Synthesis of functionalized poly(vinyl acetate) mediated by alkyne-terminated RAFT agents

Article abstract of DOI:10.1039/c5ra15580k

Two new xanthates with alkyne functionalities were synthesized for the reversible addition fragmentation chain transfer (RAFT) polymerization of vinyl acetate (VAc). The new RAFT agents were fully characterized by ¹H and ¹³C NMR spectroscopy. Unlike the alkyne terminated RAFT agent (AT-X₁) the protected alkyne-terminated RAFT agent (PAT-X₁) was able to conduct the RAFT polymerization of VAc with a good control over the molecular weight (MW) and relatively narrow MW distributions (< 1.4). The linear evolution of M_n with conversion as well as the close agreement between M_n,th and M_n,GPC values confirmed the controlled features of the RAFT system. It is worth mentioning that the polymer dispersity remained very low (< 1.20) until relatively high monomer conversions (60%) due to the non-activated nature of VAc. The chain end-functionality of the obtained polymers was evaluated by ¹H NMR, FTIR-ATR and UV-Vis absorption analysis. The "livingness" of the obtained polymer was confirmed by a successful chain extension experiment. The deprotection of the alkyne functionality in the PVAc, allowed a further copper catalyzed azide-alkyne [3 + 2] dipolar cycloaddition reaction (CuAAC) with an azido terminated-poly(ethylene glycol) (PEG-N₃), to afford PVAc-PEG block-copolymers as a proof-of-concept.

Full text of DOI:10.1039/c5ra15580k

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Synthesis of functionalized poly(vinyl acetate)
mediated by alkyne-terminated RAFT agents†
Cite this: RSC Adv., 2015, 5, 91225
Joana. R. Gois,a Anatoliy V. Popov,b Tamaz Guliashvili,a Armenio C. Serraa
´
´
a
*
and Jorge F. J. Coelho
Two new xanthates with alkyne functionalities were synthesized for the reversible addition fragmentation
chain transfer (RAFT) polymerization of vinyl acetate (VAc). The new RAFT agents were fully
characterized by 1H and 13C NMR spectroscopy. Unlike the alkyne terminated RAFT agent (AT-X1) the
protected alkyne-terminated RAFT agent (PAT-X1) was able to conduct the RAFT polymerization of VAc
with a good control over the molecular weight (MW) and relatively narrow MW distributions (Đ < 1.4).
The linear evolution of Mn with conversion as well as the close agreement between Mn,th and Mn,GPC
values confirmed the controlled features of the RAFT system. It is worth mentioning that the polymer
dispersity remained very low (Đ < 1.20) until relatively high monomer conversions (60%) due to the
1
non-activated nature of VAc. The chain end-functionality of the obtained polymers was evaluated by H
NMR, FTIR-ATR and UV-Vis absorption analysis. The “livingness” of the obtained polymer was confirmed
by a successful chain extension experiment. The deprotection of the alkyne functionality in the PVAc,
allowed a further copper catalyzed azide–alkyne [3 + 2] dipolar cycloaddition reaction (CuAAC) with an
azido terminated-poly(ethylene glycol) (PEG-N3), to afford PVAc–PEG block-copolymers as a proof-of-
concept.
Received 4th August 2015
Accepted 15th October 2015
DOI: 10.1039/c5ra15580k
www.rsc.org/advances
The reversible deactivation radical polymerization (RDRP) has hydrolyzed derivative, poly(vinyl alcohol) (PVA), that extends its
witnessed enormous improvements during the last two applications to the biomedical eld.27
decades.1–5 For RDRP of activated monomers such as acrylates,
The choice of the RAFT agent, is of outmost importance for
methacrylates or styrene, different modications of atom the success of this RDRP method.28,29 For non-activated
transfer radical polymerization (ATRP) have successfully been monomers, xanthate mediated RAFT polymerization30 is one of
applied.6–10 However, the development of new RDRP systems the most straightforward RDRP strategies to afford optimal
that are able to polymerize such non-activated monomers, such control over the polymerization. Due to the high reactivity of
as vinyl chloride,11–13 N-vinyl pyrrolidone14 or vinyl acetate the VAc propagating radical, the RAFT agent should have an
(VAc)15,16 remains an important challenge. The reversible addi- efficient leaving group, with similar reactivity to the growing
tion–fragmentation chain transfer (RAFT) polymerization is macroradical towards the monomer addition. Most of the
considered a very effective RDRP method for the polymerization literature reports, concerning the xanthate mediated RAFT
of less activated monomers.12,17 Other RDRP methods mediated polymerization of VAc, refer the use of methyl(ethoxy carbonyl
by transition metal catalysts,18,19 iodine transfer11,20 or nitro- sulfanyl acetate) (Fig.
1
(Y1)),31–33 methyl 2-((ethox-
xides21 have been studied for vinyl chloride and VAc. Recently, ycarbonothiol)thio)propanoate (also known as O-ethyl-S-(1-
some authors reported the use of cobalt complex as organic methoxy carbonyl) ethyl dithiocarbonate), with 2-propionyl
metallic complexes for the controlled synthesis of poly(vinyl moiety as the leaving group (Fig. 1 (X1)), for either bulk,34
acetate) (PVAc).22–25 VAc stands out as one of the most studied solution35,36 or miniemulsion polymerizations,33 or very similar
non-activated vinyl monomers.26 PVAc has a wide range of RAFT agents.37,38 Nevertheless, other RAFT agents such as
industrial applications, from paints to coatings as well as its
a
´
Department of Chemical Engineering, University of Coimbra, Polo II, Rua Sılvio Lima,
3030-790 Coimbra, Portugal. E-mail: jcoelho@eq.uc.pt; Fax: +351 239 798 703; Tel:
+351 239 798 744
bDepartment of Radiology, University of Pennsylvania, Philadelphia, PA19104, USA
† Electronic supplementary information (ESI) available: Methods and
characterization details. See DOI: 10.1039/c5ra15580k
Fig. 1 Schematic representation of the most reported xanthates for
the RAFT polymerization of PVAc.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 91225–91234 | 91225

View Article Online
RSC Advances
Paper
dithiocarbamates have also been reported for the well-dened Fisher Chemical), ethyl acetate ($99.5%, Fisher Scientic),
polymerization of VAc.39,40
diethyl ether (99.85%, Fisher Scientic), hexane (99.05%, Fisher
The conjugation of polymers through a post polymerization Scientic), thionyl chloride ($99%, Sigma-Aldrich), propargyl
coupling strategy is also a powerful tool in macromolecular alcohol (PA) (99%, Aldrich), triethylamine ($99%, Sigma-
engineering to afford new block copolymers with segments that Aldrich), 2-bromopropionic acid ($99%, Aldrich), 5-trime-
are impossible to link by direct copolymerization. In fact, the thylsilyl-4-pentyn-1-ol (96%; Aldrich), N-(3-dimethylaminopropyl)-
single step synthesis of block copolymers is limited to few N0-ethylcarbodiimide hydrochloride ($99.0%, Sigma), 4-(dime-
monomers functionalities, usually with similar chemical and thylamino)pyridine ($99%, Aldrich), tetrabutyl ammonium
physical properties, or require the use of specic RAFT agents uoride trihydrate (TBAF$3H2O) (99%, Acros Organics), sodium
based on a switchable dithiocarbamate moiety that are able to azide (99%; Aldrich), tetrahydrofuran (THF) ($99.9%, Sigma-
mediate the polymerization of both activated and non-activated Aldrich), dimethylformamide (DMF) ($99.8%; Sigma-Aldrich),
monomers.41 In the case of non-activated monomers, where deuterated chloroform (CDCl3) ($99.8%, Euriso-top, +1% TMS)
controlled copolymerization is more difficult, reactions and deuterated DCM (CD2Cl2) ($99.6%, Euriso-top) were used as
inspired by the “click” coupling approach is a convenient received. Azido terminated-poly(ethylene glycol) (mPEG113-N3)
strategy to achieve new polymer architectures, otherwise diffi- was synthesized by a nucleophilic substitution of poly(ethylene
cult to access.42–44 The direct polymerization using a “clickable” glycol) methyl ether bromoisobutyrate (mPEG113-BiB) (previously
functionalized RAFT agent is a common strategy to afford synthesized according to the literature procedures49) using NaN3
polymers with a specic chain-end functionality, without the in DMF (procedure adapted from literature50) (see ESI† for
need of post-modication procedures.45 CuAAC reaction detailed synthesis).
