Phosphonate-terminated poly(vinyl acetate) synthesized by RAFT/MADIX polymerization

Article abstract of DOI:10.1002/pola.25974

Four different xanthates containing either phosphonate or bisphosphonate moieties were synthesized with high degree of purity. These xanthates were used as chain transfer agents (CTA) in the RAFT/MADIX polymerization of vinyl acetate (VAc) to prepare end-capped poly(VAc). The rate of VAc polymerization in the presence of these new CTAs was shown to be similar to that obtained with conventional xanthate, that is, (methyl ethoxycarbonothioyl) sulfanyl acetate. Good control of VAc polymerization was also obtained since the molecular weight increased linearly with monomer conversion for each phosphonate-containing xanthate. Low-PDI values were obtained, ascribed to efficient exchange during RAFT/MADIX polymerization. C_ex value was therefore calculated to about 25, based on RAFT/MADIX of VAc in the presence of rhodixan A1/VAc adduct.

Full text of DOI:10.1002/pola.25974

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Phosphonate-Terminated Poly(vinyl acetate) Synthesized by
RAFT/MADIX Polymerization
P-E. Dufils,1 G. David,1 B. Boutevin,1 G. Woodward,2 G. Otter,2 A. Guinaudeau,3
3
3
`
S. Mazieres, M. Destarac
1Institut Charles Gerhardt., UMR 5253 CNRS, E.N.S. Chimie de Montpellier 8, rue Ecole Normale,
34296 Montpellier Cedex 5, France
2Rhodia Bristol Research and Technical Center, 350 George Patterson Blvd 19007, Bristol, Pennsylvania
3
ꢀ
Laboratoire HFA, CNRS UMR 5623, Universite de Toulouse, 31062 Toulouse cedex 09, France
Correspondence to: G. David (E-mail: ghislain.david@enscm.fr)
Received 5 January 2012; accepted 30 January 2012; published online 23 February 2012
DOI: 10.1002/pola.25974
ABSTRACT: Four different xanthates containing either phospho-
nate or bisphosphonate moieties were synthesized with high
degree of purity. These xanthates were used as chain transfer
agents (CTA) in the RAFT/MADIX polymerization of vinyl ace-
tate (VAc) to prepare end-capped poly(VAc). The rate of VAc
polymerization in the presence of these new CTAs was shown
to be similar to that obtained with conventional xanthate, that
is, (methyl ethoxycarbonothioyl) sulfanyl acetate. Good control
of VAc polymerization was also obtained since the molecular
weight increased linearly with monomer conversion for each
phosphonate-containing xanthate. Low-PDI values were
obtained, ascribed to efficient exchange during RAFT/MADIX
polymerization. Cex value was therefore calculated to about 25,
based on RAFT/MADIX of VAc in the presence of rhodixan A1/
C
V
VAc adduct. 2012 Wiley Periodicals, Inc. J Polym Sci Part A:
Polym Chem 50: 1997–2007, 2012
KEYWORDS: bisphosphonate; heteroatom-containing polymers;
kinetics; poly(vinyl acetate); RAFT/MADIX macromolecular
design by interchange of xanthates (RAFT/MADIX); reversible
addition-fragmentation chain transfer polymerization (RAFT);
xanthate
INTRODUCTION Among phosphorus compounds, phospho-
rus-containing polymers have elicited many interest over
decades.1–4 Polyphosphates and polyphosphonates were first
utilized as very interesting fire retardant additives.2,5–8
Because of their strong adhesion properties, especially
towards metallic substrates, their field of applications
became larger.9,10 They were indeed incorporated as adhe-
sion primers in paint coatings, first as phosphate-type
(meth)acrylate polymers.11,12 New types of phosphonate
(meth)acrylate polymers were developed to substitute the
former ones, because their better resistance towards hydro-
lysis was well established. Moszner et al. also demonstrated
the hydrolytic stability of phosphonic acid-containing acrylic
polymers, compared with the phosphate type polymers, to be
used as self-etching enamel-dentin primer.13–18 Madec and co-
workers19 have also developped a series of new acrylamido-
propylene bisphosphonic acid to be used as self-etch adhesives
(SEAs) in dentistry. These authors demonstrated, by evaluating
the shear bond strentghs of additives, that the bisphosphonic
acid polymers exhibited higher adhesive performance than that
of commercially available primers. Phosphonic polymers were
also recently extended to biomedical applications and also as
polyelectrolyte membranes for fuel cell applications.20,21 Else-
where, biodegradable and biocompatible phosphorus-contain-
ing polymers have been proposed as agents for the control of
CaCO3 crystallization, or for use in tissue engineering and drug
release.22–24 Recently, incorporation of bisphosphonic groups
into phosphonic polymers was performed to enhance their
properties.25 For instance, bisphosphonic acid-containing poly-
mers and espescially nitrogen-containing bisphosphonate were
proved to be excellent antihypercalcemics, that is, therapeutic
agents for stopping bone deterioration and for restoring the
normal calcium balance.26,27
Outside the biomedical sphere, bisphosphonic methacrylate
polymers, obtained by UV-photopolymerization, were shown
to be excellent adhesion promoters and hence led to high per-
formance anticorrosion coatings.28 Interestingly, for the same
amount of phosphonic groups, bisphosphonic-containing
polymers were more efficient (towards corrosion resistance)
compared with phosphonic-containing polymers. Further-
more, chelating ion-exchange resins based on bisphosphonic-
containing polymers showed high capacity for uranium
extraction, that is, recovery from phosphoric acid solutions,
as well as for removal of metal pollutants such as Cd(II) or
Cr(III).29–31
C
V
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The properties of phosphonic (co)polymers in applications
are strongly related to both concentration and controlled
incorporation of phosphonate units. As phosphonate mono-
mers are usually much more expensive than the other como-
nomers, it appears that their incorporation is key to optimize
the cost/performance balance of the copolymer. For instance,
in conventional radical polymerization, the copolymerization
of phosphonate-containing methacrylates with methacrylate
comonomers led to statistical phosphonic copolymers where
phosphonate groups were statistically distributed along the
polymeric backbone.32 A first step towards control of the
chain architecture of phosphonic polymers in radical polymer-
ization was achieved by means of telomerization reactions in
the presence of phosphonate33 or phosphite34 transfer agents.
