Preparation of unsaturated polyesters using boric acid as mild catalyst and their sulfonated derivatives as new family of degradable polymer surfactants

Article abstract of DOI:10.1016/j.polymer.2010.08.066

Boric acid-pyridine mixture is presented as mild catalyst for polycondensation of semi-esters of ethylene glycol, in situ-generated by " cyclic anhydride-diol" reaction scheme from maleic, succinic and phthalic anhydrides. This catalyst system was demonstrated to give colorless polyesters in low molecular weights (Mn: 1650-1950 Da) within 4 h at 130 °C ¹H NMR spectra of the polyesters derived from maleic anhydride revealed significant isomerization of maleate groups to fumarate units (～80 %) during the polyesterification. Maleate and fumarate double bonds of the unsaturated polyesters (USP) were demonstrated to add bisulfite ions quantitatively to give sulfonated polyesters. The resulting sulfonated polyesters with 50% and 70% succinate units exhibited relatively narrow size spherical and ellipsoidal micelles in aqueous solutions, as inferred from surface tension, DLS and ESEM measurements. The results showed that, this procedure allows preparing a new family of polymer surfactants with tunable hydrophilicity and degradable polyester backbones.

Full text of DOI:10.1016/j.polymer.2010.08.066

Polymer 51 (2010) 5044e5050
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Polymer
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Preparation of unsaturated polyesters using boric acid as mild catalyst and their
sulfonated derivatives as new family of degradable polymer surfactants
,
Neslihan Alemdar a, A. Tuncer Erciyes a, Niyazi Bicak b
*
a Istanbul Technical University, Chemical Eng. Dept. Maslak, 34469 Istanbul, Turkey
b Istanbul Technical University, Dept. of Chemistry, Maslak, 34469 Istanbul, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
Boric acid-pyridine mixture is presented as mild catalyst for polycondensation of semi-esters of ethylene
glycol, in situ-generated by “cyclic anhydrideediol” reaction scheme from maleic, succinic and phthalic
anhydrides. This catalyst system was demonstrated to give colorless polyesters in low molecular weights
(Mn: 1650e1950 Da) within 4 h at 130 ꢀC 1H NMR spectra of the polyesters derived from maleic
anhydride revealed significant isomerization of maleate groups to fumarate units (e80 %) during the
polyesterification. Maleate and fumarate double bonds of the unsaturated polyesters (USP) were
demonstrated to add bisulfite ions quantitatively to give sulfonated polyesters. The resulting sulfonated
polyesters with 50% and 70% succinate units exhibited relatively narrow size spherical and ellipsoidal
micelles in aqueous solutions, as inferred from surface tension, DLS and ESEM measurements. The results
showed that, this procedure allows preparing a new family of polymer surfactants with tunable
hydrophilicity and degradable polyester backbones.
Received 17 March 2010
Received in revised form
26 August 2010
Accepted 29 August 2010
Available online 6 September 2010
Keywords:
Unsaturated polyester
Polymeric surfactant
Amphiphilic polymer
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
and yield polyesters with high clarities, relatively high cost of
the germanium metal deters its extensive use. One important
Low molecular weight unsaturated polyesters (USP) (i.e.
1800e2500 Da) constituting with maleate/fumarate segments in
the backbone are versatile family of thermosetting materials having
extensive use in glass-fiber reinforcement etc. Solutions of the USP
in suitable vinyl monomers such as styrene are under marketing to
produce concrete-like polymer composites with fiber-glass [1].
Characteristics of the USP can be tuned by proper choice of the
diacid or diol components in the esterification formulations. In
most formulations, the principal diol, propylene glycol is partially
replaced with diethylene glycol to impart cracking resistivity. To
enhance thermal endurance and chemical resistance, isophthalic
acid is preferred as the acid component.