between azide and alkyne chain-end functionalities is one of the
most explored “click” reaction.46 Stenzel and co-workers
reported the facile synthesis of poly(styrene)-b-PVAc block
Techniques
copolymers through a “click” coupling approach from a PVAc The 1H and 13C NMR spectra were recorded on a Bruker
synthesized using an azido-xanthate RAFT agent and DMX-360 (360 MHz for 1H NMR and 90 MHz for 13C NMR, with
poly(styrene) synthesized using one alkyne-dithiobenzoate a 5 mm manual switching QNP) and a Bruker Avance III
agent.45 A similar strategy was proposed, by the same group, for spectrometer (400 MHz, with a 5 mm TIX triple resonance
the synthesis of comb-like copolymers, from the reaction of an detection probe), in a deuterated solvent. Monomer conver-
azido functionalized linear PVAc with one alkyne modied sions were determined by integration of monomer and poly-
methacrylate monomer.47 The literature involving the use of mer peaks using MestRenova soware version: 6.0.2–5475.
xanthates with alkyne functionality is very scarce.
Fourier-transform infrared spectroscopy (FTIR) was performed
To the best of our knowledge, only one reference is available at 64 scans and with a 4 cmꢁ1 resolution between 500 and 3500
describing the synthesis of (S)-2-(propynyl propionate)-O-ethyl cmꢁ1, using a JASCO 4200 FTIR spectrometer, operating in the
xanthate, an alkyne terminated RAFT agent, for the controlled ATR mode (MKII GoldenGate™ Single Reexion ATR System).
synthesis of N-vinylpyrrolidone.48 The aim of the present study The thermogravimetric analysis (TGA) was carried out on a TGA
was to synthesize new efficient alkyne functionalized xanthate Q 500 machine (TA Instruments) with a heating ramp set at
RAFT agents, able to conduct controlled polymerization of vinyl a constant 10 ꢀC minꢁ1, and covering a temperature range from
acetate. The present strategy enabled the straightforward 25 to 300 ꢀC. High performance gel permeation chromatog-
preparation of PVAc block copolymers through a simple post raphy (HPSEC) was performed using a Viscotek (ViscotekTDA-
polymerization coupling method.
max) with a differential viscometer (DV), right-angle laser-light
scattering (RALLS, Viscotek), and refractive index (RI) detec-
tors, using column set of a PL 10 mm guard column followed by
one MIXED-E PLgel column and one MIXED-C PLgel column.
Experimental
Materials
Filtered THF was used as an eluent at a ow rate of 1 mL minꢁ1
ꢀ
Vinyl acetate (VAc) ($99%, Aldrich) was puried by passing the at 30 C. The samples were ltered through a polytetrauoro-
monomer through a basic alumina column and then distilled ethylene membrane with 0.2 mm pore before injection and the
under vacuum (bp 72–73 ꢀC). 2,20-Azobis(2-methylpropionitrile) system was calibrated with narrow PS standards. The dn/dc of
(AIBN) (98%, Fluka) was puried by recrystallization from PVAc in THF at 30 C was determined as 0.0581 (for l ¼ 670
ꢀ
methanol before use. 1,4-Dioxane (99.8%, Acros Organics) was nm) using a RUDOLPH RESEARCH J357 Automatic Refrac-
passed through alumina column to remove peroxides and tometer (J357-NDS-670-CC). Molecular weight (Mn,GPC) and
distilled under reduced pressure prior to use. Poly(ethylene dispersity (Đ) of synthesized polymers were determined by
glycol) methyl ether (mPEG113, MW ¼ 5000 Da) (Aldrich) was using either a universal calibration or multidetector analysis
dried by azeotropic distillation with toluene. Sodium ascorbate (OmniSEC soware version: 4.6.1.354). Ultraviolet-Visible (UV-
(NaAsc) ($98%, Sigma), copper(II) sulfate pentahydrate Vis) spectroscopy was carried out using a Jasco V-530 spectro-
(CuSO4$5H2O) ($98%, Aldrich), methyl 2-bromopropionate photometer. The analyses were carried out in CHCl3 in the 250–
(98%, Aldrich), methanol (99.9%, Fisher Scientic), dichloro- 400 nm range at 25 ꢀC. Absorption spectra were measured from
methane (DCM) (99.99%, Fisher Scientic), potassium ethyl 250 to 400 nm with a resolution of 2.0 nm in a 10 mm UV-
xanthogenate (96%; Aldrich) anhydrous sodium sulfate ($98%, cuvette.
91226 | RSC Adv., 2015, 5, 91225–91234
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
chromatography on silica starting with hexane and then
hexane/ethyl acetate (10 : 1 vol%) as the eluent to give AT-X1 as
a yellow liquid (2.64 g, 54%). 1H NMR (360 MHz, CDCl3):
d (ppm) 4.7335 (d, 1H, 4JHH ¼ 2.4 Hz, diastereotopic ^C–CHH–
Procedures
Synthesis of (RS)-O-ethyl-S-(1-methoxycarbonyl) ethyl-
dithiocarbonate (X1). Methyl 2-bromopropionate (5.13 g,
30.73 mmol) was dissolved in 100 mL of methanol and the
solution was cooled down in an ice bath. Potassium ethyl xan-
thogenate (5.74 g, 34.38 mmol) was then slowly added over
a period of 30 minutes. Aer the complete dissolution of the
salt, the reaction mixture was stirred at room temperature
during 24 h. The KBr formed was ltered under vacuum, the
product was extracted with an ether/hexane mixture (2 : 1 vol%),
washed three times with water and dried over anhydrous
sodium sulfate. The solvent was evaporated at reduced pressure
to give a yellow liquid that was further puried by column
chromatography on silica with hexane/ethyl acetate
(10 : 1 vol%) as the eluent to give X1 (4.30 g, 67%). 1H NMR
4
O), 4.7321 (d, 1H, JHH ¼ 2.4 Hz, diastereotopic ^C–CHH–O),
4.6310 (q, 1H, 3JHH ¼ 7.1 Hz, diastereotopic CHH–CH3), 4.6302
3
(q, 1H, JHH ¼ 7.1 Hz, diastereotopic CHH–CH3), 4.41 (q, 1H,
3JHH ¼ 7.4 Hz, CH–CH3), 2.49 (t, 1H, 4JHH ¼ 2.4 Hz, CH^C), 1.58
(d, 3H, 3JHH ¼ 7.4 Hz, CH3–CH), 1.41 (t, 3H, 3JHH ¼ 7.1 Hz, CH3–
CH2). 13C NMR (90 MHz, CDCl3): d (ppm) 211.69 (C]S), 170.79
(C]O), 77.16 (^C–), 75.46 (HC^), 70.44 (CH2–CH3), 53.13
(CH2–O), 46.83 (CH–CH3), 16.68 (CH3–CH), 13.73 (CH3–CH2)
(the peak at 77.16 ppm is overlapped with the solvent peak). 13
C
NMR (90 MHz, CD2Cl2): (ppm) 212.14 (C]S), 171.12 (C]O),
77.74 (^C–), 75.64 (HC^), 71.14 (CH2–CH3), 53.54 (CH2–O),
47.14 (CH–CH3), 16.96 (CH3–CH), 13.97 (CH3–CH2).
