heterocomplementary associating units. To this end, thymine and diaminopyridine-
functionalized chain transfer agents were designed to efficiently mediate the polymerization of vinyl acetate, methyl
methacrylate, isoprene, and styrene. The selective associations of the resulting hydrogen-bonding macromolecular
building blocks PVAc/PS, PI/PS, and PMMA/PS were demonstrated by 1H NMR in CDCl3 solutions. Miktoarm
stars formation in the bulk was also confirmed by transmission electronic microscopy.
Introduction
units provided monofunctional and telechelic polymer chains,10
macromolecules containing embedded binding sites,3 and supra-
Despite the increasing attention paid to the construction of
supramolecular edifices,1 the development of well-defined supra-
molecular block copolymers or supramolecular stars from self-
assembly of tailor-made (end-functional) hydrogen-bonding macro-
molecules remains in its infancy in comparison with covalent
analogues.
Synthetic strategies affording the incorporation of hydrogen-
bonding units at a specific region of a polymer backbone (chain
ends, center of the chain) are indeed rather limited so far. Intro-
duction of associating motifs can be achieved through postpoly-
merization functionalization as described by Meijer and Binder,
together with others.2 However, this approach potentially suffers
from incomplete transformation of the macromolecules.
An elegant strategy to circumvent such synthetic issues consists
in incorporating molecular recognition units during the polymeriza-
tion process through the use of functionalized initiators, chain transfer
agents or chain terminators. Hydroxyl-functionalized hydrogen-
bonding modules based on 2,6-diamidopyridine (DAP),3 2-ureido-
4[1H]-pyrimidone (Upy),4 or bis-ureidodeazapterin (BisDeAP)5
have, hence, been successfully used as initiators for the ring-opening
molecular stars,5,11 as well as supramolecular block copolymers.12
Surprisingly, the preparation of supramolecular structures by
a combination of the most versatile CRP technique, that is, rever-
sible addition-fragmentation chain transfer polymerization/
macromolecular design via interchange of xanthate process
(RAFT/MADIX) and hydrogen bonding, has been scarcely
explored so far.
We recently reported the first example of supramolecular
hydrogen-bonding polymeric structures (poly(vinyl acetate)
3-arm stars) generated from chain transfer agents (CTA) bearing
complementary associating units.13
Extrapolating from our previous work, the present paper aims
at demonstrating that this strategy can afford a large range of
polymeric structures paving the way to the design of not only
synthetically challenging macromolecular architectures, but also
temperature and shear responsive materials. We propose in this
contribution an original approach to the versatile preparation of
AB2 type supramolecular miktoarm stars, a new class of hydro-
gen bonding polymeric structures, from the straightforward self-
assembly of RAFT-made macromolecular blocks bearing com-
plementary hydrogen-bonding motifs located either at one chain
end (thymine) or in the middle of the chain (DAP; see Scheme 1).
As a proof of concept, we describe herein the generation of typi-
cally synthetically challenging poly(isoprene)-polystyrene2 (PI-PS2),
poly(methyl methacrylate)-polystyrene2 (PMMA-PS2), and poly-
(vinyl acetate)-polystyrene2 (PVAc-PS2)14 supramolecular mikto-
arm stars from DAP- and thymine-functionalized heterocomple-
mentary H-bonding RAFT agents.
polymerization of D,L-lactide and ε-caprolactone. A series of
functionalized ruthenium ring-opening metathesis polymeriza-
tion initiators,6 chain terminators,6 and chain transfer agents7
have been recently developed to afford a panel of mono and
bifunctional (homo and heterotelechelic) polymer chains. The
ease and the versatility of radical polymerizations have also
encouraged researchers to generate well-defined polymers bear-
ing associating motifs through controlled radical polymerization
(CRP).8 Using uracil-functionalized alkoxyamine initiators,
Mather et al. reported the synthesis of (chain-end-functionalized)
H-bonding polystyrenes and poly(alkyl acrylate)s via nitroxide-
mediated polymerization (NMP).9 Atom transfer radical poly-
merization (ATRP) from H-bonding initiator (based on guanosine,
DAP, UPy, 2,7-diamido-1,8-naphthyridine, or BisDeAP) associating
Experimental Section
Materials. All the chemicals were purchased from Aldrich or
Fluka. Vinyl acetate (VAc) was freshly distilled prior to polymer-
ization. The other monomers were filtered prior to passing through
a column of basic aluminum oxide to remove inhibitors. Unless
otherwise indicated, the other chemicals were used without further
purification. CTA1 was synthesized as previously described.13
*To whom correspondence should be addressed. E-mail: julien.bernard@
insa-lyon.fr (J.B.); frederic.lortie@insa-lyon.fr (F.L.).