In the commercial polyesterification processes, well-known
acid catalysts such as H2SO4 and p-toluene sulfonic acid (PTSA)
have been replaced with antimony and titanium based catalysts,
to avoid their dehydrating effects yielding coloration. Titanium-
and tin-containing catalyst systems show high efficiency, but
may cause to coloration of the polyester product in longer
reaction periods [2]. Although germanium metal powder has
been demonstrated to reduce formation of cyclic oligomers [3]
aspect of the polyesterification with maleic anhydride is mal-
eateefumarate isomerization, which is useful to accelerate
hardening with styrene. Such isomerization occurs at 220 ꢀC
and facilitated by using catalysts, such as piperidine and mor-
pholine [4].
In the present work, boric acid is presented as a mild and
convenient catalyst for preparing colorless USPs in relatively short
reaction times using maleic anhydride as precursor for the unsat-
urated segments. The catalytic effect of boric acid was studied for
polycondensation of the hydroxyethyl esters generated from cyclic
anhydrides; namely maleic, succinic and phthalic anhydrides in
various time-temperature conditions. This procedure was also
employed for preparing unsaturated copolyesters using appro-
priate maleateesuccinate and maleateephthalate combinations.
The resulting unsaturated polyesters were sulfonated by action of
sodium hydrogen sulphite to give amphiphilic polyesters with
interesting solution behaviors. To our best, there appear no reports
in the literature, dealing with sulfonation of USPs and this paper
would be the first report on the subject.
In the study, conditions of the polyesterification, maleatee
fumarate isomerization and the sulfonation yields were discussed
based on 1H NMR, FT-IR spectra, and GPC and chemical analyses. The
surfactant behaviors of the sulfonated polymers were investigated by
surface tension, UV analyses.
* Corresponding author. Tel.: þ90 212 285 3221; fax: þ90 212 285 6386.
E-mail address: bicak@itu.edu.tr (N. Bicak).
0032-3861/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2010.08.066

N. Alemdar et al. / Polymer 51 (2010) 5044e5050
5045
2. Experimental
solution. The carboxyl end group content (in terms of mmol per
gram) was calculated from;
2.1. Materials and methods
a ¼ 5 ꢂ 0:103 ꢁ 0:1x=0:8
Where, x is the titer in mL.
Boric acid (E. Merck), Phthalic anhydride (PHA) (E. Merck),
maleic anhydride (MA) (Aldrich), succinic anhydride (SA) (Aldrich)
and pyridine (Fluka) were used without any further purification.
1H NMR spectra of the polymers were obtained by a Bruker
250 MHz NMR spectrometer, using CDCl3 and D2O as solvent for the
polyesters and their sulfonated derivatives respectively. FT-IR
spectra were recorded on a Perkin Elmer FT-IR Spectrum One B
spectrometer. UV spectra and transparencies were obtained using
Shimadzu UV 1240 model spectrometer. Gel Permeation Chroma-
tography (GPC) traces of the polyester samples were taken in
tetrahydrofuran (THF) with a flow rate of 0.3 mL/min using Agillant
1100 series instrument consisting of a pump, a refractive index-
detector and Waters Styrogel (HR4, HR3, HR2) columns. Poly-
styrene was used as standard. Critical micelle concentrations (CMC)
of the sulfonated polymers solutions were assigned by Young/
Laplace surface tension method using KSV’s CAM 200 surface ten-
sionmeter, at 20 ꢀC. The micelle sizes and size distributions in the
sulfonated polymer solutions were determined by dynamical light
scattering (DLS) method, using a Brookhaven 90 Zeta Plus Particle
Sizing Instrument. Shapes and sizes of the micelles were assigned
by Environmental scanning electron microscopy (ESEM) technique,
using Philips e FEI XL30, ESEM-FEG instrument operating at
5.00 kV in STEM mode. In these measurements concentrations of
aqueous polymer solutions were chosen slightly higher than their
CMCs (4.2 and 3.1 gLꢁ1 for the sulfonated polyesters with 50% and
70% SA contents respectively).