Synthesis of protected alkyne-terminated RAFT agent (PAT-
X1)
3
(360 MHz, CDCl3): d (ppm) 4.6232 (q, 1H, JHH ¼ 7.14 Hz, dia-
3
stereotopic –OCHHCH3), 4.6199 (q, 1H, JHH ¼ 7.1 Hz, diaster-
3
eotopic –OCHHCH3), 4.36 (q, 1H, JHH ¼ 7.4 Hz, –CH), 3.73 (s,
2-(Ethoxycarbonothioylthio)propanoic acid. 4.18 g (27.30 mmol)
of 2-bromopropionic acid was dissolved in 40 mL of dry
methanol. The solution was cooled down in an ice bath. Potas-
sium ethyl xanthogenate 5.126 g (31.98 mmol) was slowly added
to the methanol solution, in portions, over a period of 30 min.
Aer the complete dissolution of potassium ethyl xanthogenate,
the ice bath was removed and the reaction proceeded at room
temperature for 24 h. The reaction by-product, KBr, was ltered
under reduced pressure and the product extracted with an ether/
hexane mixture (2 : 1 vol%), washed three times with water and
dried over anhydrous sodium sulfate. The product was obtained
aer the solvent evaporation at reduced pressure. 1H NMR
(400 MHz, CDCl3): d (ppm) 10.00 (s, 1H, –OH), 4.6419 (q, 1H,
3H, –CH3), 1.56 (d, 3H, 3JHH ¼ 7.4 Hz, –CHCH3), 1.40 (t, 3H, JHH
¼ 7.14 Hz, –CH2CH3).
Synthesis of alkyne-terminated RAFT agent, O-ethyl-S-(1-
propargoxycarbonyl) ethyl-dithiocarbonate (AT-X1)
2-Bromopropionyl chloride. 4.00 mL of thionyl chloride
(5.14 mmol) was slowly added to 4.50 mL of 2-bromopropionic
acid (50.00 mmol). A small amount of DMF (10 mL) was used to
catalyze the reaction. The mixture was heated to 80 ꢀC and
stirred until the complete release of gaseous by-products of the
reaction. The product was used without any further purication
steps.
(RS)-Propargyl 2-bromopropionate. A solution of PA (2.80 g,
50.00 mmol) and triethylamine (5.06 g, 50.00 mmol) in DCM
3JHH ¼ 7.1 Hz, diastereotopic CHH–CH3), 4.6399 (q, 1H, 3JHH
¼
ꢀ
was cooled down to ꢂꢁ20 C with liquid nitrogen. The 2-bro-
3
7.1 Hz, diastereotopic CHH–CH3), 4.41 (q, 1H, JHH ¼ 7.47 Hz,
mopropionyl chloride was added in portions to the solution.
The solution was le off from the cold and kept under stirring
until reach the room temperature. The product was washed
three times with water and the organic phase was dried under
anhydrous sodium sulfate. Aer solvent evaporation the
product was obtained as a light yellow oil (6.98 g, 73%). 1H NMR
3
–CH–CH3), 1.60 (d, 3H, JHH ¼ 7.4 Hz, –CH3–CH), 1.41 (t, 3H,
3JHH ¼ 7.1 Hz, –CH3–CH2).
PAT-X1. In a 200 mL ask, the 2-(ethoxycarbonothioylthio)
propanoic acid (0.60 g, 3.10 mmol) was dissolved in 60 mL of
dry DCM. 5-Trimethylsilyl-4-pentyn-1-ol (0.68 mL, 3.74 mmol)
was added and the mixture was cooled down to 0 ꢀC and
bubbled with argon. N-(3-Dimethylaminopropyl)-N0-ethyl-
carbodiimide hydro-chloride (0.78 g, 4.09 mmol) and 4-(dime-
thylamino)pyridine (5.76 mg, 0.05 mmol) were then added to
the solution and the mixture was stirred in the ice bath for more
30 min. The reaction was le at room temperature for 24 h. The
RAFT agent was puried by column chromatography on silica
with hexane/ethyl acetate (10 : 1 vol%) as the eluent. The PAT-X1
was obtained as a yellow oil (0.89 g, 86.6%). 1H NMR (400 MHz,
CDCl3): d (ppm) 4.64 (q, 2H, 3JHH ¼ 7.12 Hz; CH2–CH3), 4.38 (q,
1H, 3JHH ¼ 7.30 Hz, –CH–CH3), 4.23 (t, 2H, 3JHH ¼ 6.28 Hz; CH2–
4
(360 MHz, CDCl3): d (ppm) 4.7599 (d, 1H, JHH ¼ 2.5 Hz, dia-
4
stereotopic HC^C–CHHO–), 4.7524 (d, 1H, JHH ¼ 2.5 Hz,
3
diastereotopic HC^C–CHHO–), 4.39 (q, 1H, JHH ¼ 6.9 Hz,
–CH–Br), 2.5 (t, 1H, JHH ¼ 2.5 Hz, HC^C–), 1.82 (d, 3H, 3JHH
¼
6.9 Hz, –CH3). 13C NMR (90 MHz, CDCl3): d (ppm) 169.48 (C]
O), 76.86 (^C–), 75.74 (HC^), 53.40 (CH2–O), 39.30 (CH–Br),
21.58 (Br–CH3).
AT-X1. Propargyl 2-bromopropionate (4.04 g, 21.13 mmol) was
dissolved in 25 mL of PA and the solution was cooled down in
an ice bath. Potassium ethyl xanthogenate (3.84 g, 23.92 mmol)
was then added to the solution in portions over a period of
30 minutes. Aer the complete dissolution of the salt, the
reaction mixture was stirred at room temperature overnight.