r 2010 American Chemical Society
Published on Web 07/02/2010
pubs.acs.org/Macromolecules

5982 Macromolecules, Vol. 43, No. 14, 2010
Scheme 1. General Strategy To Prepare AB2 Supramolecular Miktoarm Stars
Chen et al.
Characterization Methods. 1H and 13C NMR spectra were
recorded on a Bruker AVANCE250 (250 MHz) or AVANCE400
(400 MHz) spectrometer using CDCl3 or CD2Cl2. ESI-MS spectra
(m/z) were measured on a Thermo-Finnigan Mat 95XL. Thymine-
functionalized PVAc, PMMA, and PI and 2,6-diacyldiamino-
pyridine-functionalized PS were analyzed with an apparatus run-
dissolved in anhydrous THF and warmed for 24 h at 80 °C. 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 MgSO4.
After solvent removal, column chromatography was undertaken
(ethyl acetate/cyclohexane, 1/1, v/v) to afford CTA2 as a red solid
in moderate yield (0.91 g, 52%). ESI-MS Calcd for (C31H38N2-
O4S2þNa)þ, 589.8; found, 589.3 m/z. 1H NMR (CDCl3; [CTA2]=
ning in THF at 25 °C (flow rate: 1 mL min-1) and equipped with a
3
Viscotek VE 1121 automatic injector, three Waters HR5E columns,
and a differential refractive index detector (Viscotek VE3580). The
average molar masses of PVAc, PS, PI, and PMMA were derived
from a calibration curve based on PS and PMMA standards res-
pectively. In the case of PVAc samples, the obtained molar masses
were subsequently corrected using the Mark-Houwink-Sakurada
(MHS) relationship between PS and PVAc with MHS parameters
at 25 °C: KPS = 14.1 ꢀ 10-5 dL g-1, RPS = 0.70; KPVAc =16 ꢀ
10-5 dL g-1, and RPVAc =0.70. All MALDI-TOF mass spectra
were obtained with a Voyager-DE PRO (Applied Biosystems,
Framingham, MA) equipped with a nitrogen laser emitting at
337 nm with a 3 ns pulse duration. The instrument was operated in
reflector mode. The ions were accelerated under a potential of
20 kV. The positive ions were detected in all cases. The spectra were
the sum of 300 shots and an external mass calibration of mass
analyzer was used (a mixture of peptides, Sequazyme, Applied
Biosystems, Framingham, MA). Samples were prepared by mixing
45 or 20 μL of 1,8,9-anthracenetriol (dithranol, purchased by
1.68 ꢀ 10-2 mol L-1;δ(ppm)):1.26-1.65 (undecane CH2 groups,
3
18H), 1.91 (3H, s), 3.66 (2H, t), 4.13 (2H, t), 5.74 (1H, s) 6.97 (1H,
s), 7.30-7.41 (6H, m), 7.46-7.48 (2H, d), 7.77-7.83 (2H, d), 8.20
(1H, s). 13C NMR (CDCl3; δ (ppm)): 12.29, 25.72, 26.41, 26.93,
28.42, 29.16, 29.36, 29.64, 30.87, 40.78, 48.49, 58.97, 66.27, 110.38,
125.70, 125.79, 125.86, 125.90, 126.01, 128.41, 128.80, 129.01,
132.81, 133.46, 135.89, 140.51, 143.89, 151.23, 164.91, 168.83,
225.82.
