Block copolymerization of vinyl acetate and vinyl neo -decanoate mediated by dithionodisulfide

Article abstract of DOI:10.1021/ma1000139

Block copolymerization of vinyl acetate (VAc) and vinyl neo-decanoate (VNDc) is carried out in the presence of a disulfide, isopropylxanthic disulfide (DIP), using 2,2′-azoisobutyronitrile (AIBN) as the radical initiator. The polymerization proceeds in a controlled/'living' style, as illustrated by stepwise increase in molecular weight and relatively narrow molecular weight distribution of the final product. The reaction mechanism is investigated in detail for the system of VAc homopolymerization in the presence of DIP. The results of chromatography, NMR, and mass spectra reveal that there exists two kinds of RAFT agents, that is, S-(cyano)isopropyl O-isopropyl xanthate and diisopropyl dithiocarbonate, the former coming from the reaction of 2-cyano-isopropyl radical with DIP and the latter being formed in situ during a series of radical process participated by the monomer. High efficiency of the cross initiation is achieved for the sequential polymerization. The block lengths are well controlled by the ratio of monomer to RAFT agents. The resulting block copolymer, PVAc-b-PVNDc, is hydrolyzed to prepare PVOH-b-PVNDc. These block copolymers, before and after hydrolysis, undergo self-assembly in solution and phase separation in bulk state.

Full text of DOI:10.1021/ma1000139

4500 Macromolecules 2010, 43, 4500–4510
DOI: 10.1021/ma1000139
Block Copolymerization of Vinyl Acetate and Vinyl neo-Decanoate
Mediated by Dithionodisulfide
Yuankai Gu, Junpo He,* Changxi Li, Changming Zhou, Shijie Song, and Yuliang Yang
Department of Macromolecular Science, Fudan University, Shanghai, 200433, and the Key Laboratory of
Molecular Engineering of Polymers, Ministry of Education, China
Received January 4, 2010; Revised Manuscript Received April 16, 2010
ABSTRACT: Block copolymerization of vinyl acetate (VAc) and vinyl neo-decanoate (VNDc) is carried out
in the presence of a disulfide, isopropylxanthic disulfide (DIP), using 2,20-azoisobutyronitrile (AIBN) as the
radical initiator. The polymerization proceeds in a controlled/“living” style, as illustrated by stepwise increase
in molecular weight and relatively narrow molecular weight distribution of the final product. The reaction
mechanism is investigated in detail for the system of VAc homopolymerization in the presence of DIP. The
results of chromatography, NMR, and mass spectra reveal that there exists two kinds of RAFT agents, that
is, S-(cyano)isopropyl O-isopropyl xanthate and diisopropyl dithiocarbonate, the former coming from the
reaction of 2-cyano-isopropyl radical with DIP and the latter being formed in situ during a series of radical
process participated by the monomer. High efficiency of the cross initiation is achieved for the sequential
polymerization. The block lengths are well controlled by the ratio of monomer to RAFT agents. The resulting
block copolymer, PVAc-b-PVNDc, is hydrolyzed to prepare PVOH-b-PVNDc. These block copolymers,
before and after hydrolysis, undergo self-assembly in solution and phase separation in bulk state.
Introduction
however, that DIP is rather a precursor of RAFT agent than an
iniferter during the polymerization of vinyl alkanoates, thereby
Controlled/“living” radical polymerizations based on the
RAFT (reversible addition-fragmentation chain transfer) pro-
cess have been extensively studied in the past 10 years.1,2 The
living feature of the RAFT-based polymerization is achieved
through the reversible chain transfer of propagating radicals
toward thiocarbonylthio compounds such as dithioesters and
trithiocarbonates.2 When xanthates are used as chain transfer
agent, the reaction is independently nominated as macromolecular
design via the interchange of xanthates (MADIX) processes,3-5
which is a very efficient approach in the synthesis of narrow
disperse vinyl alkanoate polymers.6-13 Usually, the studies of the
RAFT and MADIX polymerizations require the synthesis of
thiocarbonylthio compounds on a laboratory scale. The synthesis
of dithioesters and xanthates is generally done using Grignard
reagent,1 whereas the latter can also be synthesized from corre-
sponding salts.5 Some of these compounds are already commer-
cially available.14,15 An alternative way is to form RAFT agent in
situ by the reaction of radical initiator and disulfide. Sanderson
and coworkers have reported RAFT polymerization initiated by
AIBN in the presence of bis(dithiobenzoyl) disulfide,16 in which
dithioester derived from fragments of AIBN and disulfide17,18
seems to play the role of RAFT agent. Nevertheless, the reports on
the in situ formation of dithioesters or xanthates are quite seldom
up to date.19,20
resulting in narrower disperse polymer products.
VNDc is a functional monomer with bulky branched alkyl
group (Scheme 1). It is usually used to copolymerize with VAc to
endow the product with higher water and alkaline resistance due
to the hydrophobicity of VNDc units.25,26 VNDc has also been
homopolymerized through MADIX process.9,27 Nevertheless,
the synthesis of block copolymer of VNDc and VAc has never
been reported. In addition, the block copolymer prepared in the
present work has been selectively hydrolyzed on PVAc segments,
taking advantage of alkaline resistance of VNDc units.28,29
Amphiphilic diblock copolymer possessing semicrystalline poly-
(vinyl alcohol) segments, PVOH-b-PVNDc, is therefore obtained.
Experimental Section
Materials. DIP (XiaWei, g98%) was recrystallized from ethanol.
VAc (Sinopharm Chemicals, g99%) and VNDc (Helixon
Chemicals, g99%) were distilled after being stirred over CaH2
for 24 h. Benzene (ShenXiang Chemicals, g99%) and tetrahydro-
furan (Sinopharm, 99%) were refluxed over sodium and distilled.
2,2-Azobis-(isobutyronitrile) (AIBN, Shanghai fourth Factory of
Chemicals, 99%) was recrystallized from methanol. Methanol
(99.5%), dimethylsulfoxide (99%) (both LingFeng Chemicals),
petroleum ether (ShenXiang Chemicals, 99%), acetone (Dahe
Chemicals, g99.5%), and N-methyl-2-pyrrolidone (Sinopharm
Chemicals, g98%) were used as received.