The solid KBr was ltered off, the ltrate was extracted with
ether/hexane (2 : 1 vol%) and the extract was washed three
times with water (500 mL) and dried over anhydrous sodium
sulfate. The solvent was evaporated at reduced pressure to give
O), 2.33 (t, 2H, 3JHH ¼ 7.05 Hz; C^C–CH2–), 1.87 (m, 2H, 3JHH
¼
6.66 Hz; –CH2–), 1.57 (d, 3H, 3JHH ¼ 7.14 Hz, –CH3–CH), 1.42 (t,
3H, 3JHH ¼ 7.13 Hz, –CH3–CH2), 0.14 (s, 9H, (CH3)3–Si). 13C NMR
(90 MHz, CDCl3) d (ppm) 212.22 (C]S), 171.48 (C]O), 105.60
(^C–O), 85.63 (Si–C^), 70.41 (CH2–CH3), 64.45 (CH2–O), 47.33
(CH–CH3), 27.71 (CH2–CH2–CH2), 17.01 (^C–CH2–), 16.65
(CH3–CH), 13.83 (CH3–CH2), 0.22 ((CH3)3).
a
yellow liquid that was further puried by column
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 91225–91234 | 91227

View Article Online
RSC Advances
Paper
Aer 72 h of reaction, a sample was collected and analyzed by
GPC.
Typical procedure for PVAc deprotection. A solution of pure
protected alkyne terminated PVAc (PAT–PVAc) (Mn,GPC ¼ 6.0 ꢃ
103, Đ ¼ 1.36), (0.25 g, 4.20 ꢃ 10ꢁ2 mmol) in THF (10 mL) was
bubbled with nitrogen for about 10 minutes and then cooled
down to ꢁ20 ꢀC. Then, 2.14 mL of a 0.2 M solution of
TBAF$3H2O (0.43 mmol) was slowly added to the polymer solu-
tion. Aer stirring for 30 minutes at low temperature, the reac-
tion proceeded over night at ambient temperature. The reaction
mixture was passed through a silica column to remove the excess
of TBAF and the polymer was recovered by precipitation in cold
hexane, dried under vacuum and analyzed by 1H NMR.
Coupling reaction between alkyne-terminated PVAc and N3-
PEG. The alkyne-terminated PVAc obtained aer the depro-
tection of the PAT–PVAc (50 mg, 8.33 mmol) and N3-PEG (55 mg,
10.8 mmol) were dissolved into 5 mL of THF. The mixture was
placed in a round-bottom ask equipped with a magnetic stir
bar and sealed with a rubber septum. A stock solution of
sodium ascorbate (40 mM; 250 mL) in deionized water was
added to the solution and the mixture was bubbled with
nitrogen for 20 min to remove oxygen. Lastly, a degassed stock
solution of CuSO4$5H2O (13 mM; 250 mL) in deionized water
was injected into the ask under nitrogen atmosphere. The
reaction was allowed to proceed under stirring at 40 ꢀC for 48 h.
The nal mixture was passed through an alumina column to
remove the copper catalyst and the product precipitated into
cold hexanes. The product was analyzed by GPC and FTIR-ATR
spectroscopy in order to conrm the success of the coupling
reaction.
Fig.
2 Structures of RAFT agents synthesized: O-ethyl-S-(1-
methoxycarbonyl) ethyl-dithiocarbonate (X1), alkyne-terminated RAFT
agent (AT-X1) and protected alkyne-terminated RAFT agent (PAT-X1).
Typical procedure for the RAFT polymerization of the VAc
with [VAc/X1/AIBN] ¼ 100 : 1 : 0.2 in 1,4-dioxane. VAc (2.02 g,
23.49 mmol), X1 (48.47 mg, 0.23 mmol), AIBN (7.82 mg, 0.05 mg)
and 1.4-dioxane (1.93 mL; previously bubbled with nitrogen for
about 10 min) were placed into a 25 mL Schlenk reactor. The
reactor was sealed, frozen in liquid nitrogen, and the mixture
was deoxygenated with four freeze–vacuum–thaw cycles and
purged with nitrogen. The Schlenk reactor was placed in an oil
bath at 60 ꢀC with stirring (500 rpm). Different reaction mixture
samples were collected during the polymerization through an
airtight syringe, purging the side arm of the Schlenk reactor
with nitrogen. The collected samples were analyzed by 1H NMR
spectroscopy to calculate the monomer conversion and theo-
retical molecular weight (Mn,th), and by GPC to determine
Mn,GPC and Đ of the polymers. The other RAFT polymerizations
were carried out employing the same procedure described but
using AT-X1 or PAT-X1 as the RAFT agents.
Results and discussion
Synthesis of the RAFT agents
Typical procedure for the chain extension of PVAc. A sample
of protected alkyne-terminated PVAc (PAT–PVAc) (Mn,GPC ¼ 3.01
ꢃ 103, Đ ¼ 1.20) synthesized through a typical RAFT polymeri- The use of functionalized RAFT agents avoids further steps
zation using the PAT-X1, and puried by precipitation in cold involving the modication of the terminals in the polymeric
hexane, was used as macro-RAFT agent in a new RAFT poly- chain structures with chemical groups suitable for further
merization. Briey, PAT–PVAc (31.8 mg, 13.4 mmol) was dis- reactions, namely reactions inspired by the “click” coupling
solved in 1,4-dioxane (7 mL) and placed into a Schlenk reactor. strategies. Two different RAFT agents for the polymerization of
360 mL of a stock solution of AIBN (1.1 mg, 6.64 mmol) in 1.4-
dioxane was added to the reactor followed by the addition of
VAc (4 mL, 46.46 mmol). The reactor was sealed, frozen in liquid
nitrogen, and the mixture was deoxygenated with four freeze–
vacuum–thaw cycles and purged with nitrogen. The Schlenk
reactor was placed in an oil bath at 60 ꢀC with stirring (500 rpm).
Fig. 3 Schematic representation of the synthesis strategy of alkyne- Fig. 4 1H NMR spectrum in CDCl3 of alkyne-terminated RAFT agent (AT-
terminated RAFT agent (AT-X1).
X1).
91228 | RSC Adv., 2015, 5, 91225–91234
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
Fig. 5 Schematic representation of the synthesis strategy of protected
alkyne-terminated RAFT agent (PAT-X1).
Fig. 7 (a) Kinetic plots of conversion and ln[M]0/[M] vs. time and (b)
plot of number average molecular weights (Mn,GPC) and dispersity (Đ)
vs. conversion (%) (the dashed line represents the theoretical molec-
ular weight at a given conversion) for RAFT of VAc at 60 ꢀC in 1,4-
dioxane using X1. Reaction conditions: [VAc]0/[1,4-dioxane]0 ¼ 1/1
(w/w); [VAc]0/[X1]0/[AIBN]0 ¼ 100/1/0.2 (molar).
non-activated monomers were synthesized (AT-X1 and PAT-X1),
based on O-ethyl-S-(1-methoxycarbonyl) ethyl-dithiocarbonate
xanthate (X1).34–36 The structures of the RAFT agents are present
in Fig. 2.
X1 was synthesized through the reaction of potassium ethyl
xanthogenate with methyl 2-bromopropionate in methanol
according to the similar procedures reported in literature for
analogous RAFT agents.51,52 The success of the reactions was
1
conrmed by H NMR (ESI, Fig. S1†). Although the impurities
aer the synthesis are very small, the purication procedures
are crucial to avoid RAFT agent contaminations that could
interfere with the success of polymerization.