Synthesis of CTA3. 2-Dodecylsulfanylthiocarbonylsulfanyl-
2-methyl-propionic acid (1.0 g, 2.7 mmol, 1.0 equiv) was dis-
solved in dry freshly distilled dichloromethane (50 mL) in a
round-bottom flask. The solution was cooled to 0 °C. Oxalyl
chloride (1.03 g, 8.1 mmol, 3 equiv) was added slowly under a
nitrogen atmosphere. The solution was allowed to reach room
temperature and stirred for a total of 3 h. The resulting solution
was concentrated under reduced pressure to yield the acid
chloride 3 (1.0 g, 99% yield). Compound 1 (0.7 g, 2.36 mmol)
was then dissolved in dry dichloromethane (40 mL) in a 100 mL
round-bottom flask and the solution was cooled to 0 °C. A solu-
tion of triethylamine (0.73 mL) in dichloromethane (5 mL) was
added dropwise over 10 min. A solution of 3 (1.0 g, 2.6 mmol) in
dichloromethane (5 mL) was added dropwise, and the solution
was allowed to reach room temperature while stirring for 3 h.
The solution was diluted with dichloromethane (100 mL) and
washed with saturated aqueous sodium bicarbonate solution
(50 mL), brine (50 mL), and water (50 mL), successively. The
organic layer was separated, dried over MgSO4, and filtered.
The supernatant was concentrated under reduced pressure. The
thymine-functionalized trithiocarbonate CTA3 was purified by
chromatography on silica gel (the separation was started with
methylene chloride/ethyl acetate 98/2, v/v and progressively
ethyl acetate was incorporated to reach 7/3, v/v). A yellow paste
was obtained (0.44 g, 29% yield). ESI-MS Calcd for (C33H58-
N2O3S3 þ K)þ, 666.1; found, 665.2 m/z. 1H NMR (CDCl3;
Sigma-Aldrich) at 10 g L-1 in THF, with 5 or 20 μL of PVAc or
3
PS solution (at 10 g L-1 in THF), respectively. To enhance
3
cationization of polymers, 5 μL of AgTFA or NaI (both from
Sigma-Aldrich, at 10 g L-1 in THF or acetone, respectively) were
3
added to solutions. Finally, resulting mixtures (0.5 μL) were
spotted on the MALDI sample plate and air-dried. TEM analyses
were performed on a Philips CM120 Transmission electron micro-
scope with an accelerating voltage of 80 kV, at the Centre Techno-
logique des Microstructures of the University of Lyon. The samples
were prepared from diluted polymer solutions (0.5 g L-1 in THF)
3
deposited onto carbon-coated Formvar copper grids. The solvent
was evaporated at room temperature. The grids were subsequently
exposed to RuO4 vapors (2 wt % of Ruthenium III chloride in
50/50 water/sodium hypochlorite solution) for 20 min (to stain the
PS domains).
Synthesis of CTA2. CTA2 was synthesized in three steps from
thymine. 1-(ω-Hydroxyundecyl)thymine (1, 1.05 g, 89%) was
first prepared as previously reported from 11-bromo-1-undecanol
(1.0 g, 3.98 mmol) and thymine (10.0 g, 79.3 mmol).13 To a
solution of 1 (1 g, 3.36 mmol) and pyridine (1.7 g, 21.5 mmol) in
anhydrous THF (150 mL), an excess of 2-chloro-2-phenylacetyl
chloride (2.0 g, 10.5 mmol) was added dropwise. The solution
was stirred for one day at 60 °C. After solvent removal, the
resulting brown oil was dissolved in ethyl acetate and succes-
sively washed with brine, saturated sodium bicarbonate, and a
0.1 M HCl solution. The organic layer was subsequently dried
over MgSO4, and the product was purified by silica gel (Kiesigel-
60) column chromatography (ethyl acetate/cyclohexane, 1/1, v/
v) to give the benzyl halide 2 as a yellow solid (1.20 g, 80%).
Compound 2 (1.2 g, 2.7 mmol) and freshly synthesized phenyl-
dithiocarboxylic acid magnesium bromide (60 mmol) were
[CTA3] = 1.68 ꢀ 10-2 mol L-1; δ (ppm)): 0.86 (t, 3H, CH3-
3
C9H18-CH2-CH2-S-CdS), 1.23-1.80 (m, 36H, CH3-C9H18-
CH2-CH2S-CdS and N-CH2-C9H18-CH2-O), 1.71 (s, 6H, -S-
C(CH3)2-CO, 1.90 (s, 3H, CH3-CdCH), 3.22 (t, 2H, CH3-
C9H18-CH2-CH2-S-CdS), 3.64 (t, 2H, N-CH2-C9H18-CH2-O),
4.04 (t, 2H, N-CH2-C9H18-CH2-O), 6.97 (s, 1H, CH3-CdCH-),
8.28 (s, 1H, NH). 13C NMR (CDCl3) δ (ppm): 12.63, 14.42,
22.97, 25.68, 26.18, 26.74, 27.20, 28.18, 28.64, 29.23, 29.40, 29.45,
29.49, 29.63, 29.71, 29.74, 29.85, 29.92, 32.20 37.15, 48.88, 56.32,
66.41, 110.81, 140.77, 151.21, 164.72, 173.32, 221.66.