In the present work, we use isopropylxanthic disulfide (DIP,
Scheme 1), a conventional rubber vulcanization accelerator, to
mediate the RAFT/MADIX polymerization of vinyl acetate (VAc)
and vinyl neo-decanoate (VNDc). DIP is a bifunctional xantho-
genic derivative and has been reported as a photo or thermal
iniferter in radical polymerizations of styrene, (meth)acrylates,
acrylonitrile, and VAc.21-24 The present work demonstrates,
Measurements. 1H and 13C NMR and HSQC measurements
were carried out on a Bruker (500 MHz) NMR instrument,
using tetramethylsilane (TMS) as the interior reference. Gel
permeation chromatography (GPC) was performed on a Waters
410 system equipped with three TSK columns (TSK Gel H-type,
˚
pore size 15, 30, and 200 A) in series, a Waters 410 RI detector,
and a Waters 486 UV detector (300 and 254 nm), using THF as
the eluent at a flow rate of 1 mL/min at 40 °C. The columns were
calibrated by narrow polystyrene standard with molecular
*Corresponding author. Fax: þ86-21-6564-0293. E-mail: jphe@
fudan.edu.cn.
pubs.acs.org/Macromolecules
Published on Web 04/27/2010
r 2010 American Chemical Society

Article
Scheme 1. Chemical Structure of DIP and Monomer VNDc
Macromolecules, Vol. 43, No. 10, 2010 4501
the reaction mixture was taken from the flask at predetermined
periods and analyzed by GPC. The final product was obtained
after three times of dissolving in THF and precipitating from
cool petroleum ether (bp 60-90 °C). Mn,GPC = 22 000 g/mol
(24 h), PDI = 1.48.
For the isolation of small molecular species formed during
induction period (P254 and P300, see the Results and Discussion),
the reaction was stopped after heating the polymerization
mixture for 8 h. Solvent and monomer were removed by rotary
evaporation. The residual viscous mixture was subsequently
fractionated by column chromatography, employing gradient
eluent of chloroform/hexane (from 1/1 to 9/1 v/v). The purifica-
tion of each fraction was repeated three times by column
chromatography. The obtained liquid substances were analyzed
weight ranging from 2.2 ꢀ 103 to 5.2 ꢀ 105 g/mol. High-
performance liquid chromatography (HPLC) was performed
on an instrument composed of a Waters 515 pump, a C-18
column, and a UV detector with the wavelength set at 254 and
300 nm. Acetonitrile/water (v/v 85/15) was used as eluent
(1.0 mL/min) at 40 °C. For VAc polymerization, monomer
conversion was measured by TGA performed on a Perkin-Elmer
Pyris 1 instrument under a nitrogen atmosphere (40 mL/min). The
temperature was elevated from 20 to 700 °C at a rate of 20 °C/min.
The solvent and monomer evaporated rapidly up to 150 °C,
whereas polymer degradation starts at 300 °C. Polymer content
was calculated using weight loss above 300 °C.
Gas chromatography-mass spectrometry (GC-MS) was per-
formed on a Thermo Focus DSQ system, equipped with a mass-
selective detector using electron impact ionization. Analytes
were separated by an HP-5MS capillary column of 30 m (0.25
i.d. and 0.25 μm film thickness), which was inserted directly into
the ion source of the MS system. Helium (99.999%) was the
carrier gas maintained at a flow-rate of 1 mL/min. The injector
was kept at 250 °C, and samples were split injected (1 μL, split
ratio 30:1). The column oven temperature was programmed to
start at 60 °C for 2 min, ramp at 20 °C/min for 12 min, and held
at 300 °C for 5 min. EI spectra were scanned between 41 and 350
Da in the full-scan acquisition mode. The transferline and EI
source temperature were both 250 °C. The electron multiplier
voltage was set on 70 eV.
Matrix-assisted laser desorption ionization-time-of-flight
mass spectroscopy (MALDI-TOF MS) measurements were
performed using a Voyager DE-STR instrument (Applied
Biosystems) equipped with a 337 nm nitrogen laser. Data were
acquired in the reflector mode. Sodium trifluoroacetate and
2,5-dihydroxybenzoic acid (DHB) were used as the cationiza-
tion agent (10 mg/mL in THF) and the matrix (20 mg/mL in
THF), respectively. The polymer sample was dissolved in THF
at a concentration of 10 mg/mL. The matrix, cationization
agent, and sample solutions were premixed at a 10:1:2 (v/v)
ratio. Approximately 0.5 μL of the obtained mixture was
dropped on the target plate. After the solvent was evaporated,
the target was inserted into the mass spectrometer. For each
spectrum, 1000 laser shots were accumulated.
1
by NMR and GC-MS. P300: H NMR: δ 1.37 (6H, d, SCH-
(CH3)2), 1.39 (6H, d, OCH(CH3)2), 3.75-3.83 (1H, m, SCH-
(CH3)2), 5.75-5.83 (1H, m, OCH(CH3)2). 13C NMR: δ 21.3
(SCH(CH3)2), 22.3 (OCH(CH3)2), 29.7 (SCH(CH3)2), 40.5
(OCH(CH3)2), 213.8 (CdS). GC (Figure 6): 100%, MS (70 eV) m/
z: 178 [Mþ], 136 [C4H8S2Oþ], 120 [C4H8S2þ], 103 [C4H7SOþ], 94
[CH2S2Oþ], 75 [C3H7Sþ], 59 [C3H7Oþ], 43 [C3H7þ]. P254
:
1H NMR: δ 2.15 (3H, s, OdCCH3), 3.72-3.76 and 4.08-4.13
(1H, q, SCH2CH), 6.63-6.66 (1H, q, SCH(CH2)O). 13C NMR: δ
20.8 (OdCCH3), 41.0 (SCH2CH), 81.0 (SCH(CH2)O), 169.6
(CH3CdO), 195.1 (S;CdO). GC (Figure 8): 96.3%, MS
(70 eV) m/z: 179 [M-Hþ], 118 [C4H6SO2þ], 90 [C2H2S2þ], 76
[C2H4SOþ], 59 [C2H3O2þ], 43 [C2H3Oþ].
The polymerization of VNDc was carried out using the
same procedure as that in VAc system, with feeds of monomer
(28.40 g, 0.14 mol), DIP (0.20 g, 0.74 mmol), and AIBN (0.12 g,
0.73 mmol) in 32 mL of benzene. The final product was obtained
after three times of dissolving in THF and precipitating from
methanol. Mn,GPC = 21 900 g/mol (30 h), PDI = 1.48.
A model reaction between AIBN (1.02 g, 6.22 mmol) and DIP
(1.55 g, 5.74 mmol) was carried out in benzene (50 mL) in the
absence of monomer. The solution was deaerated through three
cycles of freezing-pumping-thawing and warmed to 60 °C
under argon for 20 h. The resulting reaction product was
analyzed by GC-MS.