2.4. Sulfonation of the unsaturated polyesters with sodium bisulfite
The USP sample (2 g) was dissolved in ethylene glycol mono-
methyl ether (15 mL). This solution was mixed with 15 mL NaHSO3
solution (15%) and heated at 70 ꢀC in a 100 mL volume of flask
under reflux condenser. The mixture turned to be clear solution
within 2 h. The reaction was continued for 24 h. The resulting
solution was evaporated to dryness and the residue was dissolved
in 15 mL ethylene glycol monomethyl ether and filtered. The
sulfonated polymer was precipitated in 50 mL petroleum ether,
filtered and dried under a vacuum (50 ꢀC for 24 h). The resulting
polymers were soluble in water, ethanol and DMF. Extents of the
sulfonation reactions were assigned by 1H NMR spectra of the
polymers in D2O.
3. Results and discussion
3.1. Polyesterification using boric acid as mild catalyst
The catalytic effect of boric acid was studied in poly-
condensation of hydroxy carboxylic acids in situ-generated by
action of ethylene glycol on maleic, succinic and phthalic anhy-
drides. The reactions were carried out in one-pot using a typical
polyesterification set up in which extents of the polycondensations
were followed simply by monitoring volume of the water azeo-
tropicaly removed with toluene at 130 ꢀC. The reaction with cata-
lytic amounts of boric acid, however, was very slow at this
temperature. The esterification yield of the succinic acid semiester
was around 70% within 8 h as inferred from volume of the evolved
water.
Experiments showed that, addition of few milliliters of pyridine
accelerates the reaction considerably, so that polyesterification is
completed within 4 h at 130 ꢀC. Therefore, the reactions were
conducted in the presence of pyridine as cocatalyst. Overall scheme
of the polyesterification is in situ generation of hydroxy carboxylic
acids and their polycondensation using a boric acid-pyridine cata-
lyst as depicted in Scheme 1.
Catalytic effect of boric acid must be due to easy formation of
boron ester with the hydroxy groups of semi-esters of the dibasic
acids. The boron ester intermediate undergoes to acidolysis with
the free carboxyl group to form polyester. This acidolysis reaction is
very slow in the absence of pyridine. Role of the pyridine is to
dissociate the carboxyl group in the organic medium and proton of
the pyridinium cation attacks to the boron-oxygen bond to
generate carbocation on the alkyl fragment. Therefore, pyridine
seems to be essential cocatalyst to speed up of the poly-
esterification. Similar ionizing effect of pyridine on carboxylic acids
has been observed in direct esterification with alcohols [5]. The
same effect of pyridine is likely to occur in acidolysis of alkyl
borates. Simplified catalysis mechanism of the boric acid-pyridine
couple is depicted in Scheme 2.
2.2. Polyesterification of monohydroxyethyl esters of diacids using
boric acid catalyst
The polyesterifications of ethylene glycol (diol component) with
cyclic anhydrides were carried out in two steps. The reactions were
performed in a single reaction vessel in which monohydroxyethyl
esters of the diacids were formed first, by action of monoethylene
glycol on the cyclic anhydrides; MA, SA and PHA. The
u-hydroxy
acids generated were then, polycondensed in the presence of boric
acid-pyridine mixture, in the second step. A typical procedure is as
follows: To a 250 mL volume of flat bottom flask, there was added
18.6 g (0.3 mol) monoethylene glycol, 29.4 g (0.3 mol) MA and
50 mL toluene. The flask was equipped with a DeaneStark trap and
a reflux condenser and heated to 100 ꢀC for 30 min to form
monoester of maleic acid. To the cooled solution there was added
0.5 g H3BO3 and 5 mL pyridine and the mixture was heated at
130 ꢀC and kept constant at this temperature until water evolution
was ceased (ca. 4 h). Then, toluene was distilled off and the reaction
mixture was poured into 200 mL of cold NaHCO3 solution (3%). The
silky white polymer was separated by decanting the water phase.
The polymer was dissolved in 2-methoxyethanol (30 mL) and
reprecipitated in 200 mL NaCl solution (10%). White polymer was
dried at 50 ꢀC for 24 h under vacuum. The yield was 38 g (89.1%).
The same procedure was employed to produce the polyesters
and copolyesters constituting with succinate and phthalate
segments.