Synthesis of CTA4. N,N0-2,6-Pyridinediylbis(2-bromopropan-
amide) 4 was prepared as previously reported.3 Freshly synthe-
sized dithiobenzoic acid (20.3 g, 130 mmol) and 4 (5 g, 13 mmol)
were dissolved in THF (300 mL) and stirred at 60 °C for 15 h.

Article
Macromolecules, Vol. 43, No. 14, 2010 5983
The reaction solution was then cooled to room temperature,
washed with brine and water. The organic layer was collected
and dried over MgSO4. The product was purified by column
chromatography (dichloromethane/cyclohexane, 2/1, v/v) to
give CTA4 as a red solid (3.1 g, 45%).ESI-MS Calcd for
(C25H23N3O2S4 þ Na)þ, 548.7; found, 548.0 m/z. 1H NMR
Scheme 2. Structure of Thymine and DAP-Functionalized H-Bonding
CTAs
(CDCl3; [CTA4]=3.36 ꢀ 10-2 mol L-1; δ (ppm)): 1.73 (6H,
3
t), 4.85 (2H, q), 7.37 (4H, t), 7.55 (2H, t), 7.86 (2H, d), 7.98 (4H,
t), 8.56 (NH, 2H). 13C NMR (CDCl3) δ (ppm): 15.99, 49.04,
110.01, 127.21, 127.22, 127.42, 127.45, 133.18, 140.75, 143.98,
149.22, 168.80, 226.81.
Polymerizations. Polymerization of VAc. Bulk polymeriza-
tion of VAc was performed using 2,20-azobisisobutyronitrile
(AIBN) as initiator and CTA1 as chain transfer agent. Typically,
the polymerization of VAc (3 mL, 3.25 ꢀ 10-2 mol) was carried
out using AIBN (2.2 mg, 1.34 ꢀ 10-5 mol), CTA1 (62.4 mg, 1.32 ꢀ
10-4 mol), and trioxane (243 mg, 2.7 ꢀ 10-3 mol) as an internal
reference for the measurement of VAc consumption via 1H NMR.
A stock solution was transferred into Schlenk tubes that were
thoroughly deoxygenated by five consecutive freeze-pump-
thaw cycles. The tubes were subsequently placed in an oil bath
thermostatted at 60 °C. The reaction was stopped by plunging
the tubes into liquid nitrogen. The polymer was subsequently
precipitated twice into pentane to eliminate residual monomer
and trioxane. The polymer was dried under vacuum and char-
acterized by 1H NMR and SEC. The molecular weights of the
pure PVAc were finally evaluated by 1H NMR (CDCl3) from the
relative integration of the protons of the PVAc backbone (CH2-
CH-, nH, δ=4.85 ppm, with n being the degree of poly-
merization) and of characteristic protons of the thymine end
group (CdCH-N, 1H, δ=6.97 ppm).
(1.2-addition) and -C(CH3)dCH2 (3,4-addition)) and of char-
acteristic protons of the thymine end group ((CdCH-N, 1H, δ=
6.97 ppm).
Polymerization of Styrene. Bulk polymerization of styrene
was performed using 2,20-azobisisobutyronitrile (AIBN) as in-
itiator and CTA4 as chain transfer agent. Typically, the poly-
merization of styrene (4 mL, 3.5 ꢀ 10-2 mol) was carried out
using AIBN (0.36 mg, 2.2 ꢀ 10-6 mol), CTA4 (22.8 mg, 4.4 ꢀ
10-5 mol), and trioxane (243 mg, 2.7 ꢀ 10-3 mol) as an internal
1
reference for the measurement of styrene consumption via H
NMR. A stock solution was transferred into Schlenk tubes which
were thoroughly deoxygenated by five consecutive freeze-
pump-thaw cycles. The tubes were subsequently placed in an oil
bath thermostatted at 80 °C. The reaction was stopped by
plunging the tubes into liquid nitrogen. The polymer was sub-
sequently precipitated twice into ethanol to eliminate residual
monomer and trioxane. The polymer was dried under vacuum
and characterized by SEC and 1H NMR.