Synthesis of PVAc-b-PVNDc Block Copolymers. The synth-
esis of the first block, PVAc, is carried out using same process as
that in the above kinetic study except the feeding amount: VAc
(30.50 g, 0.35 mol), DIP (0.50 g, 1.85 mmol), and AIBN (0.30 g,
1.83 mmol) in benzene (22 mL). The reaction mixture was
heated for 16 h. A viscose liquid was obtained after three times
of dissolving in THF and precipitating from cool petroleum
ether. The viscose liquid became solid after being dried in
vacuum at room temperature for 3 days. The solid was redis-
solved in acetone and dialyzed for 3 days to eliminate the small
molecular impurities completely. The final product was PVAc
with xanthate terminus. Conversion = 32%, Mn,GPC = 5600
g/mol, PDI = 1.35. Mn,NMR = 9600 g/mol (in acetone-d6).
VNDc (19.36 g, 0.10 mol), PVAc with xanthate terminus
(Mn,NMR = 9600 g/mol) (3.00 g, 0.32 mmol), and AIBN (0.04 g,
0.24 mmol) were dissolved in benzene (20 mL) in a 100 mL flask.
The solution was deaerated through three cycles of freezing-
pumping-thawing. The reaction mixture was warmed to 60 °C
under argon. For kinetic study, an aliquot of the reaction mixture
was taken out from the flask at predetermined periods and
analyzed by GPC.
Dynamic light scattering (DLS) was performed on a modified
commercial light scattering spectrometer (ALV/SP-125) equipped
with an ALV-5000 multidigital time correlator and ADLAS
DPY425II solid-state laser (output power = 22 mW at λ0 =
632.8 nm, angle = 90°). The scattering cell was surrounded by a
bath of filtered toluene at a temperature of 298.13 K. Thermal
properties of block copolymers were determined by a Mettler
DSC-1 apparatus using indium (Tm = 156.60 °C and ΔHf0
=
28.45 J/g) as standard and nitrogen as flow gas. The samples were
heated to 300 °C (20 °C/min), kept for 5 min, cooled to -20 °C
(20 °C/min), and then heated to 300 °C at a rate of 20 °C/min. For
the annealing, the sample was heated to 200 °C (10 °C/min), kept
for 90 min, cooled to -40 °C (10 °C/min), and then heated to
300 °C at a rate of 10 °C/min. IR spectra were obtained on a
Magna-550 FTIR instrument.
To obtain block copolymer, the reaction was conducted using
the same mixture for a period of 24 h, followed by three times of
dissolving in THF and precipitating from methanol/water (v/v
1:1), and dried in vacuum for 1 week at 50 °C. Conversion =
12%, Mn,GPC = 12 200 g/mol, PDI = 1.36. Mn,NMR = 13 200
g/mol (in THF-d8).
Hydrolysis of PVAc-b-PVNDc Block Copolymers. A solution
of PVAc(11200)-b-PVNDc(38300) (0.70 g) in 5 mL of THF was
mixed with a solution of potassium carbonate (1.20 g) in 40 mL
of methanol. The mixture was stirred at 50 °C for 15 h. After the
Kinetic Study of RAFT Homopolymerizations of VAc and
VNDc Mediated by DIP. VAc (31.70 g, 0.37 mol), DIP (0.50 g,
1.85 mmol), and AIBN (0.45 g, 2.74 mmol) were dissolved in
benzene (22 mL) in a 100 mL flask. The solution was deaerated
through three cycles of freezing-pumping-thawing. The reac-
tion mixture was warmed to 60 °C under argon. An aliquot of

4502 Macromolecules, Vol. 43, No. 10, 2010
Gu et al.
Scheme 2. Outline of the Synthetic Route
Figure 1. Evolution of molecular weight with increasing conversion in
(a) VAc and (b) VNDc solution polymerization mediated by DIP.
gives inverse peaks and partially overlaps with unknown
species (inset in Figure 1a); therefore, monomer conversion is
measured by TGA. The polydispersity is close to 1.5, the
lowest theoretical value of radical polymerization, although
larger than that of typical living polymerization due to the
quasi-living feature of MADIX system.
An induction period of up to 5 h is observed for both
systems, as shown in Figure 2. At the end of the induction
period, molecular weight starts to increase linearly with mono-
mer conversion. Nevertheless, the molecular weight increases
abruptly when it starts to grow, as shown in Figure 2b,
exhibiting a “hybrid” behavior of conventional and controlled
radical polymerization in the initial stage. In the system of
VNDc, the deviation of molecular weight from a linear depen-
dence on monomer conversion is more obvious in which the
extrapolation does not pass the origin of the coordinates
(dashed line in Figure 2d). This is in sharp contrast with the
polymerization behavior of styrene in the presence of dithio-
esters, in which a stepwise increase in molecular weight
is observed from the start of the polymerization.31,32 The
“hybrid” behavior has been observed in RAFT polymerization
of MMA and VAc mediated by either xanthates7 or
dithioester33 and has been ascribed to larger propagation rate
in relative to the rate of RAFT process.
GPC is used to monitor the reaction in the induction period,
setting UV detector at double wavelengths, 254 and 300 nm,
which are close to the two peak absorptions in UV spectrum of
DIP. Figure 3 shows the elution diagram of VAc polymeriza-
tion mixture at various reaction times in the initial stage. For
both working wavelengths a new peak appears at the right side
of DIP, thereafter denoted as peaks P254 and P300, respectively.
As the reaction proceeds, the intensity of DIP peak decreases as
those of P254 and P300 increase. After complete consumption of
DIP, the intensity of P254 stays constant, whereas that of P300
decreases when the polymer peak appears (insets in Figure 3),
indicating participation of P300 species in the polymerization.
However, remarkable amount of P300 remains unreacted up to
high conversion of monomer, as shown by GPC trace for 24 h
in the inset in Figure 3b.
removal of methanol by distillation, the reaction mixture was
dispersed in water and transferred to a dialysis package. After
dialysis for 4 days in water, the aqueous solution was lyophilized
for 2 days to get a cotton-like copolymer. GPC analysis was not
done because of poor solubility of the hydrolyzed product in
THF. Yield = 65.6%.
Hydrolysis of both homopolymers was conducted under
otherwise identical conditions except for the reaction time. In
the case of PVNDc, no reaction occurred after 24 h, whereas a
period of 2 h is enough for completely hydrolysis of PVAc.