2.3. Determination of the carboxyl end groups
In order to prove this assumption, we carried out additional
experiment in which tributyl borate was reacted with an equivalent
amount of propanoic acid at 130 ꢀC for 8 h. The reaction mixture
was shaken with sodium carbonate solution and the organic layer
constituting with butyl propionate and butanol was separated.
Extent of the esterification was estimated by 1H NMR spectrum of
the mixture. An integral ratio of the CH2eO proton signal of the
One gram of the polyester sample was dissolved in 10 mL
2-methoxyethanol. To this solution, there was added 5 mL of
ethanolic KOH solution (0.103 M). The mixture was shaken and
poured into 35 mL of distilled water. The polyester precipitated was
filtered and 40 mL of the filtrate was titrated with 0.1 M HCl

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N. Alemdar et al. / Polymer 51 (2010) 5044e5050
Scheme 1. Polyesterification of the monohydroxyethyl esters of maleic, succinic and phthalic acids with boric acid as mild catalyst.
ester at 3.8 ppm to that of CH2eOH group signal of butanol at
3.5 ppm, revealed only 13% conversion. The repeated reaction in the
presence of pyridine yielded nearly quantitative conversion,
implying the deprotonating effect of pyridine.
The polycondensation of 2-hydroxyethyl esters derived from
maleic, succinic and phthalic anhydrides in the presence of a boric
acid-pyridine catalyst yielded colorless polyesters in low molecular
weights (Mn: 1650e1950) within 4 h (Table 1) as inferred from the
Scheme 2. Possible mechanism of boric acidepyridine catalysis in the esterification with carboxylic acids.

N. Alemdar et al. / Polymer 51 (2010) 5044e5050
5047
d
Table 1
Characteristics of the polymers obtained by polycondensation of
u-hydroxy carboxylic acids using boric acid catalyst.
a
u
eHydroxy acid
Polyester
React. time
Yield b (%)
Molecular
weight
eCOOH end group content
(mmolgꢁ1
c
)
Mn
Mw
HES
HEP
Poly(ethylene succinate)
Poly (ethylene phthalate)
Poly(ethylene maleate-co-ethylene fumarate)
Poly(ethylene succinate-co-ethylene
maleate-co-ethylene fumarate)
4 h
4 h
4 h
4 h
91.0
92.2
89.1
88.7
1800
1950
1650
1750
2750
2950
2800
2400
1.09 ꢃ 0.02
ND
HEM
HES þ HEM (1:1)
1.11 ꢃ 0.02
1.06 ꢃ 0.02
HEM þ HEP (1:1)
Poly(ethylene phthalate-co-ethylene
maleate-co-ethylene fumarate)
4 h
93.7
1950
3100
ND
a
The abbreviations; HES: 2-hydroxyethyl succinate, HEP: 2-hydroxyethyl phthalate, HEM: 2-hydroxyethyl maleate.
Practical yields.
By GPC.
b
c
d
ND: Not determined.
GPC traces. Extension of the reaction periods, however, did not
the maleate and fumarate double bonds at 6.4 and 6.9 ppm
respectively. Integral ratio of the two peaks implies about 80% of
fumarate segment in the polymer.
change the molecular weights. This was attributed to slight change
in alcohol to carboxylic acid ratio by evaporation traces amounts of
ethylene glycol during the process at 130 ꢀC.
Two weak signals at 5.85e6.15 ppm (labeled by asterisks)
represent protons of ]CHeCOO moieties associated with maleic
and fumaric acid end groups. Since optimal temperature of mal-
eateefumarate isomerization is 200 ꢀC, eighty percent of the
isomerization seems to be reasonably high at this temperature.
However, considering with accelerating effect of amines such as
piperidine and morpholine [7], this isomerization is not unexpected
and might happen by action of pyridine present in the reaction
medium. As a result polymerization of 2-hydroxyethyl maleate
yields fumarate rich (80%) unsaturated polyester, poly (ethylene
maleate-co-ethylene fumarate), in the conditions studied.