duce PVAc of precise architectures with controlled Mn and
narrow molar mass distributions.48–54
Hence, the aim of this study is to propose end-capped PVAc
with phosphonate or bisphosphonate moities through RAFT/
MADIX polymerization. This chain-end functionality can be
obtained by the use of functional xanthates, that is, bearing
either phosphonate or bisphosphonate groups. The first part
of this article is devoted to the synthesis of the xanthates.
Then their efficiency as chain transfer agents (CTAs) in
RAFT/MADIX process will be evaluated and finally a special
care for chain-end functionality study will be taken.
RESULTS AND DISCUSSION
Synthesis of Phosphonate CTAs
In spite of the advent of controlled radical polymerizations
(CRP) techniques, a few synthetic strategies were proposed
to precisely control the polymerization of phosphonate
monomers, in particular methacrylate and vinyl phosphonate
monomers. For instance, David et al.35 performed atom
transfer radical polymerization (ATRP) of dimethyl(metha-
cryloyloxy)methyl phosphonate and concluded in poor
control in terms of molecular weight and livingness with
monomer conversion limited to 20%. In CRP of phospho-
nate-containing methacrylate monomers by degenerative
transfer (DT) processes, a peculiar behiavor was observed
where an unexpectedly radical loss was observed during the
DT process.36 In this particular article, the authors showed
that the reversible addition-fragmentation chain transfer
polymerization (RAFT) process did not afford any polymer-
ization of the monomer, whereas reverse iodine transfer
polymerization (RITP) led to a quite good control.
A series of four different xanthates (xanthates 1–4 in Table 1)
was synthesized with phosphonate moieties to prepare end-
functionalized poly(vinyl acetate). These CTAs were designed
to efficiently introduce at the chain end triethyl phosphonoa-
cetate (xanthate 1), tetraethyl methylene bisphosphonate
(xanthate 2), or tetraisopropyl methylene bisphosphonate
(xanthates 3 and 4) moieties. Xanthates 3 and 4 differ in
their stabilizing Z-group (ethoxy for xanthate 3 and isopro-
pyloxy for xanthate 4), which may influence the RAFT/
MADIX polymerization of VAc. Indeed, Davis et al.54 per-
formed the synthesis of both (ethoxycarbonothioyl)sulfanyl
acetate and (isopropoxycarbonothioyl)sulfanyl acetate CTAs
and observed better efficiency for the former CTA (lower
polydispersities and higher rates of polymerization).
Xanthate 1 was obtained in a three-step reaction, according
to Scheme 1. This synthesis was already described by Mc
55
Kenna et al.
and proceeds via a chloration/dechloration of
the ethyl 2-diethylphosphonoacetate precursor. Finally, the
monochloride resulting compound can react with the potas-
sium xanthate salt at 0ꢀC to quantitatively afford the xan-
thate 1. The 1H NMR spectrum (Fig. 1) of xanthate 1 shows
a high degree of purity (higher than 99%).
CRP of vinyl phosphonic acid (VPA) was carried out using
DT processes such as iodine transfer polymerization (ITP)
RAFT. In the case of ITP, only irreversible transfer—that is,
telomerization—took place instead of DT.37,38 In contrast,
RAFT/MADIX (standing for macromolecular design by inter-
change of xanthates) polymerization of VPA using O-ethyl
xanthate transfer agents RAFT/MADIX led to the synthesis of
poly(VPA)-based block copolymers.39,40
By using a procedure previously described by Zard et al.56
(Scheme 2), xanthates 2 to 4 were obtained in moderate
yields (42, 43, and 37% for xanthates 2, 3, and 4, respec-
tively) as a yellow oil with a high purity degree (higher than
99%) as confirmed by 1H NMR (see example of xanthate 3,
Fig. 2). Interestingly, 1H NMR of the four xanthates may
afford an estimation of their ability to undergo b-fragmenta-
tion by looking at the shift of the protons on the carbon adja-
cent to the sulphur in the leaving moiety. This shift (Table 1)
decreases from 4.91 to 4.63 going from xanthate 1 to 4 indicat-
ing that the replacement of the ester group by a phosphonate
group may induce a lower stability of the generated radical.