Polymerization of Methyl Methacrylate. Solution polymeri-
zation of methyl methacrylate was performed using 2,20-azobi-
sisobutyronitrile (AIBN) as initiator and CTA2 as chain trans-
fer agent. Typically, the polymerization of MMA (3 mL, 2.8 ꢀ
10-2 mol) was carried out using AIBN (0.59 mg, 3.6 ꢀ 10-6 mol),
CTA2 (40 mg, 7.1 ꢀ 10-5 mol), toluene (6 mL, 5.7 ꢀ 10-2 mol),
and trioxane (243 mg, 2.7 ꢀ 10-3 mol) as an internal reference
Results and Discussion
Aiming at generating well-defined AB2 type supramolecular
miktoarm stars, four different CTAs (Z-CS2-R) bearing either
thymine or DAP heterocomplementary recognition units have
been prepared: a thymine-functionalized xanthate (CTA1), a
thymine-functionalized dithiobenzoate (CTA2), a thymine-func-
tionalized trithiocarbonate (CTA3), and a DAP-functionalized
dithiobenzoate (CTA4), respectively, expected to efficiently medi-
ate the radical polymerization of VAc, MMA, isoprene, and
styrene (see Scheme 2).
Because introducing the associating motifs through the Z
“activating group” can be accompanied by an important loss of
functionality due to hydrolysis, aminolysis, or termination reac-
tions, thymine and DAP units were purposely incorporated as
part of the “R” leaving/initiating group.
1
for the measurement of MMA consumption via H NMR. A
stock solution was transferred into Schlenk tubes which were
thoroughly deoxygenated by five consecutive freeze-pump-
thaw cycles. The tubes were subsequently placed in an oil bath
thermostatted at 60 °C. The reaction was stopped by plunging
the tubes into liquid nitrogen. The polymer was subsequently
precipitated twice into cyclohexane to eliminate residual mono-
mer and trioxane. The polymer was dried under vacuum and
characterized by 1H NMR and SEC. The molecular weights of
1
the pure PMMA were finally evaluated by H NMR (CDCl3)
from relative integration of the protons of the PMMA backbone
(-O-CH3, 3nH, δ = 3.58 ppm, with n being the degree of
polymerization) and of characteristic proton of the thymine
end group (CdCH-N, 1H, δ=6.97 ppm).
Using a well-established method based on 1H NMR monitor-
ing, supramolecular associations of CTA1, CTA2, and CTA3,
with CTA4 through selective three-points H-bonding complexa-
tion were evidenced in solution in deuterated chloroform by a
significant downfield shift of the NH thymine proton (from
8.22 to 10.45 ppm for CTA1/CTA4, 8.19 to 10.38 ppm for
CTA2/CTA4, and 8.28 to 10.36 ppm for CTA3/CTA4, see
Figure 1) observed after addition of 1 equiv of heterocomple-
mentary CTA4. Titration experiments and a relevant mathema-
tical model were used to measure binding constants, which were
found to be 120-140 M-1 for each couple of CTA (see Support-
ing Information).
Radical polymerizations were subsequently carried out in the
presence of the appropriate H-bonding CTA and a minimum
concentration of thermal initiator, that is, [CTA]/[initiator]=10
for vinyl acetate and 20 for styrene, methyl methacrylate, and
isoprene, to minimize the number of unfunctionalized (and, thus,
nonassociating) chains.
Polymerization of Isoprene. Bulk polymerization of isoprene
was performed using dicumyl peroxide (DCP) as initiator and
CTA3 as chain transfer agent. Typically, the polymerization of
isoprene (4 mL, 4.0 ꢀ 10-2 mol) was carried out using DCP (1.08
mg, 4.0 ꢀ 10-6 mol) and CTA3 (51.4 mg, 8.0 ꢀ 10-5 mol). A
stock solution was transferred into Schlenk tubes that were
thoroughly deoxygenated by five consecutive freeze-pump-
thaw cycles. The tubes were subsequently placed in an oil bath
thermostatted at 120 °C. The reaction was stopped by plunging
the tubes into liquid nitrogen. The polymer was subsequently
precipitated twice into methanol to eliminate residual mono-
mer. The polymer was dried under vacuum and characterized
by 1H NMR and SEC. The molecular weights of the pure
1
PI were finally evaluated by H NMR (CDCl3) from relative
integration of the protons of the PI backbone (5.6-5.9 ppm
for the -CHdCH2 from the 1.2-addition polymerization,
5.0-5.5 ppm for -CHdC(CH3)- for the 1,4-addition poly-
merization, and 4.4-5.0 ppm for the mixture of -CHdCH2

5984 Macromolecules, Vol. 43, No. 14, 2010
Chen et al.