Determination of the end groups of the polymers by titration
revealed 1.06e1.11 mmol gꢁ1 of carboxylic acids, which are
almost double comparing with the theoretical values. By
assuming the presence of one carboxyl unit per chain, an average
1650 Da of molecular weight corresponds to 0.6 mmol carboxyl
end group per gram of the maleate polyester. Comparing with
1.20 mmol of theoretical carboxyl content, 1.11 mmol gꢁ1 found
for the polyester derived from MA implies that almost 90% of the
polyester chains bear carboxyl groups in both ends. The
remaining 10% carries one carboxyl end group per chain. The end
group titration of the other polyesters gave similar results as
given in Table 1. Those results confirm the assumption of
ethylene glycol loss, which is responsible for the low molecular
weights in the polycondensation process. This was also proven by
a separate experiment in which the polycondensation with SA
was repeated by using less volatile diethylene glycol as diol
component. The number average molecular weight attained at
the same period (4 h) was 4600.
3.2. Sulfonation of the polyesters
In this part of the work, addition of sodium hydrogen sulphite to
ethylenic double bonds of the unsaturated polyesters was studied.
The reaction with slightly excess of sodium hydrogen sulphite in
2-methoxyethanolewater mixture resulted in quantitative sulfo-
nation of the maleate and fumarate double bonds (Scheme 3).
Chemistry of bisulfite addition to ethylenic double bonds is well
documented in the literature [8]. The bisulfite addition to mono and
dialkyl esters of maleic acid is common method to produce
Since molecular weights of the polyester are in desired ranges
well suited with the classical hardening formulations, we did not
attempt to increase the molecular weights any further. Apparently,
the boric acid-pyridine acts as a mild catalyst for preparing colorless
polyesters within short times, which are advantages of this catalyst
system over the conventional esterification catalysts. Avoidance of
the color formation in this process must be due to high thermal
decomposition temperatures of the boron esters (>300 ꢀC) [6].
1H NMR spectra of the polymers confirm the polyester struc-
tures. Thus, in the 1H NMR spectrum of the polymer (see
supplementary data) obtained from succinic anhydride; the singlet
at 4.3 ppm in is associated with CH2 protons of the ethylene bridge.
The protons of succinic acid component represent another singlet
at 2.7 ppm. A similar pattern is observed for the case of poly
(ethylene phthalate) (see supplementary data). In this spectrum,
typical aromatic proton signals appear in 7.3e7.8 ppm and the
multiplet centered at 4.3 ppm is due to protons of the ethylene
bridge. The weak signal at 3.8 ppm is due to CH2OH end groups of
this polymer. An integral ratio of the last two peaks is around 1/18,
which is consistent with the molecular weight of the polymer (Mn:
1950). Although such a consistency of GPC data with NMR is
somewhat unexpected for the polyesters, this might be due to low
molecular weight of the polymer.
1H NMR spectrum of the polyester derived from maleic anhy-
dride (Fig. 1) exhibits two different proton signals associated with
Fig. 1. 1H NMR spectrum of the polymer, poly(ethylene maleate)2-co-poly(ethylene
fumarate)9 (Mn:1650) obtained by boric acid catalyzed polycondensation of
2-hydroxyethyl maleate in the presence of pyridine.

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N. Alemdar et al. / Polymer 51 (2010) 5044e5050
Similar pattern is observed in 1H NMR spectrum of the
sulfonated maleate-succinate copolyester (see supplementary
data) in which the signals above 5 ppm disappear and typical
proton signals of succinate group appear in 2.4e2.7 ppm range.
Sulfonation of the polyester derived from MA is also evidenced
by FT-IR spectra (see supplementary data). Thus, characteristic
carbonyl band and C]C stretching vibration band of the maleate
and fumarate segments appears at 1720 cmꢁ1 and at 1650 cmꢁ1
respectively. In the FT-IR spectrum of the sulfonated product the
carbonyl band slightly shifts to 1730 cmꢁ1.Disappearance of the
double bond vibration at 1650 cmꢁ1 is not clearly observable due to
new carbonyl band emerged in the same region, 1630e1650 cmꢁ1
.