The same consideration could be applied to xanthates 2 and 3,
that is, replacing the ethyl group of the phosphonate by isopro-
pyl group. Hence, a kinetic study of the RAFT/MADIX polymer-
ization of VAc in the presence of xanthates 1 to 4 was carried
out to assess the reactivity of these new CTAs.
This short overview clearly outlines that the strategies to
control the phosphorus-containing polymer architecture are
very limited. Furthermore, to our knowledge, no study men-
tioned the controlled incorporation of phosphonate moities
into polyvinylacetate (PVAc), whereas PVAc and related
copolymers are very important polymers as their industrial
applications are wide ranging from paints, adhesives, con-
struction materials, to additives for pharmaceuticals.41,42
When hydrolyzed in polyvinyl alcohol (PVA), it becomes bio-
degradable and water-soluble. Therefore, the controlled
incorporation of phosphonate moities into PVAc may be of
great interest to combine the aforementioned properties of
phosphonic polymers to those of PVAc and PVAs. In recent
years, CRP of vinyl acetate (VAc) has been investigated to
such an extent that quite significant progresses could be
accomplished.43–46 It is now well established that RAFT/
MADIX47 is the most straightforward CRP technique to pro-
Polymerization of VAc with Xanthates 0 to 4
Bulk polymerization of VAc was initiated by the AIBN initia-
tor at 70ꢀC in the presence of xanthates 1 to 4, with a
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TABLE 1 Structure of Xanthates used in the RAFT/MADIX Polymerization of VAc
NMR Chemical Shift (ppm)
Xanthate
0
Structure
MW (g/mol)
194
Yield (%)
–
1H (S-CH)
31P
–
–
1
2
344
408
37
42
4.91 (d, J ¼ 21.7 Hz)
14.67
16.09
4.74 (t, J ¼ 21.6 Hz)
3
4
464
478
43
37
4.63 (t, J ¼ 22.2 Hz)
14.22
15.46
4.63 (t, J ¼ 21.7 Hz)
[AIBN]0 to [xanthate]0 ratio kept equal to 0.05. The kinetics
of polymerization was investigated and the macromolecular
characteristics of the obtained polymers were determined as
a means to determine the level of control of VAc polymeriza-
tion. (Methyl ethoxycarbonothioyl) sulfanyl acetate of general
structure MeO(CO)CH2-S(C¼¼S)OEt (X0), which was thor-
oughly studied in the past for VAc polymerization by Stenzel
et al.,54 was taken as a basis for comparison. First of all, the
effect of the nature of the xanthate on the overall rate of
polymerization was studied for an initial xanthate concentra-
tion equal to 4.7 ꢁ 10ꢂ1 mol/L, by following the monomer
to polymer conversion (CVAc) by 1H NMR. From Figure 3,
which shows the corresponding CVAc versus time plot, it
appears that the xanthates 1, 2, 3, and 4 have a similar effect
on the rate of polymerization with a characteristic induction
period of about 30 min followed by a polymerization which is
nearly completed after 6 h of reaction. The rate of polymeriza-
tion mediated by the reference xanthate X0 was similar to
those observed with the other xanthates. In contrast, the
induction period was noticeably shorter. The latter result was
explained by the lower stability of the methoxycarbonylmethyl
radical than for the other leaving radicals of the series, induc-
ing a lower selectivity in the initialization stage of the poly-
merization.57 However, at 70ꢀC, no differences in rates were
revealed between ethoxy (X0, X1, X2, X3) or isopropoxy (X4) Z
54
groups. Stenzel et al.
pointed out slight differences in
behavior for ethoxy and isopropoxy Z groups when polymer-
izations were carried out at 60ꢀC with xanthates bearing a
methoxycarbonylmethyl leaving group. It was concluded that
a shorter induction period and faster polymerization rates
were obtained with Z ¼ ethoxy compared with the slightly
less electron-withdrawing isopropoxy group, whereas no no-
ticeable differences in polydispersities (PDIs) were reported.
SCHEME 1 Synthesis of xanthate 1.
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FIGURE 1 1H NMR spectrum (CDCl3) of xanthate 1.