Self-Assembly of the Diblock Copolymers. In typical, a sample
of block copolymer, PVAc(11200)-b-PVNDc (10200) (60 mg,
2.6 ꢀ 10-3 mmol) in 10 mL acetone was stirred overnight. The
dispersion (6 mg/mL) was filtered by passing through a PTFE
syringe filter (pore size 0.45 μm) before being analyzed by DLS.
Results and Discussion
RAFT Polymerizations of VAc and VNDc Mediated by
DIP. The general synthetic route is outlined in Scheme 2. As
the first step, we study the homopolymerizations of VAc and
VNDc, both of which are carried out in benzene solution at
60 °C, using AIBN as the initiator and DIP as the MADIX
agent precursor. It is reported that a trace amount of impurity
in chain transfer agents such as xanthate8 and dithioesters30
would cause inhibition and retardation. The compound DIP,
with a purity of >98% as received, has been recrystallized to
reach a purity of as high as 99.4% (by HPLC). As the
polymerization proceeds, the reaction solution becomes more
and more viscous. An aliquot of the reaction mixture is taken at
a predetermined period and analyzed directly by GPC
equipped with a set of special columns capable of resolving
both polymeric and small molecular species.31 Therefore, the
molecular weight of the product and the monomer conversion
are obtained simultaneously.
The peaks of P254 and P300 may be ascribed to possible
xanthate species formed in the reaction of DIP- and AIBN-
derived radical. It has been reported that bis(dithiobenzoyl)
disulfide,16 in reaction with AIBN, formed dithioester, which
acted in situ as a RAFT agent. However, the resulting dithio-
ester has not been identified in ref 16. In the present work,
species of P254 and P300 are isolated by column chromatogra-
phy using the reaction mixtures in the induction period, that is,
before the beginning of polymerization.
Figure 1 displays the GPC traces monitoring the RAFT
homopolymerizations of VAc and VNDc mediated by DIP.
There is a clear shift of Mn to larger molecular weight along
with a decrease in monomer peak intensities. Note that VAc
Figure 4 shows an HPLC diagram in which species of P254
and P300 are observed at elution time of 3.2 and 6.0 min,
respectively, as detected under 254 and 300 nm. The correlation

Article
Macromolecules, Vol. 43, No. 10, 2010 4503
Figure 2. (a,c) Reaction kinetics and (b,d) the increase in molecular weight along with monomer conversion during homopolymerizations of VAc and
VNDc in the presence of DIP. Feeding molar ratio: VAc/DIP/AIBN 200/1/1.5; VNDc/DIP/AIBN 200/1/1. The molecular weights are reported in
relative to polystyrene standards.
Figure 3. GPC diagrams detected at (a) 254 and (b) 300 nm for solution
polymerization of VAc initiated with AIBN and mediated by DIP at
60 °C. Feed: VAc/DIP/AIBN 200/1/1.5 (molar ratio).
Figure 4. HPLC diagrams of reaction mixture of VAc, AIBN, and DIP
at 60 °C in benzene during the induction period. Feed: VAc/DIP/AIBN
200/1/1.5 (molar ratio). The elution is detected under (a) 254 and
(b) 300 nm.
between GPC and HPLC results is done using the authentic
samples isolated by column chromatography employing gra-
dient eluent of chloroform/hexane (from 1/1 to 9/1 v/v). It is
obvious that P254 and P300 are different fractions in the HPLC
profile, although they are very close in GPC diagram. These
species are characterized in the following section. A small peak,
partially overlapped with benzene signal, appears at elution
time of 4.2 min in Figure 4b (S300) and turns out to be
S-(cyano)isopropyl xanthate (3 in Scheme 3) (Supporting
Information). Compound 3 is generated by the reaction of
2-cyano-isopropyl radical and DIP. In addition, broad multi-
modal peaks appear in the range of 6.0 to 7.3 min under both
wavelengths, of which the analytical data is unavailable
because of low content and difficulty in separation.
Scheme 3. Reaction Mechanism between AIBN and DIP in the
Presence of Vinyl Acetate
The isolated species of P254 and P300 are analyzed by NMR
and GC-MS. As shown in Figure 5, a xanthate structure,
diisopropyl dithiocarbonate, is assignable from both 1H and
13C NMR spectra of P300. In the 1H spectrum, four groups of
protons are observed at chemical shift of 5.78, 3.79, 1.39, and

4504 Macromolecules, Vol. 43, No. 10, 2010
Gu et al.
Figure 5. 1H NMR and 13C NMR spectra of P300 (diisopropyl dithiocarbonate) in CDCl3.
Figure 6. GC-MS (EI) spectra of species P300 (diisopropyl dithiocarbonate).
1.37 ppm, which are assigned to methines and methyls of
isopropyloxy and isopropylthio groups, respectively. In
addition, the integration and the splitting constants correlate
very well with the proposed structure. GC shows a single
peak at retention time of 6.63 min (Figure 6a); the EI-MS is
given in Figure 6b. The molecular ion at m/z = 178 agrees
with the formula mass of isopropyl xanthate; the base peak is
the isopropyl cation (m/z = 43). Proposed complete frag-
mentation schemes for fractions of P254 and P300 are given in
the Supporting Information.
xanthate according to the work by Zard17 and Thang.18
Sanderson and coworkers performed RAFT polymerization
initiated by AIBN in the presence of bis(dithiobenzoyl)
disulfide.16 They observed that dithioester derived from frag-
ment of AIBN and disulfide had formed in situ in the reaction
system. Beckman and coworkers prepared xanthate with
functional groups from the reaction of azo compound and
O,O-diethyl bisxanthate.34 In the present work, a model reac-
tion between AIBN and DIP in the absence of monomer indeed
gives similar results as those in refs 16-20. GC-MS spectrum
shows high content of S-(cyano)isopropyl xanthate (RT =
8.13 min with m/z = 203) in the reaction mixture (Sup-
porting Information).
We propose that the formation of diisopropyl dithiocar-
bonate and the cyclic 1,3-dithiol-2-one compound is through
a series of radical processes, as shown in Scheme 3. The
process is triggered by 2-cyano-isopropyl radical, 1, derived
from AIBN. The attack of 1 to DIP results in the formation of
2, a thio-centered radical, and a xanthate 3. The thio-centered
radical can either recouple to 1 to give 3 or, more possibly,
add to monomer to give 4 as normal initiation. However,
there is no further chain growth because 4 tends to cyclize
through an intromolecular radical transfer process, yielding 6
(P254) and releasing an isopropyl radical. The isopropyl
radical can either recombine with 2 to form diisopropyl
xanthate 8 (P300) or react with DIP to result in 2 and 8. The
overall consequence of the process is the formation of 3, 6,
and 8 by the consumption of AIBN, DIP, and monomer. The
cyclic compound 6 will not take part in further reaction,
reaching a stationary concentration after the radical process,
as described above. Xanthates 3 and 8 will act as RAFT
agents in the subsequent polymerization.