This band is present also in the FT-IR spectrum of commercial
dioctyl sulfosuccinate (AOT) [11] that is a low molecular weight
analogue of the sulfonated polymer and can be attributed to
stretching vibration of the carbonyl group adjacent to the sulfonate
group. Lower frequency of this band must be due to increased
enolization behavior of C]O group. This polymer displays also
asymmetric vibration band of S]O at 1180 cmꢁ1 and a broad OeH
Scheme 3. Sulfonation of the unsaturated polyester, poly (ethylene maleate/fumarate).
corresponding sulfonate derivatives, e.g., dioctyl sulfosuccinate
(also known as Aerosil OT or AOT) having extensive use in textile
industry and in paint formulations [9].
stretching vibration band around 3300 cmꢁ1
.
To examine surfactant behavior of the sulfonated polymer
samples, their critical micelle concentrations (CMC) were measured
by surface tension method. Fig. 3 shows surface tensions of the
polymer surfactants as a function of concentration. It is seen that,
the sulfonated polymer with 50% SA content exhibits significant
change in surface tension around 3.4 g per liter concentration
which is assigned to its CMC (Table 2). Similar estimation for the
polymer with 70% SA gives a CMC of about 2.9 g per liter.
Micelle forming behaviors of the sulfonated polyesters were
investigated by DLS and ESEM techniques. In these experiments,
the polymer concentrations were chosen slightly higher than those
of their CMC’s (4.2 and 3.1 gLꢁ1 for 50% and 70% SA contents
respectively). DLS trace of the polymer with 50% SA content (Fig. 4)
shows an average particle diameter of 194.5 nm and relatively low
polydispersity (0.323) as inferred from the relevant histogram
(Fig. 4). ESEM image of this solution (Fig. 5) represents spherical
micelles with nearly equal sizes. These results are in good agree-
ment with DLS data.
However, sulfonate derivatives of polymeric maleates have not
been reported so far. Synthesis of sulfonated polyesters was
considered to be interestingduetodegradable natureof the polymer
backbone and possible “Gemini surfactant” effect of the multiple
sulfonate groups. Sulfonation of the USP in this work was carried out
with sodium hydrogen sulphite in 2-methoxyethanolewater
mixture (1:1). The polyesters derived from MA, MAeSA (1/1 mol/
mol) and MAeSA (3/7 mol/mol) mixtures were sulfonated by this
procedure. Sulfonation of the maleateephthalate copolyester was
not studied, owing to its hydrolytic instability in aqueous medium
[10]. Interestingly, the sulfonated polyesters are soluble in broad
range of polar organic solvents including water, DMF and NMP or in
their mixtures depending on the succinate content.
Those solution behaviors revealed potential use of these mate-
rials as emulsifying, stabilizing or solubilizing agents in o/w or w/o
systems.
1H NMR spectrum of the sulfonation product obtained by
bisulfite addition of poly (ethylene maleate/fumarate) is given as
a representative example in Fig. 2. It is clearly seen that proton
signals of maleate and fumarate double bonds at 6.4 and 6.9 ppm
disappear completely after the bisulfite addition. This result indi-
cates quantitative sulfonation of maleate and fumarate double
bonds at this temperature. Protons of the ethylene bridge in the
sulfonated polymer exhibit two separate peaks at 4.3and 3.8 ppm
for the CH2 groups. New peaks emerging in 3.6e3.3 ppm range are
due to CH and CH2 protons of the sulfosuccinate segments.
Significantly, larger average particle size (538.6 nm) and a wider
polydispersity (0.343) are observed in DLS picture of the polyester
with 70% SA content (Fig. 6a and b).
Fig. 2. 1H NMR spectrum of the sulfonated polyester derived from 2-hydroxyethyl
Fig. 3. Surface tension-surfactant concentration plot for the sulfonated polymer with
maleate (in D2O).
50% SA content (-), with 70% SA content ( ).
;

N. Alemdar et al. / Polymer 51 (2010) 5044e5050
5049
Table 2
Structural and solution characteristics of the sulfonated polyesters.