Number-average molecular weights (Mn) and PDIs were fol-
lowed during RAFT/MADIX polymerization of VAc mediated
with xanthates 1 to 4 for xanthate concentrations of 4.6 ꢁ
10ꢂ2 mol/L, 9.3 ꢁ 10ꢂ2 mol/L, 1.8 ꢁ 10ꢂ1 mol/L, and 4.7 ꢁ
10ꢂ1 mol/L which correspond to theoretical Mn of 20,000,
10,000, 5000, and 2000 at complete monomer conversion,
respectively. Here again, the results were compared with those
obtained when using the xanthate X0 as a reference. The Mn
and PDI evolution profiles are gathered in Figures 4 to 7.
higher than 95%. Finally, for [CTA] ¼ 4.7 ꢁ 10ꢂ1 mol/L
(Mntheo ¼ 2000 g/mol), the PDI values remained below 1.4
up to complete conversion. Similar results were obtained
with the xanthates 2 and 3 (Fig. 6), confirming the former
observations from the Hammett’s molecular descriptors.
The PDIs values, obtained at half and complete conversion
for the polymerization mediated with the four different xan-
thates at four different targeted molecular weights, are dis-
played in the following Table 2.
Figures 5 and 7 display the evolution of the molecular
weight Mn with monomer conversion for xanthates 1 and 4,
respectively. For both CTAs, the molecular weight increase
linearly with the monomer conversion, and the experimental
values were in very good agreement with the theoretical
ones. Whatever the nature of the CTA, the PDIs of the
obtained PVAc remained below 1.4 up to 70–80 % monomer
conversion. For [CTA] ¼ 9.3 ꢁ 10ꢂ2 and 4.6 ꢁ 10ꢂ2 mol/L
(respectively Mntheo ¼ 10,000 and 20,000 g/mol), the PDI
values increase up to 1.8 when the monomer to polymer
conversion exceeds 80%. For [CTA] ¼ 1.8 ꢁ 10ꢂ1 mol/L
(Mntheo ¼ 5000 g/mol), the PDI values exceed the limit of
1.4 only at the very end of the polymerization for conversion
The first observation is, as already expressed above, that the
PDI values are increasing as the conversion is increasing and
the difference between half and complete conversion is
increasing as the targeted molecular weight at complete con-
version is increasing. Such a behavior has also been observed
for previously reported RAFT/MADIX polymerizations48 and it
could be attributed to the irreversible transfer reactions to
monomer and polymer involving the very reactive VAc radi-
cal.58 Yamago and coworkers59 have observed that head-to-
head VAc addition was significant on propagation in organo-
tellurium-mediated living polymerization, forming a primary
alkyl chain-end ACH2-TeCH3 adduct. The activation was too
slow to yield low-polydispersity polymers, explaining why
they observed unsatisfactory PDI’s at high degree of polymer-
ization. Recently, Pouget et al.60 have also observed similar
head-to-head VAc addition in RITP. Although there is no
experimental proof of head-to-head VAc addition in RAFT/
MADIX polymerization, it is conceivable to consider that head-
to-head VAc addition could also happen in the present case,
and so this assumption could be also considered to explain
the increase of the PDI values at high degree of conversion.
SCHEME 2 Synthesis of xanthates 2–4.
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FIGURE 2 1H NMR spectrum (CDCl3) of xanthate 3.
The low-PDI values are generally ascribed to a fast xanthate
inter-chain exchange, which can be readily characterized by a
very high Cex value. It is quite difficult to reach the Cex value.
The VAc monoadduct was used as first approximation for mon-
itoring the ability of the xanthate chain-end to exchange. First,
the xanthate X5, that is, VAc monoadduct, was synthesized by
reaction of Rhodixan A1, used in large excess, with VAc
(Scheme 3). Then, RAFT/MADIX of VAc in the presence of such
adduct was performed and monomer conversion followed over
time. Thus, Ln ([VAc-X5]) was plotted against Ln ([VAc]), the
slope of which gives Cex value of about 25 (Fig. 8). This result
reveals that PDI values should be lower than 1.1 (PDI ¼ 1 þ
1/ Cex) at the end of polymerization. Higher PDI values would
then be the result of other events than slow inter-chain
exchange, such as transfer reactions or reinitiation.
tionalize PVAc with phosphonate/bisphosphonate chain-end,
that is, most of the chains being initiated by the R group of
the xanthates. Only MALDI-TOF analysis of PVAc may defini-
tively assess the chain end functionality61. PVAc with low
Mn (<5000 g/mol), obtained with xanthates 1 to 4, were
Phosphonate End-Group Analysis
Despite a potential low rate of head-to-head VAc addition,
the control of VAc polymerization was demonstrated with
xanthates 1 to 4. The aim of this study is to efficiently func-
FIGURE 4 Evolution of Mn and PDI in RAFT/MADIX polymeriza-
tion of VAc initiated by AIBN at 70ꢀC during 480 min and medi-
ated by X0, for different initial X0 concentrations. AIBN]0/
[VAc]0 ¼ 0.05. (a) Mn and (b) PDI.
FIGURE 3 Evolution of vinyl acetate conversion with time in pol-
ymerizations performed at 70ꢀC with a series of xanthates. [Xan-
thate]0 ¼ 4.7 ꢁ 10ꢂ1 mol/L and [AIBN]0 ¼ 2.35 ꢁ 10ꢂ2 mol/L.