Figure 1. NMR spectra of thymine/DAP-functionalized CTAs (a, CTA1; b, CTA2; c, CTA3; d, CTA4) and their stoichiometric mixtures (e, CTA1/
CTA4; f, CTA2/CTA4; g, CTA3/CTA4) at 20 °C in CDCl3 ([THY] = [DAP] = 1.68 ꢀ 10-2 mol L-1). Red sphere: thymine NH protons; green cross:
3
DAP NH protons.
Figure 2. (A) First-order kinetic plot of the bulk polymerization of vinyl acetate at 60 °C in the presence of CTA1: [M]/[CTA] = 250, [CTA]/[AIBN] =
10. (B) Evolution of the normalized SEC traces in THF for the CTA1-mediated bulk polymerization of vinyl acetate at 60 °C ([VAc]/[CTA1] = 250;
[CTA1]/[AIBN] = 10) at different conversions. From right to left, THY-PVAc2, THY-PVAc3, THY-PVAc4, and THY-PVAc5. (C) First-order
kinetic plot of the bulk polymerization of styrene at 80 °C in the presence of CTA4: [M]/[CTA] = 800, [CTA]/[AIBN] = 20. (D) Evolution of the
normalized SEC traces in THF for the CTA4-mediated bulk polymerization of styrene at 80 °C at different conversions: from right to left, PS-DAP-
PS1, PS-DAP-PS2, PS-DAP-PS3*, and PS-DAP-PS4*. *The tail observed at low molecular weight reflects the presence of unfunctionalized chains
generated from thermal decomposition of AIBN and thermal self-initiation of styrene.
All CTAs were proven to effect a good control of the poly-
merizations. As an example, conversion versus time plots for the
polymerization of VAc and styrene, respectively, mediated with
CTA1 and CTA4 are given in Figure 2A,C (details of MMA and

Article
Macromolecules, Vol. 43, No. 14, 2010 5985
Table 1. Properties of the RAFT-Made H-Bonding Homopolymers
sample
CTA
[M]/ [CTA]
conva %
Mn,thb (g/mol)
Mn,NMRc g/mol
Mn,SEC g/mol
PDI
THY-PVAc1
THY-PVAc2
THY-PVAc3
THY-PVAc4
THY-PVAc5
THY-PMMA1
THY-PMMA2
THY-PMMA3
THY-PMMA4
THY-PI1
THY-PI2
THY-PI3
THY-PI4
PS-DAP-PS1
PS-DAP-PS2
PS-DAP-PS3
PS-DAP-PS4
PS-DAP-PS5
1
1
1
1
1
2
2
2
2
3
3
3
3
4
4
4
4
4
250
250
250
250
250
400
400
400
400
500
500
500
500
800
800
800
800
70
4
1400
6500
9400
10200
13700
7400
10900
15300
18600
6300
10200
13500
17700
5500
1400
5000
10800
12600
17500
7900
12100
17500
21900
9800
11700
15000
15900
5100
1200d
1.40d
1.29d
1.28d
1.34d
1.44d
1.34e
1.37e
1.33e
1.35e
1.30 f
1.31 f
1.26 f
1.35 f
1.19 f
1.18 f
1.17 f
1.18 f
1.33 f
30
43
46
62
17
26
37
45
23
28
38
50
6
5900d
11500d
13800d
18700d
9300e
13600e
18900e
21000e
9700 f
12400 f
14600 f
16500 f
6200 f
11
18
22
15
9300
8700
10200 f
16400 f
19400 f
1600 f
14900
18700
1500
15800
17900
1800
a Conversion from 1H NMR. b Number-average molecular weight was evaluated from the following equation: Mn,th = conv ꢀ ([M]/[CTA]) ꢀ mM
þ
mCTA.
c Determined from 1H NMR (CDCl3) from relative integration of the thymine or aromatic chain end group peaks and polymer backbone peaks.
d From SEC in THF (PS calibration). Molecular weight corrected with the following Mark-Houwink-Sakurada parameters at 25 °C: KPS = 14.1 ꢀ
10-5 dL g-1, RPS = 0.70; KPVAc = 16 ꢀ 10-5 dL g-1, RPVAc = 0.70. e From SEC in THF (PMMA calibration). f From SEC in THF (PS calibration).