The synthesis of the AT-X1 was already been reported by Patel
and co-authors for the polymerization of N-vinylpyrrolidone.48
However, the method reported here is easier, cleaner and
more efficient than the aforementioned method that involves
the carbodiimide activation. The synthesis of AT-X1 was carried
out into two steps; rstly, the synthesis of the alkyne terminated
bromide through the reaction of 2-bromopropionyl chloride
and propargyl alcohol (PA), followed by the bromine substitu-
tion with the potassium ethyl xanthogenate (Fig. 3). The success
of the reaction was conrmed by 1H and 13C NMR spectroscopy
(Fig. 4, S2 and S3 (ESI)†). The FTIR-ATR spectra of the AT-X1
(Fig. S4, ESI†) shows the presence of the characteristic alkyne
Fig. 8 (a) Kinetic plots of conversion and ln[M]0/[M] vs. time and (b)
plot of number average molecular weights (Mn,GPC) and dispersity (Đ)
vs. conversion (%) (the dashed line represents the theoretical molec-
ular weight at a given conversion) for RAFT of VAc at 60 ꢀC in
1,4-dioxane using AT-X1. Reaction conditions: [VAc]0/[1,4-dioxane]0
1/1 (w/w); [VAc]0/[AT-X1]0/[AIBN]0 ¼ 100/1/0.2 (molar).
¼
It is known that the alkyne group in the RAFT agent may
interfere with the radical polymerization process.45 In order to
evaluate this possibility, the synthesis of new protected RAFT
agent (protected alkyne-terminated RAFT agent (PAT-X1)) using
a trimethyl silyl group was envisaged. For the synthesis of the
PAT-X1, 2-(ethoxycarbonothioylthio)propanoic acid, was rstly
synthesized through the reaction of potassium ethyl xan-
thogenate and 2-bromopropionic acid in methanol. The further
coupling reaction with 5-trimethylsilyl-4-pentyn-1-ol originates
PAT-X1 (Fig. 5). The success of the reaction was conrmed by 1H
C^H stretch vibration at 3300 cmꢁ1 47 and also –C]S and C–S
,
stretching vibrations at 1044 cmꢁ1 and 633 cmꢁ1, respectively.
13
NMR (Fig. 6) and C NMR (ESI Fig. S5†) (‡53–55).
‡ It should be noted that all three target molecules contain a chiral center
C*HMeS(CO). It makes geminal methylene protons CHH diastereotopic and
causes anisochrony due to unequal magnetic eld sensed by these nuclei. The
resonance signals of these protons are overlapped in the spectrum of PAT-X1,
whereas the 1H NMR spectra of X1 and AT-X1 revealed resolved peaks of each
such proton. Therefore, the difference in chemical shis for these anisochronic
protons is 0.0135 ppm for –OCHHCH3 in X1, 0.0014 ppm for CH^C–CHHO–
and 0.0009 ppm for –OCHHCH3 in AT-X1. Interestingly, the chemical shi
difference of 0.0075 ppm for CH^C–CHHO– diastereotopic protons in
Fig. 6 1H NMR spectrum in CDCl3 of protected alkyne-terminated
propargyl 2-bromopropionate is almost equal to JHH coupling constant, thus
4
RAFT agent (PAT-X1).
making a quasitriplet from the two doublets (ESI).
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 91225–91234 | 91229

View Article Online
RSC Advances
Paper
good results obtained when X1 was used (Fig. 7), the polymer
does not have the necessary functionality that would allow
further coupling reactions with other molecules or polymers. In
the case of X1, polymer post-modication reactions would be
required in order to achieve a specic functionality in the
polymer chain-end. In this context, the concept of the direct
introduction of the desired functionality in the RAFT agent is
preferable.
The kinetic data presented in Fig. 7 for the RAFT agent X1
reveals that the polymer Mn increases linearly with monomer
conversion and Đ remain below 1.4 throughout the polymeri-
zation. The obtained values are in accordance with similar
literature reports for xanthate mediated RAFT polymerizations
of Vac in bulk32 or in ethyl acetate.35,36
The AT-X1 and PAT-X1 are xanthate molecules with similar
structure to X1 but with a slight variation of the end-group
functionality of the leaving group (R group). The protection of
the alkyne moiety (PAT-X1) was performed in order to observe
the role of the terminal alkyne in the polymerization course. It is
known that the alkyne hydrogen in the end of the leaving group
of the RAFT agent may interfere with the radical polymeriza-
tion.45 In fact, when X1 was replaced by AT-X1, using similar
reaction conditions, the homopolymerization of VAc was
slower, and larger Đ were observed, as shown in the kinetic data
presented in Fig. 8 and GPC traces in Fig. S6 (ESI†).
Fig. 9 (a) Kinetic plots of conversion and ln[M]0/[M] vs. time and (b)
plot of number average molecular weights (Mn,GPC) and dispersity (Đ)
vs. conversion (%) (the dashed line represents the theoretical molec-
ular weight at a given conversion) for RAFT of VAc at 60 ꢀC in
1,4-dioxane using PAT-X1. Reaction conditions: [VAc]0/[1,4-dioxane]0
¼ 1/1 (w/w); [VAc]0/[PAT-X1]0/[AIBN]0 ¼ 100/1/0.2 (molar).
Polymerization of VAc using the synthesized RAFT agents
To investigate the ability of the RAFT agents to control the
polymerization of non-activated monomers, VAc was used as
a model monomer. The polymerization of VAc was carried out
using the different xanthates in 1,4-dioxane ([1,4-dioxane]0/
[VAc]0 ¼ 1/1 (w/w)) at 60 ꢀC and initiated by the AIBN. The ratio
of RAFT agent : AIBN was kept at 1 : 0.2. Monomer conversions
1
were calculated using H NMR spectroscopy by comparing the
Fig. 9 presents the kinetic data obtained for the homo-
polymerization of VAc using the protected-alkyne RAFT agent.
The rst-order kinetic and the linear evolution of the MW with
the conversion indicate a controlled polymerization. It is
interesting to notice that below 70% conversion, the Đ values
are very low for a non-activated monomer such as VA (Đ < 1.2),
but tend to increase for high monomer conversions. For
conversions above 80%, the Mn,GPC values become smaller than
Mn,th. This observation may be ascribed to irreversible transfer
reactions, chain transfer reactions to monomer and polymer,
due to the very reactive nature of the VAc propagating radical.56
This effect is mostly detected in the polymer GPC traces by the
presence of a prominent low MW tail (high retention volume)
(Fig. 10) and consequent broad MW distributions from
moderate to higher monomer conversions. Similar results were
already reported for similar RAFT polymerization of VAc (bulk,
60 ꢀC).57,58 It should be noted the presence of an induction
period for the different RAFT agents studied, which could be
related with slower reinitiation of the initial RAFT agent.59
Moreover, several literature reports dealing with the xanthate
mediated RAFT polymerization of PVAc reported a similar
integrations of the –CH signals on the VAc (d ¼ 4.50 ppm) with
the corresponding signals of the polymer backbone (d ¼ 4.80).
X1 was used for comparison purposes, since it was already re-
ported for the synthesis of well-dened PVAc.34–36 Despite the
Fig. 10 Evolution of the GPC traces with conversion for the RAFT
polymerization of VAc in 1,4-dioxane at 60 ꢀC in the presence of the
PAT-X1. Reaction conditions: [VAc]0/[1,4-dioxane]0
[VAc]0/[PAT-X1]0/[AIBN]0 ¼ 100/1/0.2 (molar).