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bearing the R-group of the starting transfer agent (i.e., phos-
phonate moiety) at one end and its thiocarbonylthio moiety
at the other end.
EXPERIMENTAL
Materials
O-ethyl xanthic potassium salt (98%) was purchased from Lan-
caster. Methyl bromoacetate (97%), diethyl ethoxycarbonylme-
thylphosphonate (98%), tetraethyl methylene diphosphonate
(97%), iodine (99.8%), isopropylxanthic disulfide (95%), and
sodium hydride (60% dispersion in mineral oil) were pur-
chased from Aldrich. Tetraisopropyl methylene diphosphonate
(98%) was provided by RHODIA. All the reactants were used
without further purification. 1,2-Dichloroethane (DCE, Acros,
99%), O-ethyl-S-(1-methoxycarbonyl)ethyldithiocarbonate (Rho-
dixan A1, supplied by Rhodia), and dilauroyl peroxide (DLP,
Acros, 99%) were used as received. VAc (Aldrich 99.9%) was
filtered prior to passing through a column of basic aluminium
oxide to remove inhibitors. 2,20-Azobisisobutyronitrile (AIBN)
(Aldrich 99%) was recrystallized twice from methanol.
Characterization
1H nuclear magnetic resonance (NMR) spectra were
recorded at room temperature on Bruker AC 400 instrument,
FIGURE 5 Evolution of Mn and PDI in RAFT/MADIX polymeriza-
tion of VAc initiated by AIBN at 70ꢀC during 480 min and medi-
ated by xanthate X1, for different initial concentrations of X1.
[AIBN]0/[VAc]0 ¼ 0.05. (a) Mn and (b) PDI.
analyzed by MALDI-TOF; Figure 9 shows the spectrum
obtained with xanthate 1. A series of major peak can be iden-
tified which correspond to a sodium ion adduct of PVAc poly-
meric chain, end capped by the acetophosphonate moiety of
the CTA 1 in a position and the thiocarbonylthio moiety in x.
To identify minor peaks, enlargements must be done.
Figure 10 shows enlargements, in the m/z 1390–1500 u.a.
area, of PVAc obtained with xanthate 1 at three different Mn,
that is, 1960, 4340, and 4750 g/mol. As expected, the most
intense series peak at 1399.5 u.a., for instance, corresponds
to the main species. A second series of minor peaks (approx-
imately 10% of the main peaks) appears between the main
patterns. The m/z values (e.g., m/z 1451.663) corresponds
to poly(vinyl acetate) terminated by a proton in x position
(instead of the thiocarbonylthio moiety), corresponding to
dead polymers. Surprisingly, the species was not observed at
higher molecular weight (4750 g/mol). As the concentration
of the dead polymers is supposed to increase with the
increase of the monomer conversion, the absence of this spe-
cies at higher Mn suggests that this species could be gener-
ated during the analysis.
FIGURE 6 Evolution of Mn and PDI in RAFT/MADIX polymeriza-
tion of VAc initiated by AIBN at 70ꢀC during 480 min and medi-
ated by xanthate X3, for different initial concentrations of X3.
[AIBN]0/[VAc]0 ¼ 0.05. (a) Mn and (b) PDI.
In conclusion, the MALDI-TOF analysis of PVAc synthesized
in the presence of the xanthates 1 to 4 showed that the sam-
ples were mainly composed of living polymers (PVAC 1)
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SCHEME 3 Synthesis of xanthate X5 (Rhodixan A1/VAc
adduct).
10ꢂ5 dL/g and a ¼ 0.70.62 The Mark-Houwink parameters
for polystyrene used to effect the universal calibration were
K ¼ 14.1 ꢁ 10ꢂ 5 dL/g and a ¼ 0.70.63
P(VAc) samples were analyzed by matrix-assisted laser
desorption ionization time-of-flight mass spectrometry
(MALDI-TOF MS) performed using a PerSeptive Biosystems
Voyager Elite (Framingham, MA). This instrument is equipped
with a nitrogen laser (337 nm; 3 ns pulse), a delayed extrac-
tion, and a reflector. It was operated at an accelerating poten-
tial of 25 kV in linear mode. The MALDI mass spectra repre-
sent averages over 2048 consecutive laser shots (3 Hz
repetition rate). The polymer solutions (2–5 g/L) were pre-
pared in THF. The [4-(4-nitrophenylazo)-resorcinol] matrix
was also dissolved in THF (25 g/L). A 10 lL portion of the
polymer solution was mixed with 20 lL of the matrix solu-
tion. A sodium chloride solution [10 lL of a solution at
20 g/L in a mixture water/ethanol (10/90)] was finally
added to favor ionization by cation attachment. A 1 lL por-
tion of the final solution was deposited onto the sample tar-
get and allowed to dry in air at room temperature. Polysty-
rene standards (purchased from Polymer Standards Service)
were used to calibrate the mass scale using the two point
calibration software 3.07.1 from PerSeptive Biosystems.