3
3
Figure 3. Positive MALDI-TOF mass spectrum of THY-PVAc1 (with NaI salt and dithranol matrix) in the reflector mode. The inset shows an
enlarged region of this mass spectrum and illustrates the agreement between experimental and calculated monoisotopic mass (example given for DP =
10, C62H96N2O25S2Na). The assignment of minor population at ca. þ22 m/z vs main population is unknown for the moment.
isoprene polymerization are given in Supporting Information).
Polymerizations proceeded with pseudo-first-order kinetics,
indicative of a constant number of propagating centers. As
expected for a controlled process, molar masses increased linearly
with conversion, and SEC traces exhibited monodisperse peaks.
Molar masses determined by SEC were close to theoretical values
(Table 1).
The 1H NMR analyses clearly demonstrated the incorporation
of the thymine functionality in R-position of the PMMA, PI and
PVAc backbones with the presence of characteristic peaks at 6.97
and 8.13 ppm (respectively -CdCH-N- and NH) and the molar
masses evaluated from relative integration of the protons of the
polymer backbones and of the protons of the associating chain
end were in very good agreement with theoretical values.
A further evidence of the growth of the polymers in a con-
trolled fashion was given by the polydispersity index, which typi-
cally is comprised of values between 1.17 and 1.44, with molar
masses ranging from 1.2 to 21ꢀ103 g/mol (Table 1).
Further evidence of the chain functionalization were given by
MALDI-TOF mass spectroscopy analyses. For instance, the
MALDI-TOF mass spectrum of THY-PVAc1 observed in the
reflector mode (Figure 3) highlighted the presence of dominant

5986 Macromolecules, Vol. 43, No. 14, 2010
Chen et al.
Figure 4. Positive MALDI-TOF mass spectrum of PS-DAP-PS5 (with AgTFA salt and dithranol matrix) in the reflector mode. The inset shows an
enlarged region of this mass spectrum and illustrates the agreement between experimental and calculated monoisotopic mass for DP = 9 (C99H99N3O2Ag,
experimental = 1468.8 m/z, theoretical = 1468.7 m/z). The assignment of minor population at -9 m/z vs main population is unknown for the moment.
species undoubtedly corresponding to PVAc chains bearing a
thymine R-extremity and a xanthate ω-extremity as confirmed by
the very satisfactory agreement between (i) the experimental and
calculated monoisotopic mass (illustration on the degree of poly-
merization, DP of 10 in the inset of Figure 3) and (ii) the experimental
and simulated isotopic peak pattern (see Supporting Information).
Concerning PS-DAP-PS5, MALDI-TOF mass spectrometry
technique also confirmed the functionalization of PS chains by
the DAP moiety (Figure 4). Unfortunately, the labile dithioester
end groups (particularly in the PS chains) were difficult to detect
by this technique. The dithioester elimination in the mass spectro-
meter, due to the weakness of the C-S bond between PS and
CTA, leads to a stable conjugated double bond.15,16 As a result,
the main population detected in the PS-DAP-PS5 mass spectrum
was (Ph)CHdCH-PSx1-DAP-PSx2-CHdCH(Ph). Nevertheless,
the control of molecular weights with conversion (Table 1) and
1H NMR analyses clearly corroborated the presence of dithio-
benzoate moieties in the polymer chains.