Figure 7 shows the 1H and 13C NMR and HSQC spectra of
P254. In the former, the signal at chemical shift of 2.15 ppm
comes from acetoxy group, and those at 6.65, 4.10, and 3.75
ppm are assignable to cyclic -CH-CH2- system in which
the geminal splitting of methylene is -12.95 Hz. 13C NMR
shows carbonyl group at 195 ppm in addition to that at 170
ppm for carbonyl in acetoxy. These lead to the assignment of
a cyclic 1,3-dithiol-2-one structure. The integration and the
2D NMR, HSQC, and the splitting constants correlate very
well with the proposed structure. GC shows two peaks, the
smaller one at 5.27 min is residual AIBN, and the main peak
at 8.57 min gives the mass spectrum shown in Figure 8b. The
molecular ion is not observed at m/z = 178, possibly because
of the instability of the cyclic structure. A small peak appears
at m/z = 179, which is assigned to protonated molecules of
the cyclic compound. The base peak at m/z = 43 is acetyl
cation.
Therefore, it seems that in the polymerization of VAc, the
main products formed during the induction time are diiso-
propyl dithiocarbonate and the cyclic 1,3-dithiol-2-one com-
pound. These are quite unexpected because the anticipated
product in the reaction of AIBN and DIP is S-(cyano)isopropyl

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Macromolecules, Vol. 43, No. 10, 2010 4505
Figure 7. (a) 1H NMR, (b) 13C NMR, and (c) HSQC spectra of P254 in CDCl3.
Figure 8. GC-MS spectra of P254. (a) GC and (b) EI-MS.
The above mechanism is very similar to that proposed by
Gareau et al.35 In their work, they prepared unsaturated
cyclic 1,3-dithiol-2-ones from the reaction between alkynes
and DIP. However, they observed that most of alkenes were
unreactive and do not yield cyclic 1,3-dithiol-2-ones. Instead,
some vinyl compounds gave double-addition products of
disulfide toward the vinyl group. We indeed do not observe
any peaks analogous to P254 and P300 in the reaction of DIP
with AIBN in the presence of other vinyl monomer such as
styrene or methyl methacrylate. Therefore, the formation of
6 and 8 is quite specific for the monomer of VAc.
product purified by dialysis and freeze-drying. For PVAc
(A), the methine and methylene protons of the main chain
show broad complex signals at 4.82-5.05 and 1.72-1.93
ppm, respectively, resulting from stereoisomers, with inte-
gration ratio of 1:2. The acetoxy appears as three peaks due
to different configuration sequences of the triad, mm, mr,
and rr. The methine of O-isopropyl end group shows a weak
but clear heptet around 5.75 ppm. The heptet seems to be
further split or overlapped with another heptet, which
cannot be currently explained. Theoretically, there are three
kinds of methyl termini derived from isopropyl radical,
2-cyano-isopropyl radical (both at R-end) and O-isopropyl
fragment of xanthate (ω-end), respectively. Unfortunately, it
is difficult to assign these methyl signals in the range of
The end-group analysis by NMR and MALDI-TOF MS
may provide more information about the reaction mechan-
ism. Figure 9 shows the H NMR of the polymerization
1

4506 Macromolecules, Vol. 43, No. 10, 2010
Gu et al.
Figure 10. Matrix-assisted laser desorption ionization time-of-flight
mass spectrum of PVAc with xanthate terminus (Mn,GPC = 2100 g/mol,
Mn,NMR = 2400 g/mol); matrix: DHB; cationization agent: sodium
trifluoroacetate.
Figure 9. 1HNMR spectra of (A) PVAc with xanthate terminus
(Mn,NMR = 9600 g/mol, PDI = 1.35) in acetone-d6 and (B) PVNDc
with xanthate terminus (Mn,NMR = 8500 g/mol, PDI = 1.45) inTHF-d8.
unit. The main series is assignable to polymer chains
with R-cyanoisopropyl and ω-xanthate termini, which
results from 3 and new initiation of AIBN. Polymer with
R-isopropyl and ω-xanthate termini, derived from 8, shows a
signal at 1663.9 with relatively low intensity. In addition,
some terminated species are observed at m/z = 1641.0,
1658.0, and 1683.0, which are assigned to H-terminated
chains (by disproportionation), recombination terminated
chains with R- and ω-isopropyl termini, and recombination
terminated chains with R-cyanoisopropyl and ω-isopropyl
termini, respectively. The origins of these species are quite
complex. Whereas chains with unsaturated terminus, the
counterparts of H-terminated ones in disproportionation,
are observed at m/z = 1639.0, these species, saturated and
unsaturated, can also be formed by disproportionation
between propagating chains and primary radicals such as
isopropyl and 2-cyano-isopropyl radicals. In a similar way,
recombination termination may occur between homologous
propagating chains or between propagating chain and pri-
mary radicals. The former pathway would result in the
formation of telechelic species with cyanoisopropyl termini.
However, these species are not observed in the spectrum.
Therefore, we propose that the recombination terminated
chains form by cross termination between propagating
chains and isopropyl radical, the latter being generated as
the leaving group in the chain transfer process of 8.
0.70 to 1.72 ppm because the signals in this region are quite
complex. Similarly, the methine signal of O-isopropyl termi-
nus in PVNDc appears as a broad complex at ∼5.75 ppm
(Figure 9B). The signal broadening may be due to mediate
solubility of PVNDc in THF. PVNDc is insoluble in most
organic solvents such as acetone, DMF, N-methylpyroli-
done, chloroform, dichloromethane, cyclohexane, toluene,
and benzene and is partially soluble in DMSO at 80 °C. In
fact, THF is the most soluble solvent we have ever found for
homo PVNDc. Therefore, NMR spectroscopy confirms the
presence of xanthate terminus but does not distinguish the
structures of the other end, either isopropyl from 8 or
cyanoisopropyl from 3.