FIGURE 7 Evolution of Mn and PDI in RAFT/MADIX polymeriza-
tion of VAc initiated by AIBN at 70ꢀC during 480 min and medi-
ated by xanthate 4, for different initial concentrations of 4.
[AIBN]0/[VAc]0 ¼ 0.05. (a) Mn and (b) PDI.
Synthesis of Xanthates
in d6-DMSO or D2O and with tetramethylsilane (TMS) as the
reference. In the figures and discussion below, the letters s,
d, t, q and m are abbreviations for singlet, doublet, triplet,
quintet, and multiplet, respectively. Coupling constants are
given in Hertz (Hz) and chemical shifts in ppm. Molecular
weights and polydispersity indexes were determined on
crude samples by gel permeation chromatography (GPC)
using a Spectra Physics Instruments SP8810 pump equipped
with two 300 mm PL-Gel 5 lm mixed-C columns (Polymer
Laboratories) and a Shodex Rise-61 refractometer detector.
Tetrahydrofuran (HPLC grade) was used as eluant (1.0 mL/
min) at 30ꢀC, after filtration over PTFE 0.2 lm filters. The
obtained molecular weights were corrected via the universal
calibration using the Mark-Houwink parameters K ¼ 16 ꢁ
Synthesis of Xanthate 1 Ethyl 2-(diethoxyphosphoryl)-
2-(ethoxycarbonothioylthio)acetate
In a round-bottomed flask, 20 mL (100 mmol) of ethyl
2-diethylphosphono acetate was added dropwise to house-
hold bleach (sodium hypochlorite, 5 eq. 235 mL, 0.5 mol),
whose pH was adjusted to 7 with HCl (3N). The mixture was
stirred at 0ꢀC. When the addition was finished, the mixture
was stirred overnight at room temperature. The solution was
extracted with hexane. The organic phase was collected and
washed with water saturated in NaCl, dried over MgSO4, fil-
tered, and the solvent were removed under reduced pressure.
Ethyl-2,2-dichloro-2-diethylphosphonoacetate was obtained
as colorless oil. Then, in a round-bottomed flask, 17.3 g
(59 mmol) of ethyl 2,2-dichloro-2-diethylphosphonoacetate
TABLE 2 Evolution of PDI Values at Half and Complete Conversion for VAc Polymerization
Mediated with the Four Different Xanthates at Four Different Targeted Molecular Weights
Mn theo (g/mol)
CVAc (%)
2000
5000
10,000
20,000
ꢃ 50
> 90
ꢃ 50
> 90
ꢃ 50
> 90
ꢃ 50
> 90
Xanthate
X1
X2
X3
X4
1.22
1.17
1.24
1.34
1.21
1.28
1.32
1.38
1.28
–
1.48
–
1.45b
1.38
1.42
1.37c
1.40
1.72a
1.74
1.72
1.78
1.48
–
1.93
–
1.40
1.28
1.43
1.54
1.82
1.86
1.62
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evaporated off. The residue was dissolved in 60 mL of water
and washed with dichloromethane. The organic phase was
collected, dried over MgSO4, filtered, and the solvent was
removed under reduced pressure. The residue was purified
by silica gel (SDS, 70–200 lm) column chromatography
(eluant: ethyl acetate/n-hexane 70/30). The xanthate 1 was
obtained with 43% yield.
1H NMR (CDCl3, 400 MHz): 1.27 (t, J ¼ 7.07 Hz, 3H,
C(S)OCH2CH3), 1.28–1.39 (m, 9H, OCH2CH3), 1.37 (t, J ¼
7.07 Hz, 3H, C(O)OCH2CH3), 4.16–4.25 (m, 6H, OCH2CH3),
4.60 (dq, J ¼ 7.07 Hz, 2H, OCH2CH3), 4.91 (d, J ¼ 21.7 Hz,
1H, CHP). 31P NMR (CDCl3, 162 MHz): 14.67. 13C NMR
(CDCl3,
100
MHz):
13.49
(C(S)OCH2CH3),
13.89
(C(O)OCH2CH3), 16.10 (POCH2CH3),16.17 (POCH2CH3), 49.79
(d, J ¼ 132.5 Hz, CH-P), 62.54 (C(O)OCH2CH3), 63.87 (d, J ¼
6.6 Hz, POCH2CH3), 64.07 (d, J ¼ 6.6 Hz, POCH2CH3), 71.08
(C(S)OCH2CH3), 165.71 (C¼¼O), 210.34 (C¼¼S).
FIGURE 8 Method of kinetic equations used in the RAFT/
MADIX polymerization of VAc initiated by AIBN at 70ꢀC during
480 min and mediated by xanthate X5, [VAc]0 ¼ 10.5 mol/L,
[X5]0 ¼ 9.38 ꢁ 10ꢂ2 mol/L, [AIBN]0 ¼ 9.31ꢁ 10ꢂ2 mol/L.