Unsaturated polyester
Succinate
Content mol %
Sulfanation
Degree a
CMC b
(g/L)
Averagec Micelle
size
Solubility
Poly(ethylene maleate-co-ethylene fumarate)
Poly(ethylene succinate-co-ethylene
maleate-co-ethylene fumarate)
e
100%
100%
e
e
Water, DMF, DMSO
Watereacetone (1:1),
WatereTHF (1:1)
50%
3.4
194.9 nm
Poly(ethylene succinate-co-ethylene
maleate-co-ethylene fumarate)
70%
100%
2.9
538.6 nm
WatereDMF(1:1) DMSO
a
Based on 1H NMR spectra.
Critical Micelle Concentration by surface tension Measurements.
By DLS.
b
c
Fig. 4. DLS trace of the aqueous solution of the sulfonated polymer with 50% SA (a) and histogram of its hydrodynamic diameter (b) (Concentration: 4.2 gLꢁ1).
Fig. 5. Representative ESEM micrographs of the micelles taken in the solution of sulfonated polymer with 50% SA content (4.2 gLꢁ1) (a) and with 70% SA content (3.1 gLꢁ1) (b). The
images were taken by the samples drop cast from aqueous solutions, without staining.
Fig. 6. DLS trace of the aqueous solution of the sulfonated polymer with 70% SA (a) and histogram of its hydrodynamic diameter (b) (Concentration: 3.1 gLꢁ1).
Apparently, increasingSAcontentof the polymerfrom50%to70%
increases the average micelle diameter by a factor of 2.5, in accor-
dance with its greater hydrophobicity. However, mostly ellipsoidal
micelles are seen in the ESEM image of this solution (Fig. 5). Overall
results of DLS and ESEM measurements imply amphiphilicity and
micellar behavior of the sulfonated polymer samples.
It is important to note that, sulfonated derivative of the poly-
ester constituting only with maleate segments was hydrophilic and
its aqueous solution did not show any sign of micelle formation.
4. Conclusion
Polyesterification of the hydroxy carboxylic acids, in situ-
generated from cyclic anhydrides, MA and SA proceeds with a boric
acidepyridine catalyst to give colorless oligoesters. Comparing
with 8e25 h of reaction periods for the conventional poly-
esterification process, short reaction time of the process (4 h) is
helpful to avoid coloration and to suppress branching or cross-
linking via addition of the hydroxy groups to maleate double bonds

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N. Alemdar et al. / Polymer 51 (2010) 5044e5050
as a side reaction. The USPs easily adds sodium bisulfite to give
sulfonated derivatives having good solubilities in many solvents.
Since the maleate ratio of the copolyester is adjustable parameter,
this procedure allows preparing degradable polymer surfactants
with desired hydrophilicities.
References
[1] Sahli A, Granger R, Vergnaud JM. Eur Polym J 1995;31:419e24.
[2] Siling MI, Laricheva TN. Russ Chem Rev 1996;65:279e86.
[3] Dulio V, Po R, Borelli R, Guarini A, Santini C. Angew Makromol Chem
1995;225:109e22.
[4] Schmidle CJ, Schmucker AE. US Patent 3,576,909, 1971.
[5] Ottera J. Esterification. New York: John-Wiley; 2003. p.30.
[6] Brandenberg W, Galat A. J Am Chem Soc 1950;72:3275e6.
[7] Parker EE. Ind Eng Chem 1966;58:53e8.
Acknowledgement
[8] Domsch A, Irrgang B. Surfactant science series, Vol. 56. New York: Marcel
Dekker; 1995. p.501.
[9] Lindner K. Tenside textilhilfsmittelwaschrohstoffe, Vol. 1. Stuttgart: Wissen-
schaftliche Verlagsgesellschaft; 1964. p.747.
Boron Research Institute of Turkish government supports this
work financially (BOREN-2006-12-C11>>17).
[10] Johnson KG, Yang LS. Preparation, properties and applications of unsaturated
polyesters. In: Scheirs J, Long TE, editors. modern polyesters: chemistry and
technology of polyesters and copolyesters. West Sussex, UK: John Wiley &
Sons; 2003. p. 703.
Appendix. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.polymer.2010.08.066.
[11] Deàk JC, Pang Y, Sechler TD, Wang Z, Dlott DD. Science 2004;306:473e6.