To analyze the structure of end group, MALDI-TOF MS
is carried out on a PVAc sample with low molecular weight,
2400 g/mol (by NMR, Supporting Information). In fact, this
is the lowest molecular weight we have ever obtained because
of the abrupt and uncontrolled polymerization in the initial
stage. According to previous reports,36,37 we have tried the
following substances as the matrix: 2[(2E)-3-(4-tert-butyl-
phenyl-2-methylprop-2-enylidene) malononitrile (DCTB),
2,5-di-hydroxy-benzoic acid (DHB), R-cyano-4-hydroxycin-
namic acid (CHCA), and 3-β-indole acrylic acid (IAA).
DHB gives a clearly better resolved spectrum, as shown in
Figure 10. There are five series of signals, all of which show
an interval of 86 mass units corresponding to VAc repeating
From the results of chromatography, NMR, and MALDI-
TOF MS, it is clear that the reaction of AIBN, DIP, and VAc
results in the formation of 3, 6, and 8 in the induction period,

Article
Macromolecules, Vol. 43, No. 10, 2010 4507
Figure 11. GPC diagrams of samples taken at various conversions
(indicated in the Figure) in VNDc polymerization mediated by PVAc
with xanthate terminus (9600 g/mol).
Figure 12. 1HNMR spectrum of PVAc(11200)-b-PVNDc(38300) in
THF-d8.
whereas 3 and 8 mediate further RAFT polymerization of
VAc. Although 8 is a main product, as indicated by chroma-
tography, chain species derived from 8 constitute only a minor
fraction of the polymer products. Instead, the major part of
living chains is initiated by 2-cyano-isopropyl radical, either from
3 or from continuous initiation of AIBN. This may be a con-
sequence of poor leaving and reinitiating abilities of isopropyl in
relative to cyanoisopropyl group. Indeed, Klumperman and
coworkers have found that cyanoisopropyl is a better leaving
and reinitiating group than tert-butyl,38 a group similar to
isopropyl, in RAFT polymerization of VAc.
Synthesis and Hydrolysis of Block Copolymers of VAc and
VNDc. After the induction period, the reaction is trans-
formed into a typical MADIX system in which 3 and 8 play
the role of chain transfer agents. A number of block co-
polymers are prepared by chain extension polymerization of
VNDc using the first segment as the macro chain transfer
agent. For the first block, the molecular weight is controlled
by the molar ratio of VAc to DIP, whereas the ratio of DIP to
AIBN determines the polymerization rate and the inhibition
time. The results are listed in Table 1. The molecular weight
measured by GPC is reported in relative to polystyrene
standards, giving lower Mn,GPC in relative to that measured
by NMR, Mn,NMR, which is more close to the real value.
Polydispersity is reasonably low in all cases.
The first block is purified by repeated precipitation in iced
petroleum ether. (For the measurement, the sample is dia-
lyzed in acetone for 3 days and freeze-dried overnight.)
The first block is dissolved in benzene and mixed with a

4508 Macromolecules, Vol. 43, No. 10, 2010
Gu et al.
predetermined amount of AIBN and VNDc. The mixture is
heated to 60 °C to start the block copolymerization. GPC
traces of a typical polymerization, shown in Figure 11,
illustrate a stepwise increase in molecular weight and high
efficiency of the transformation to the second block.
The ratio of repeating units (m/n in the block copolymer) is
measured by 1H NMR using samples dried in vacuum for 1
week at 50 °C after precipitation. As shown in Figure 12, the
methine signals of the main chain (a and c) from different
monomer units overlap in the range of 4.8 to 5.0 ppm. The
percentage of the VNDc units is estimated by the ratio of the
integration, Ac/Aaþc, in which the area of Ac equals to 1/9 of
that of peak e. The results are listed in Table 1.
The pendent ester groups of PVNDc segment are resistant
to alkaline,25-29 whereas those of PVAc segment can easily
be hydrolyzed at room temperature.39 Indeed, we observe
complete hydrolysis of PVAc within 2 h, whereas a homo-
polymer of VNDc remains stable under similar conditions.
Therefore, the block copolymer is selectively hydrolyzed to
prepare an amphiphilic block copolymer, PVOH-b-PVNDc,
which is then purified by dialysis. The final product is
insoluble in organic solvents such as acetone, THF, DMF,
N-methylpyrolidone, chloroform, dichloromethane, cyclo-
hexane, toluene, and benzene and is partially soluble in
DMSO at 80 °C. 1H NMR spectrum is measured in
DMSO-d6, as shown in Figure 13, although not well re-
solved, which is indicative of low solubility or high viscosity
of the solution. The acetoxy signal at 2.0 ppm has disapp-
eared, whereas three singlets appear in the range of 3.95 to
4.50 ppm, which are attributable to pendent hydroxyl group.
The methine signal of VAc units shifts to 3.9 ppm. The
retention of VNDc units after hydrolysis is demonstrated by
the presence of the bulky alkyl protons (e signal in Figure 13).
The presence of both hydroxyl and ester groups in the
hydrolyzed product is further confirmed by IR. (See the
Supporting Information.)
Figure 13. 1H NMR spectrum of hydrolyzed product PVOH(5730)-b-
PVNDc(38300) measured in DMSO-d6 at 80 °C.
Properties of the Block Copolymer. Owing to the hydro-
phobicity of PVNDc segment,27-29 the block copolymer
Figure 14. Size distribution of PVAc-b-PVNDc (with different ratio of repeating units) micelles formed in acetone.
Figure 15. (a) DSC curves of PVAc, PVAc(18000)-b-PVNDc(12200), PVAc(11200)-b-PVNDc (38300), and PVNDc (from top to bottom) and (b)
DSC spectra of PVOH, PVOH(9200)-b-PVNDc(12200), PVAc(5800)-b-PVNDc(38300), and PVNDc (from top to bottom).

Article
Macromolecules, Vol. 43, No. 10, 2010 4509
synthesized in this work displays amphiphilic properties that
would result in self-assembly in selective solvents. However,
the hydrolyzed block copolymer after drying is difficult to be
redissolved or form stable dispersion in many solvents. The
only solvent we have found is DMSO, but the dissolving
should be performed at a temperature higher than 80 °C. We
hereby give only preliminary results on the aggregation of
PVAc-b-PVNDc in solution and bulk state as a demonstra-
tion of successful block copolymer synthesis.