Synthesis of Xanthates 2 to 4
The typical procedure for the synthesis of xanthates 2 to 4 is
as following and described for xanthate 4 as an example:
was dissolved in 100 mL of ethanol and a Na2SO3 solution in
water (200 mL, 0.5 N) was then added dropwise. The mix-
ture was stirred at 0ꢀC. When the addition was finished, the
mixture was vigorously stirred for 10 min. The solution was
extracted with dichloromethane. The organic phase was col-
lected and washed with water saturated in NaCl, dried over
MgSO4, filtered, and the solvent were removed under
reduced pressure. Ethyl-2-chloro-2-diethylphosphonoacetate
was obtained as colorless oil. Finally, in a round-bottomed
flask, 15.2 g (59 mmol) of ethyl 2-dichloro-2-diethylphospho-
noacetate was dissolved in 50 mL of dry acetone and 8.10 g
(50 mmol) of the commercially available O-ethyl xanthic acid
potassium salt, dissolved in 150 mL of dry acetone, was then
added dropwise. The mixture was stirred at 0ꢀC during the
addition and at room temperature overnight. The white pre-
cipitate of KBr was isolated by filtration and acetone was
To a solution of tetraisopropyl methylene bisphosphonate
(1.709 g, 5 mmol) in anhydrous THF at 0ꢀC under argon, a
60% NaH dispersion in mineral oil (0.39 g, 5 mmol) was
added dropwise. When the evolution of hydrogen ceased, the
reaction mixture was cooled down to ꢂ78ꢀC and a solution
of bisisopropoxy thiocarbonyl disulfane (1.202 g, 5 mmol) in
anhydrous THF was added. The reaction mixture was then
slowly warmed to room temperature and concentrated
under reduced pressure and the residue was solubilized
with 100 mL of diethyl ether. The solution was washed with
a 0.1 mol/L HCl solution (3 ꢁ 35 mL). The organic phase
was dried over MgSO4, filtered, and the solvent were
removed under reduced pressure. The residue was purified
by silica gel (SDS, 70–200 lm) column chromatography
FIGURE 9 MALDI-TOF spectrum of PVAc mediated with xanthate X1 [Mn (GPC) ¼ 1000 g/mol].
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FIGURE 10 MALDI-TOF spectrum of PVAc mediated with xanthate 1 [Mn (GPC) ¼ 1960 g/mol, 4340 g/mol, and 4750 g/mol).
(eluant: ethyl acetate/n-hexane 70/30). The xanthate 4 was
obtained with 37% yield.
Synthesis of Xanthate 5 (Rhodixan A1/VAc adduct)
Vinyl acetate (1.6 g, 1.85 ꢁ 10ꢂ2 mol), Rhodixan A1 (3.5 g,
16.8 mmol), and 1,2-dichloroethane (1.98 g) were introduced
in a 25-mL Schlenk flask. The solution was heated to reflux
(85ꢀC) under stirring during 7 h. 5 mol % of dilauryl perox-
ide relative to Rhodixan A1 was added every 90 min up to
25 mol %. The solvent was removed by evaporation under
vacuum. A 30% yield of the expected adduct was obtained
after purification by column chromatography (eluant: ethyl
Xanthate 2 (Ethoxycarbonothioyl)sulfanyl tetraethyl
methylenediphosphonate
1H NMR (CDCl3, 400 MHz): d ¼ 1.31 (t, P(O)OCH2CH3), 1.32
(t, P(O)OCH2CH3), 1.44 (t, J ¼ 7 Hz, 3 H, C(S)OCH2ACH3),
4.17–4.29 (m, 8 H, POCH2CH3), 4.69 (q, 2 H, C(S)OCH2ACH3),
4.86 (t, 1 H, J ¼ 21.7 Hz, 1 H, CH-P). 31P NMR (CDCl3, 162
MHz): d ¼ 16.09. 13C NMR (CDCl3, 100 MHz): d ¼ 13.49
(C(S)OCH2CH3), 16.10 (P(O)OCH2CH3), 16.17 (P(O)OCH2CH3),
43.21 (t, J ¼ 138.5 Hz, CH-P), 63.87 (d, J ¼ 6.6 Hz,
P(O)OCH2CH3), 64.07 (d, J ¼ 6.6 Hz, POCH2CH3), 71.47
(C(S)OCH2CH3), 210.34 (C¼¼S).
1
acetate/cyclohexane 20/80). H NMR (CDCl3, 400 MHz): d ¼
6.66 (t, ASCSCHCH2A, 1H), 4.62 (q, AS¼¼COCH2CH3, 2H),
3.66 (s, AO¼¼COCH3, 3H), 2.56 (t, AO¼¼CCHCH2A, 1H), 2.41
(m, AO¼¼CCHCH2A, 1H), 2.03 (s, AO¼¼CCH3, 3H), 1.95
(m, AO¼¼CCHCH2A, 1H), 1.42 (t, AS¼¼COCH2CH3, 3H), 1.28
(d, AO¼¼CCHCH3, 3H). 13C NMR (CDCl3, 100 MHz): 209.9
(S¼¼CSCHA), 175.6 (CH3O¼¼O), 169.1 (CH3C¼¼O), 78.9
(S¼¼CSCHA), 70.2 (S¼¼COCH2A), 51.9 (O¼¼COCH3), 37.7
(O¼¼CCHCH2A), 36.2 (O¼¼CCHA), 20.8 (O¼¼CCH3), 17.2
(O¼¼CCHCH3), 13.6 (S¼¼COCH2CH3).