1H NMR in deuterated chloroform. As expected for the forma-
tion of the selective three-point hydrogen-bonded THY-DAP
complex, the addition of 1 equiv of PS-DAP-PS1 to THY-PI1,
THY-PMMA1, and THY-PVAc2 was accompanied by a sig-
nificant downfield shift of the NH thymine proton from 8.0/8.05/
8.08 to 8.74/8.72/8.75 ppm, respectively, that clearly demon-
strated the generation of PI-PS2, PMMA-PS2, and PVAc-PS2
supramolecular miktoarm stars (see Figure 5; the association
between THY-PI1 and PS-DAP-PS1 is given in Supporting
Information). The strength of the heterocomplementary hydro-
gen-bonding polymeric building association was subsequently
investigated by plotting the thymine NH chemical shift as a
function of PS-DAP-PS1 to THY-PVAc2, THY-PI1, or THY-
PMMA1 concentrations (see Supporting Information). The Kass
for the THY-DAP association between PS and PVAc, PI or
PMMA H-bonding chains were comparable (80-90 ( 5 M-1),
suggesting that the chemical nature of the polymer backbones
does not interfere with the H-bonding recognition process in
CDCl3 solutions. The association constants are quite lower than
Kass (120-140 M-1) of the H-bonding CTAs, indicating that the
presence of the polymeric chains slightly affects the association
ability of thymine and DAP moieties possibly due to the altered
accessibility of the DAP group at the center of the PS chain.
Finally, 1:1 bulk mixtures of THY-PVAc2/PS-DAP-PS1 and
PVAcunf/ PS-DAP-PS1 as reference (PVAcunf being an unfunc-
As previously shown by Binder, Weck, and others,2d,6,7a 1H
NMR monitoring constitutes one of the most suitable techniques
to study the H-bonding association of macromolecular blocks
and determine the association constant of the system. Conse-
quently, the formation of the miktoarm stars by self-assembly
through hydrogen bonding of PVAc (THY-PVAc2), PI (THY-
PI1), or PMMA ((THY-PMMA1)/PS (PS-DAP-PS1)) hetero-
complementary polymeric building blocks was investigated by
tionalized PVAc with molecular weight -Mn,SEC=5600 g mol-1
3

Article
Macromolecules, Vol. 43, No. 14, 2010 5987
Figure 5. NMR spectra of PS-DAP-PS1 (A), THY-PMMA1 (B), THY-PVAc2 (C), THY-PVAc2/PS-DAP-PS1 stoichiometric mixture (D), and
THY-PMMA1/PS-DAP-PS1 stoichiometric mixture (E) at 20 °C in CDCl3 ([THY] = [DAP] = 3 ꢀ 10-3 mol L-1).
3
Figure 6. TEM pictures of 1/1 blend of PVAcunf/PS-DAP-PS1 (A), 0.5/0.5/1 blend PVAcunf/THY-PVAc2/PS-DAP-PS1 (B), and 1/1 blend of
THY-PVAc2/PS-DAP-PS1 (C).
and PDI=1.36, in close agreement with THY-PVAc2) were
generated by simply mixing polymer chains in an appropriate
solvent for block solubilization followed by slow evaporation of
the solvent. The resulting morphologies were subsequently ob-
served by transmission electron microscopy (Figure 6), whereas
unfunctionalized PVAc and PS-DAP-PS1 polymer blends clearly
exhibited poorly dispersed domains, macrophase separation was
prevented for H-bonding PVAc and PS macromolecular blocks
blends, in agreement with the formation of supramolecular
miktoarm stars (Figure 6C).
middle of the chain. The self-assembly of these heterocomple-
mentary H-bonding polymer chains afforded the straightforward
generation of synthetically challenging supramolecular miktoarm
stars. We envisage that this new category of RAFT agents
would constitute a versatile platform for the design of a large array
of tailored supramolecular polymers. In addition, the reversible
nature of the association between the building blocks paves the way
to new properties as compared to the covalent counterparts.
Acknowledgment. The authors gratefully acknowledge the
French Ministry of Research, the CNRS (ANR Jeune Chercheur
SUPRABLOCK), and the Chinese Scholarship Council for their
financial support. Once again, the authors dedicate this work to
Professor Jean-Pierre Pascault for his whole-hearted support.
In summary, we have designed a series of original heterocom-
plementary H-bonding chain transfer agents allowing the gene-
ration of a panel of well-defined macromolecular building blocks
with associating motifs located either at one chain end or in the

5988 Macromolecules, Vol. 43, No. 14, 2010
Chen et al.
Supporting Information Available: Kinetic studies, determi-
nation of Kass, and comparisons between experimental and
simulated isotopic peak patterns of THY-PVAC1 obtained by
MALDI-TOF mass spectroscopy. This material is available free
of charge via the Internet at http://pubs.acs.org.
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