PVAc-b-PVNDc is sonicated and then stirred in acetone, a
selective solvent for PVAc segment. The gel-like polymer
readily forms a more homogeneous dispersion with opale-
scence, which is indicative of micelle formation. The result-
ing dispersion is filtered using a PTFE syringe filter (pore
size: 0.45 μm) before investigation by DLS. As shown in
Figure 14, the hydrodynamic radius (Rh) of the micelles is 44
and 27 nm, respectively, for PVAc(18000)-b-PVNDc(12200)
and PVAc(11200)-b-PVNDc(10200) with narrow distribu-
tions. These values are smaller than the chain lengths of the
block copolymers at fully extended conformation. However,
the copolymer PVAc(11200)-b-PVNDc(38300) does not form
any stable dispersion in acetone. It is dissolved in good solvent
such as THF but immediately precipitates upon addition of
acetone, possibly because of longer block of PVNDc.
The bulk property of the block copolymers is investigated
using DSC. The results are shown in Figure 15 together with
those of hompolymers PVAc and PVNDc. The block copoly-
mer clearly displays two glass-transition temperatures (Tg) at
around 0 and 42 °C, corresponding to the segments of PVNDc
and PVAc, respectively. This demonstrates that microphase
separation occurred in the bulk sample of block copolymer.
For the hydrolyzed products, PVOH-b-PVNDc, a melting
peak can be clearly seen at ∼215 °C, which is slightly lower
than that of PVOH homopolymer (Figure 15b). It can be
concluded that the domain of PVOH after phase separation
crystallizes into less perfect morphology.
spectra of block copolymer before and after hydrolysis; 1H
NMR of PVAc with low molecular weight (2400 g/mol). This
material is available free of charge via the Internet at http://
pubs.acs.org.
References and Notes
(1) (a) Chiefari, J.; Chong, Y. K.; Ercole, F.; Krstina, J.; Jeffery, J.; Le,
T. P. T.; Mayadunne, R. T. A.; Meijs, G. F.; Moad, C. L.; Moad,
G.; Rizzardo, E.; Thang, S. H. Macromolecules 1998, 31, 5559–
5562. (b) Le, T. P. T.; Moad, G.; Rizzardo, E.; Thang, S. H. PCT Int.
Appl. WO 98/01478, 1998. (c) Rizzardo, E.; Thang, S. H.; Moad, G.
PCT Int. Appl. WO 99/05099, 1998.
(2) Here are some examples: (a) Chong, Y. K.; Le, T. P. T.; Moad, G.;
Rizzardo, E.; Thang, S. H. Macromolecules 1999, 32, 2071–2074.
(b) Mayadunne, R. T. A.; Rizzardo, E.; Chiefari, J.; Krstina, J.; Moad,
G.; Postma, A.; Thang, S. H. Macromolecules 2000, 33, 243–245. (c)
Stenzel-Rosenbaum, M.; Davis, T. P.; Chen, V.; Fane, A. G. J. Polym.
Sci., Part A: Polym. Chem. 2001, 39, 2777–2783. For reviews see: (d)
Moad, G.; Rizzardo, E.; Thang, S. H. Polymer 2008, 49, 1079–1131.
(e) Favier, A.; Charreyre, M. Macromol. Rapid Commun. 2006, 27,
653–692.
(3) (a) Charmot, D.; Corpart, P.; Adam, H.; Zard, S. Z.; Biadatti, T.;
Bouhadir, G. Macromol. Symp. 2000, 150, 23–32. (b) Corpart, P.;
Charmot, D.; Biadatti, T.; Zard, S. Z.; Michelet, D. PCT Int. Appl. WO
98/58974, 1998.
(4) For a review, see: Perrier, S.; Takolpuckdee, P. J. Polym. Sci., Part
A: Polym. Chem. 2005, 43, 5347–5393.
(5) (a) Destarac, M.; Brochon, C.; Catala, J.-M.; Wilczewska, A.;
Zard, S. Z. Macromol. Chem. Phys. 2002, 203, 2281–2289. (b)
Destarac, M.; Bzducha, W.; Taton, D.; Gauthier-Gillaizeau, I.; Zard,
S. Z. Macromol. Rapid Commun. 2002, 23, 1049–1054. (c) Adamy,
M.; van Herk, A. M.; Destarac, M.; Monteiro, M. J. Macromolecules
2003, 36, 2293–2301.
(6) (a) Simms, R. W.;Davis, T. P.;Cunningham, M. F. Macromol. Rapid
Commun. 2005, 26, 592–596. (b) Boschmann, D.; Vana, P. Polym. Bull.
2005, 53, 231–242. (c) Stenzel, M. H.; Davis, T. P.; Barner-Kowollik, C.
Chem. Commun. 2004, 1546–1547. (d) Bernard, J.; Favier, A.; Davis,
T. P.; Barner-Kowollik, C.; Stenzel, M. H. Polymer 2006, 47, 1073–1080.
(7) Stenzel, M. H.; Cummins, L.; Roberts, G. E.; Davis, T. P.; Vana,
P.; Barner-Kowollik, C. Macromol. Chem. Phys. 2003, 204, 1160–
1168.
(8) Favier, A.; Barner-Kowollik, C.; Davis, T. P.; Stenzel, M. H.
Macromol. Chem. Phys. 2004, 205, 925–936.
(9) Bernard, J.; Favier, A.; Zhang, L.; Nilasaroya, A.; Davis, T. P.;
Barner-Kowollik, C.; Stenzel, M. H. Macromolecules 2005, 38,
5475–5484.
(10) Coote, M. L.; Radom, L. Macromolecules 2004, 37, 590–596.
(11) Fleet, R.; McLeary, J. B.; Grumel, V.; Weber, W. G.; Matahwa, H.;
Sanderson, R. D. Macromol. Symp. 2007, 255, 8–19.
(12) Russum, J. P.; Barbre, N. D.; Jones, C. W.; Schork, F. J. J. Polym.
Sci.; Part A: Polym. Chem. 2005, 43, 2188–2193.
(13) (a) Tong, Y.; Dong, Y.; Du, F.; Li, Z. Macromolecules 2008, 41,
7339–7346. (b) Tong, Y.; Wang, R.; Xu, N.; Du, F.; Li, Z. J. Polym.
Sci., Part A: Polym. Chem. 2009, 47, 4494–4504.
Conclusions
Radical polymerization of VAc in the presence of DIP under-
goes a RAFT process mediated by xanthate formed in situ via a
series of radical process. Two kinds of xanthates play the role of
RAFT/MADIX agents, that is, S-(cyano)isopropyl xanthate (3)
and diisopropyl dithiocarbonate (8). The presence of 8 is specific
for VAc, formed through intramolecular rearrangement of the
intermediate. After the induction period, the polymerization
proceeds in a controlled/“living” style because of the presence
of 3 and 8, the former being the main RAFT/MADIX agent.