Xanthate 3 (Ethoxycarbonothioyl)sulfanyl tetraisopropyl
methylenediphosphonate
1H NMR (CDCl3, 400 MHz): d ¼ 1.28–1.32 (m, 24 H, CH-
(CH3)2), 1.40 (t, J ¼ 7 Hz, 3 H, CH2ACH3), 4.62 (t, J ¼ 21.7
Hz, 1 H, CH-P), 4.62 (q, J ¼ 7 Hz, 2 H, CH2ACH3), 4.73–4.84
(m, 4 H, CH-(CH3)2). 31P NMR (CDCl3, 162 MHz): d ¼ 14.21.
13C NMR (CDCl3, 100 MHz): d ¼ 13.69 (C(S)OCH2CH3),
23.52–24.24 (m, POCH(CH3)2), 43.21 (t, J ¼ 138.5 Hz, CH-P),
71.47 (C(S)OCH2CH3), 72.45–72.77 (m, POCH(CH3)2), 210.34
(C¼¼S).
RAFT/MADIX Polymerization of VAc
Bulk polymerization of VAc was performed using 2,20-azoiso-
butyronitrile (AIBN) as the initiator and the CTAs (given in
Table 1 and described in the synthesis section). VAc (Sigma
Aldrich, 99%) was purified by passing over a column of
basic aluminum oxide.
Xanthate 4 (Isopropoxycarbonothioyl)sulfanyl
tetraisopropyl methylenediphosphonate
A stock solution containing VAc, a CTA and AIBN ([AIBN]/
[CTA] ¼ 0.05/1) was prepared. Five samples of the stock so-
lution were transferred to individual Schlenk tubes of 6 mL,
which were thoroughly deoxygenated by freeze–pump–thaw
cycles. The tubes were then placed in a constant tempera-
ture oil bath at 70ꢀC, and a tube was removed at regular
time intervals. The reactions were stopped by cooling the so-
lution in liquid nitrogen. Final conversions were measured
1H NMR (CDCl3, 400 MHz): d ¼ 1.23–1.28 (m, 30 H, CH-
(CH3)2), 4.59 (t, J ¼ 21.2 Hz, 1 H, CH-P), 4.68–4.79 (m, 4H,
CH-(CH3)2). 31P NMR (CDCl3, 162 MHz): d ¼ 14.28. 13C NMR
(CDCl3, 100 MHz): d ¼ 21.04 (C(S)OCH(CH3)2), 23.37–24.14
(m, POCH(CH3)2), 42.74 (t, J ¼ 137 Hz, CH-P), 72.35–72.73
(m, POCH(CH3)2), 79.84 (C(S)OCH(CH3)2), 210.80 (C¼¼S).
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by 1H NMR and the molecular weight Mn and the PDI were
determined by GPC.
15 Salz, U.; Zimmermann, J.; Zeuner, F.; Moszner, N. J. Adhes.
Dent. 2005, 7, 107–116.
16 Zeuner, F.; Moszner, N.; Drache, M.; Rheinberger, V. Phos-
phrus Sulfur Silicon Relat. Elements 2002, 177, 2263.
CONCLUSIONS
17 Zeuner, F.; Moszner, N.; Volkel, T.; Vogel, K.; Rheinberger,
V. Phosphorus Sulfur Silicon Relat. Elements 1999, 144–146,
133–136.
New phosphonate/bisphosphonate-containing xanthates were
efficiently synthesized and used as CTAs for the RAFT/MADIX
polymerization of VAc. We have shown that the rate of VAc
polymerization is not influenced by the phosphonate moieties.
Indeed, similar polymerization behavior was observed with
VAc polymerizations mediated either by phosphonate-contain-
ing xanthates or by (methyl ethoxycarbonothioyl) sulfanyl ace-
tate, that is, without any phosphonate group. Thus the same
induction period of about 30 min was obtained for each xan-
thate. The same conclusion can be drawn about the control of
polymerization, as a linear evolution of Mw with monomer
conversion was observed whatever the xanthate CTA. Further-
more, PDIs values remained lower than 1.4 up to 70–80%.
These low-PDI values were attributed to a fast xanthate inter-
chain exchange, characterized by a Cex value of about 25, with
respect to the use of Rhodixan A1/VAc adduct in the RAFT/
MADIX polymerization of VAc. Finally, the end-group analysis
by Maldi-Tof revealed efficient phosphonate/bisphosphonate
chain-end functionalization of PVAc, that is, most of PVAc
chains contain acetophosphonate moiety in a-position. These
phosphonate end-capped PVAc may have great potential appli-
cations especially for water treatments after been hydrolyzed.
This will be the subject of a forthcoming article.
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