¼
1/1 (w/w);
Table 1 Kinetic parameters for the RAFT polymerization of VAc using the X1, AT-X1 or PAT-X1 in 1,4-dioxane. Reaction conditions: [VAc]0/[1,4-
dioxane] ¼ 1/1 (w/w); [VAc]0/[RAFT agent]0/[initiator]0 ¼ 100/1/0.2
Timea ,h
Conv.a, %
kappp, hꢁ1
Mn,th ꢃ 103
Mn,GPC ꢃ 103
Đa
a
a
Entry
RAFT agent
Initiator
Temp., ꢀC
1
2
3
4
X1
AIBN
AIBN
AIBN
AIBN
60
60
60
60
24
24
32
16
98
90
96
—
0.291
0.118
0.182
—
8.7
8.0
8.52
—
6.80
6.0
6.69
6.06
1.4
2.0
1.6
2.2
AT-X1
PAT-X1
—
a
Values obtained from the last sample from the kinetic study.
91230 | RSC Adv., 2015, 5, 91225–91234
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
observation.60,61 Even so, for our novel PAT-X1, the observed
induction period is much smaller. In all cases, the molar mass
evolution plots show a discrepancy between the values of Mn,th
and Mn,GPC, increasing with conversion. This result may be
related with the high concentration of initiator used, which
consequently increases the concentration of radicals in the
system and promotes irreversible termination reactions. The
summary of all experiments performed using the three different
RAFT agents is shown in Table 1. The results suggest that only
the RAFT agents X1 and PAT-X1 were able to conduct
a controlled polymerization of VAc with relatively narrow MW
distributions, up to high conversions. Despite the high Đ value
obtained for the last kinetic point using PAT-X1, in comparison
with the X1, the kinetic results present in Fig. 9 and 10, indicate
that the Đ values tend to increase with reaction conversion. The
broad MW distribution observed for the reactions with the
alkyne functionalized RAFT agent (AT-X1) prove the inefficiency
of such compound to conduct a controlled polymerization of
VAc. On this matter, the Đ values of the PVAc synthesized
through RAFT using AT-X1 or using FRP conditions are similar
(Đ ¼ 2.2).
Fig. 12 The 1H NMR spectrum of PVAc synthesized by RAFT using
PAT-X1 (Mn,GPC ¼ 6.0 ꢃ 103; Mn,NMR ¼ 7.56 ꢃ 103, Đ ¼ 1.36) in CDCl3.
PVAc chain-end functionality
The chemical structure of the PVAc synthesized by RAFT poly-
merization was determined with 1H NMR, FTIR-ATR and UV-Vis
analysis. Fig. 12 shows the 1H NMR spectrum of a PVAc sample
synthesized using the PAT-X1. The characteristic peaks of the
PVAc structure at 1.75 ppm (o, o0, –CH2–CH–), 2.02 ppm (n, n0,
–CH3), 4.86 ppm (m, –CH2–CH–) and 6.62 ppm (m0, –CH2–CH–S)
are in agreement with the data reported in the literature.37 The
retention of RAFT functionality is evidenced by the peaks from
the PAT-X1 at 0.14 ppm (k, –Si(CH3)3–), 0.88 ppm (a, –CH2–CH3),
1.17 ppm (d, –CH–CH3), 2.31 ppm (j, C^C–CH2), 3.74 ppm (b,
–CH2–CH3), 4.07 ppm (c, –CH–CH3) and 4.15 ppm (h, –CH2–O–).
It should be noted that the ratio between the integral of k and
a signals does not correspond to the theoretical value assuming
the number of protons from the R and Z groups, respectively.
This result may be justied by the unavoidable termination
reactions that occur in any radical based polymerization
method. It should not be excluded also a possible loss of RAFT
chain end functionality during the purication steps.
Thermogravimetric analysis of the RAFT agents
The thermal behavior of RAFT agents was analyzed by TGA
(Fig. 11). The results reveal a single step of mass loss, at rela-
tively low temperatures, for the different RAFT agents synthe-
sized. In order to evaluate the nature of this event, a preparative
experiment in a sealed ask under nitrogen was carried out, at
1
ꢀ
130 C during 2 h. The comparison of H NMR spectra of the
RAFT agent before and aer the thermal treatment has shown
no differences on the peak integrations, which indicates that
the mass loss observed in TGA traces are related to volatiliza-
tion. No signicant mass loss was observed aer the experi-
ment. Regarding the effect of the structure of R group, the
results suggest that the volatilization temperature increases
with the following order: PAT-X1 > AT-X1 > X1.
The preservation of the terminal chains ends during the
RAFT reaction can also be accessed by FTIR-ATR analysis. The
FTIR-ATR spectra of the PAT-X1 and the PVAc synthesized using
Fig. 11 TGA weight loss curves of X1, AT-X1 and PAT-X1, obtained at
a heating rate of 10 ꢀC minꢁ1
.
Fig. 13 FTIR-ATR spectra of PAT-X1 and PAT–PVAc.
RSC Adv., 2015, 5, 91225–91234 | 91231
This journal is © The Royal Society of Chemistry 2015

View Article Online
RSC Advances
Paper
Fig. 14 The GPC traces of PAT–PVAc samples before (on the right)
and after chain extension (on the left) experiment.
Fig. 16 GPC traces of the RALS signal of the PVAc and PVAc-b-PEG
copolymer, after the coupling reaction.
the PAT-X1 is shown in Fig. 13. The bands at 2850–2940 cmꢁ1
are associated to both symmetric and asymmetric C–H
stretching vibrations. A strong absorption band at 1740 cmꢁ1 is
related with the –C]O stretching vibration (carbonyl bond of
the ester). The characteristic bands of the xanthate group,
–C]S and C–S, at 1044 cmꢁ1 and 633 cmꢁ1 respectively and the
characteristic bands of the trimethylsilyl group (–Si–(CH3)3), at
755 cmꢁ1 and 840 cmꢁ1 are present in both FTIR-ATR spectra.
Ultraviolet-Visible (UV-Vis) spectroscopy has been used as an
efficient tool to identify the presence of the characteristic –C]S
end-group of polymers prepared by RAFT polymerization. The
polymer Z-group can be lost during the polymerization process
due to side reactions of the thiocarbonyl groups or due to the
inherent termination reactions that occurs during the poly-
merization.62 The UV-Vis spectra in CHCl3 of all synthesised
PVAc are presented in ESI (Fig. S7†). All samples show an
absorption band below 300 nm ascribed to the thiocarbonyl
bound, indicating the presence of such groups in the nal
polymer backbone. This thiocarbonyl group can be further
removed or transformed in order to achieve a desired func-
tionality and easily conjugate the polymer with other molecules
or polymer segments.63,64
Chain extension reaction
The PVAc synthesized through RAFT polymerization (Mn,GPC
¼
3.01 ꢃ 103, Đ ¼ 1.20) was puried and used as macro-RAFT
agent. Fig. 14 shows the complete shi of the molecular weight
distribution from a PVAc macroinitiator (macro PAT–PVAc) to
a higher MW values (extended PVAc, Mn,GPC ¼ 10.64 ꢃ 103, Đ ¼
1.88) conrming the “living” nature of the polymer.