Block copolymers are successfully synthesized by sequential
polymerization of VAc and VNDc. The length of blocks can be
tuned by changing the molar ratio of the second monomer,
VNDc, to the first block PVAc. The block copolymer is selec-
tively hydrolyzed to prepare well-defined PVOH-b-PVNDc pos-
sessing semicrystalline PVOH segment. The block copolymer
before hydrolysis aggregates into micelles in acetone, a selective
solvent of PVAc, and undergoes microphase separation in bulk
state. For the hydrolyzed block copolymer, the melting tempera-
ture is observed at 215 °C for PVOH domain.
(14) Moad, G.; Rizzardo, E.; Thang, S. H. Aust. J. Chem. 2009, 62,
1402–1472.
(15) Barner-Kowollik, C.; Perrier, S. J. Polym. Sci., Part A: Polym.
Chem. 2008, 46, 5715–5723.
(16) (a) Vosloo, J. J.; De Wet-Roos, D.; Tonge, M. P.; Sanderson, R. D.
Macromolecules 2002, 35, 4894–4902. (b) Sprong, E.; De Wet-Roos,
D.; Tonge, M. P.; Sanderson, R. D. J. Polym. Sci., Part A: Polym.
Chem. 2003, 41, 223–235.
(17) Bouhadir, G.; Legrand, N.; Quiclet-Sire, B.; Zard, S. Z. Tetrahe-
dron Lett. 1999, 40, 277–280.
(18) Thang, S. H.; Chong, Y. K.; Mayadunne, R. T. A.; Moad, G.;
Rizzardo, E. Tetrahedron Lett. 1999, 40, 2435–2438.
(19) Zhu, J.; Zhu, X.; Cheng, Z.; Liu, F.; Lu, J. Polymer 2002, 43, 7037–
7042.
(20) Liu, X.; Zhang, G.; Li, B.; Bai, Y.; Pan, D.; Li, Y. Eur. Polym. J.
2008, 44, 1200–1208.
(21) (a) Niwa, M.; Matsumoto, T.; Shimada, Y.; Matsui, Y. Sci. Eng.
Rev. Doshisha Univ. 1986, 26, 219. (b) Niwa, M.; Matsumoto, T.;
Izumi, H. J. Macromol. Sci., Chem. 1987, 24, 567–585. (c) Niwa, M.;
Sako, Y.; Shimizu, M. J. Macromol. Sci., Chem. 1987, 24, 1315–1332.
(22) Lalevee, J.; El-Roz, M.; Allonas, X.; Fouassier, J. P. J. Polym. Sci.;
Part A: Polym. Chem. 2007, 45, 2436–2442.
Acknowledgment. This work is subsidized by NSFC
(20574009) and the National Basic Research Program of China
(2005CB623800). J.H. thanks the helpful discussions with Pro-
fessor Ewald Daltrozzo on the measurements and results of
NMR and MS spectroscopies.
Supporting Information Available: GC-MS of compound 3;
the complete fragmentation scheme of 8 (P300) and 6 (P254); IR

4510 Macromolecules, Vol. 43, No. 10, 2010
Gu et al.
(23) Colombani, D. Prog. Polym. Sci. 1997, 22, 1649–1720.
(24) Sebenik, A. Prog. Polym. Sci. 1998, 23, 875–917.
(25) Monteiro, M. J.; Subramaniam, N.; Taylor, J. R.; Pham, B. T. T.;
Tonge, M. P.; Gilbert, R. G. Polymer 2001, 42, 2403–2411.
(26) Unzue, M. J.; Urretabizkaia, A; Asua, J. M. J. Appl. Polym. Sci.
2000, 78, 475–485.
(32) (a) McLeary, J. B.; Calitz, F. M.; McKenzie, J. M.; Tonge, M. P.;
Sanderson, R. D.; Klumperman, B. Macromolecules 2004, 37, 2383–
2394. (b) McLeary, J. B.; Calitz, F. M.; McKenzie, J. M.; Tonge, M. P.;
Sanderson, R. D.; Klumperman, B. Macromolecules 2005, 38, 3151–3161.
(33) Barner-Kowollik, C.; Quinn, J. F.; Nguyen, T. L. U.; Heuts, J. P. A.;
Davis, T. P. Macromolecules 2001, 34, 7849–7857.
(27) (a) Nguyen, T. L. U.; Eagles, K.; Davis, T. P.; Barner-Kowollik, C.;
Stenzel, M. H. J. Polym. Sci.; Part A: Polym. Chem. 2006, 44, 4372–
4383. (b) Nguyen, T. L. U.; Farrugia, B.; Davis, T. P.; Barner-Kowollik,
C.; Stenzel, M. H. J. Polym. Sci.; Part A: Polym. Chem. 2007, 45,
3256–3272.
(34) Shi, L.; Chapman, T. M.; Beckman, E. J. Macromolecules 2003, 36,
2563–2567.
(35) Gareau, Y.; Beauchemin, A. Heterocycles 1998, 48, 2003–2017.
(36) Fandrich, N.; Falkenhagen, J.; Weidner, S. M.; Pfeifer, D.; Staal,
€
B.; Thunemann, A. F.; Laschewsky, A. Macromol. Chem. Phys.
(28) Balic, R.; Gilbert, R. G.; Zammit, M. D.; Davis, T. P.; Miller, C. M.
Macromolecules 1997, 30, 3775–3780.
2010, 211, 869–878.
(37) Pound, G.;Aguesse, F.;McLeary, J. B.;Lange, R. F. M.;Klumperman,
(29) Koukiotis, C.; Sideridou, I. D. Prog. Org. Coat. 2008, 63, 116–122.
(30) Plummer, R.; Goh, Y. K.; Whittaker, A. K; Monteiro, M. J.
Macromolecules 2005, 38, 5352–5355.
(31) Han, X.; Fan, J.; He, J.; Xu, J.; Fan, D.; Yang, Y. Macromolecules
2007, 40, 5618–5624.
B. Macromolecules 2007, 40, 8861–8871.
(38) Pound, G.; McLeary, J. B.; McKenzie, J. M.; Lange, R. F. M.;
Klumperman, B. Macromolecules 2006, 39, 7796–7797.
(39) Debuigne, A.; Willet, N.; Jerome, R.; Detrembleur, C. Macromo-
lecules 2007, 40, 7111–7118.