Deprotection of PVAc and coupling reaction with N3-PEG
Aer the RAFT polymerization of VAc using the PAT-X1, the
protective trimethyl silyl group was removed using TBAF (Fig. 15
(1.2)). The success of the reaction was conrmed by the disap-
pearance of the characteristic trimethyl silyl signal (k) at
0.14 ppm by the 1H NMR spectrum of the unprotected PVAc
(Fig. 12 (k) and S8, ESI†).
As a proof of concept an azide terminated PEG (N3-PEG) was
used for the post-polymerization coupling reaction with an
alkyne-terminated PVAc (Fig. 15 (1.3)). In fact, this reaction
could not be named as “click” reaction since it did not fulll all
of the criteria in the context of macromolecular chemistry.65 The
success of the synthesis of the PEG-b-PVAc copolymer was
evaluated by GPC and FTIR-ATR spectroscopy. Fig. 16 shows the
Fig. 15 Schematic representation of the RAFT polymerization of VAc (1.1), PVAc deprotection (1.2) and synthesis of PEG-b-PVAc block
copolymers by CuAAC reaction (1.3).
91232 | RSC Adv., 2015, 5, 91225–91234
This journal is © The Royal Society of Chemistry 2015

View Article Online
Paper
RSC Advances
clear shi of the molecular weight distribution of the PVAc
block towards higher molecular weight values. It should be
stressed the presence of a shoulder that based on the GPC traces
can be ascribed to the some unreacted PVAc segments. More-
over, the comparison of FTIR-ATR spectra of the homopolymer
precursors, N3-PEG and AT-PVAc with the copolymer PEG-b-
PVAc (Fig. S9, ESI†), conrms the presence of the characteristic
bands from each homopolymer segment in the spectrum of the
7 C. M. R. Abreu, A. C. Serra, A. V. Popov, K. Matyjaszewski,
T. Guliashvili and J. F. J. Coelho, Polym. Chem., 2013, 4,
5629–5636.
8 J. R. Gois, D. Konkolewic, A. V. Popov, T. Guliashvili,
K. Matyjaszewski, A. C. Serra and J. F. J. Coelho, Polym.
Chem., 2014, 5, 4617–4626.
9 T. Guliashvili, P. V. Mendonca, A. C. Serra, A. V. Popov and
J. F. J. Coelho, Chem.–Eur. J., 2012, 18, 4607–4612.
copolymer and reveals the disappearance of the characteristic 10 P. V. Mendonca, A. C. Serra, J. F. J. Coelho, A. V. Popov and
azide signal at 2100 cmꢁ1, conrming the success of the
coupling reaction.
T. Guliashvili, Eur. Polym. J., 2011, 47, 1460–1466.
11 V. Percec, A. V. Popov, E. Ramirez-Castillo, J. F. J. Coelho and
L. A. Hinojosa-Falcon, J. Polym. Sci., Part A: Polym. Chem.,
2004, 42, 6267–6282.
12 C. M. R. Abreu, P. V. Mendonça, A. C. Serra, J. F. J. Coelho,
A. V. Popov, G. Gryn’ova, M. L. Coote and T. Guliashvili,
Macromolecules, 2012, 45, 2200–2208.
13 Y. Piette, A. Debuigne, C. Jerome, V. Bodart, R. Poli and
C. Detrembleur, Polym. Chem., 2012, 3, 2880–2891.
14 I. J. Johnson, E. Khosravi, O. M. Musa, R. E. Simnett and
A. M. Eissa, J. Polym. Sci., Part A: Polym. Chem., 2015, 53,
775–786.
Conclusions
We reported the synthesis of one protected alkyne containing
xanthate RAFT agent, able to efficiently control the polymeri-
zation of VAc. The protection of the alkyne moiety in the RAFT
agent is crucial to afford a polymerization with a good control
over the MW and with low Đ. The structural analysis of the
PVAc, performed by 1H NMR, FTIR-ATR and UV-Vis experiments
reveal the retention of the chain-end functionality. The “living”
nature of the PVAc synthesized through RAFT was conrmed by
a successful chain extension experiment. Aer the deprotection
of the alkyne end group, the well-dened alkyne-terminated
PVAc can be easily conjugated with azido-terminated structures
through a CuAAC reaction.
15 M. C. Iovu and K. Matyjaszewski, Macromolecules, 2003, 36,
9346–9354.
16 V. Percec, T. Guliashvili, J. S. Ladislaw, A. Wistrand,
A. Stjerndahl, M. J. Sienkowska, M. J. Monteiro and
S. Sahoo, J. Am. Chem. Soc., 2006, 128, 14156–14165.
17 S. Harrisson, X. Liu, J.-N. Ollagnier, O. Coutelier, J.-D. Marty
and M. Destarac, Polymers, 2014, 6, 1437.
Acknowledgements
18 J. P. Mendes, F. Branco, C. M. R. Abreu, P. V. Mendonça,
A. C. Serra, A. V. Popov, T. Guliashvili and J. F. J. Coelho,
ACS Macro Lett., 2014, 3, 858–861.
´
Joana R. Gois acknowledges FCT-MCTES for her PhD scholar-
ship (SFRH/BD/69635/2010). The NMR data was collected at the
UC-NMR facility which is supported in part by FEDER – Euro-
pean Regional Development Fund through the COMPETE Pro-
gramme (Operational Programme for Competitiveness) and by
National Funds through FCT – Fundaçao para a Ciencia e
a Tecnologia (Portuguese Foundation for Science and Tech-
nology) through grants REEQ/481/QUI/2006, RECI/QEQ-
QFI/0168/2012, CENTRO-07-CT62-FEDER-002012, and Rede
19 T. Huadong, R. Maciej and S. Youqing, in Controlled/Living
Radical Polymerization: Progress in ATRP, American
Chemical Society, 2009, vol. 1023, ch. 10, pp. 139–157.
20 V. Percec, A. V. Popov, E. Ramirez-Castillo and J. F. J. Coelho,
J. Polym. Sci., Part A: Polym. Chem., 2005, 43, 773–778.
21 D. Braun, J. Vinyl Addit. Technol., 2005, 11, 86–90.
22 C.-H. Peng, J. Scricco, S. Li, M. Fryd and B. B. Wayland,
Macromolecules, 2008, 41, 2368–2373.
˜
ˆ
ˆ
´
Nacional de Ressonancia Magnetica Nuclear (RNRMN).
23 Y.-C. Lin, Y.-L. Hsieh, Y.-D. Lin and C.-H. Peng,
Macromolecules, 2014, 47, 7362–7369.
24 A. Kermagoret, Y. Nakamura, M. Bourguignon,
Notes and references
´ ˆ
C. Detrembleur, C. Jerome, S. Yamago and A. Debuigne,
1 P. J. Roth, C. Boyer, A. B. Lowe and T. P. Davis, Macromol.
Rapid Commun., 2011, 32, 1123–1143.
ACS Macro Lett., 2014, 3, 114–118.
´ ˆ
25 A. N. Morin, C. Detrembleur, C. Jerome, P. de Tullio, R. Poli
2 A. Ghadban and L. Albertin, Polymers, 2013, 5, 431–526, p.
496.
3 D. Konkolewicz, Y. Wang, M. Zhong, P. Krys, A. A. Isse,
and A. Debuigne, Macromolecules, 2013, 46, 4303–4312.
26 G. Moad, E. Rizzardo and S. H. Thang, Aust. J. Chem., 2005,
58, 379–410.
A. Gennaro and K. Matyjaszewski, Macromolecules, 2013, 27 G. Paradossi, F. Cavalieri, E. Chiessi, C. Spagnoli and
46, 8749–8772.
M. Cowman, J. Mater. Sci.: Mater. Med., 2003, 14, 687–691.
4 C.-H. Peng, T.-Y. Yang, Y. Zhao and X. Fu, Org. Biomol. Chem., 28 M. Destarac, Polym. Rev., 2011, 51, 163–187.
2014, 12, 8580–8587.
29 G. Moad, E. Rizzardo and S. H. Thang, Aust. J. Chem., 2012,
65, 985–1076.
30 C. Boyer, V. Bulmus, T. P. Davis, V. Ladmiral, J. Q. Liu and
S. Perrier, Chem. Rev., 2009, 109, 5402–5436.
5 W. Wang, J. Zhao, N. Zhou, J. Zhu, W. Zhang, X. Pan,
Z. Zhang and X. Zhu, Polym. Chem., 2014, 5, 3533–3546.
6 J. P. Mendes, F. Branco, C. M. R. Abreu, P. V. Mendonca,
A. V. Popov, T. Guliashvili, A. C. Serra and J. F. J. Coelho,
ACS Macro Lett., 2014, 3, 544–547.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 91225–91234 | 91233

View Article Online
RSC Advances
Paper
31 P. E. Duls, G. David, B. Boutevin, G. Woodward, G. Otter, 48 V. K. Patel, N. K. Vishwakarma, A. K. Mishra, C. S. Biswas,
`
A. Guinaudeau, S. Mazieres and M. Destarac, J. Polym. Sci.,
P. Maiti and B. Ray, J. Appl. Polym. Sci., 2013, 127, 4305–4317.
49 X. Sun, H. Zhang, X. Huang, X. Wang and Q.-F. Zhou,
Polymer, 2005, 46, 5251–5257.
Part A: Polym. Chem., 2012, 50, 1997–2007.
32 M. H. Stenzel, L. Cummins, G. E. Roberts, T. P. Davis,
P. Vana and C. Barner-Kowollik, Macromol. Chem. Phys., 50 N. Rocha, P. V. Mendonca, J. P. Mendes, P. N. Simoes,
2003, 204, 1160–1168.
33 R. W. Simms, T. P. Davis and M. F. Cunningham, Macromol.
Rapid Commun., 2005, 26, 592–596.
34 A. Theis, T. P. Davis, M. H. Stenzel and C. Barner-Kowollik,
Polymer, 2006, 47, 999–1010.
35 J. Schmitt, N. Blanchard and J. Poly, Polym. Chem., 2011, 2,
2231–2238.
A. V. Popov, T. Guliashvili, A. C. Serra and J. F. J. Coelho,
Macromol. Chem. Phys., 2013, 214, 76–84.
51 M. Destarac, C. Brochon, J.-M. Catala, A. Wilczewska and
S. Z. Zard, Macromol. Chem. Phys., 2002, 203, 2281–2289.
52 H. Mori, E. Kudo, Y. Saito, A. Onuma and M. Morishima,
Macromolecules, 2010, 43, 7021–7032.
53 E. L. Eliel, Top. Curr. Chem., 1982, 105, 1–76.
36 E. Girard, T. Tassaing, J.-D. Marty and M. Destarac, Polym. 54 S. Fujita, Tetrahedron, 2006, 62, 691–705.
Chem., 2011, 2, 2222–2230. 55 R. Bentley, Chem. Educ., 2007, 12, 316–321.
37 V. K. Patel, N. K. Vishwakarma, A. K. Mishra, C. S. Biswas and 56 D. Britton, F. Heatley and P. A. Lovell, Macromolecules, 1998,
B. Ray, J. Appl. Polym. Sci., 2012, 125, 2946–2955. 31, 2828–2837.
38 D. Charmot, P. Corpart, H. Adam, S. Z. Zard, T. Biadatti and 57 J. Bernard, A. Favier, L. Zhang, A. Nilasaroya, T. P. Davis,
G. Bouhadir, Macromol. Symp., 2000, 150, 23–32.
39 D. J. Keddie, C. Guerrero-Sanchez, G. Moad, R. J. Mulder,
C. Barner-Kowollik and M. H. Stenzel, Macromolecules,
2005, 38, 5475–5484.
E. Rizzardo and S. H. Thang, Macromolecules, 2012, 45, 58 A. Favier, C. Barner-Kowollik, T. P. Davis and M. H. Stenzel,
4205–4215. Macromol. Chem. Phys., 2004, 205, 925–936.
40 M. Destarac, D. Charmot, X. Franck and S. Z. Zard, 59 G. Pound, J. B. McLeary, J. M. McKenzie, R. F. M. Lange and
Macromol. Rapid Commun., 2000, 21, 1035–1039.
41 D. J. Keddie, Chem. Soc. Rev., 2014, 43, 496–505.
42 D. Fournier, R. Hoogenboom and U. S. Schubert, Chem. Soc.
Rev., 2007, 36, 1369–1380.
B. Klumperman, Macromolecules, 2006, 39, 7796–7797.
60 Y. Yan, W. Zhang, Y. Qiu, Z. Zhang, J. Zhu, Z. Cheng,
W. Zhang and X. Zhu, J. Polym. Sci., Part A: Polym. Chem.,
2010, 48, 5206–5214.
43 M. Benaglia, J. Chiefari, Y. K. Chong, G. Moad, E. Rizzardo 61 R. Fleet, J. B. McLeary, V. Grumel, W. G. Weber, H. Matahwa
and S. H. Thang, J. Am. Chem. Soc., 2009, 131, 6914–6915. and R. D. Sanderson, Macromol. Symp., 2007, 255, 8–19.
44 A. Gregory and M. H. Stenzel, Prog. Polym. Sci., 2012, 37, 38– 62 K. Skrabania, A. Miasnikova, A. M. Bivigou-Koumba,
105.
D. Zehm and A. Laschewsky, Polym. Chem., 2011, 2, 2074–
45 D. Quemener, T. P. Davis, C. Barner-Kowollik and
M. H. Stenzel, Chem. Commun., 2006, 5051–5053.
46 H. C. Kolb, M. G. Finn and K. B. Sharpless, Angew. Chem., Int.
Ed., 2001, 40, 2004–2021.
2083.
63 H. Willcock and R. K. O'Reilly, Polym. Chem., 2010, 1, 149–
157.
64 D. J. Keddie, G. Moad, E. Rizzardo and S. H. Thang,
Macromolecules, 2012, 45, 5321–5342.
´
47 D. Quemener, M. L. Hellaye, C. Bissett, T. P. Davis, C. Barner-
Kowollik and M. H. Stenzel, J. Polym. Sci., Part A: Polym. 65 C. Barner-Kowollik, F. E. Du Prez, P. Espeel, C. J. Hawker,
Chem., 2008, 46, 155–173.
T. Junkers, H. Schlaad and W. van Camp, Angew. Chem.,
Int. Ed., 2011, 50, 60–62.
91234 | RSC Adv., 2015, 5, 91225–91234
This journal is © The Royal Society of Chemistry 2015