Synthesis and characterization of sulfonated telechelic bisphenol A polycarbonate ionomers

Article abstract of DOI:10.1016/j.reactfunctpolym.2011.07.002

Bisphenol A polycarbonate telechelic sulfonated ionomers have been prepared by melt polycondensation using bis(methyl salicyl) carbonate (BMSC), bisphenol A (BPA) and the sodium salt of sulfobenzoic acid phenylester (SBENa). Using an activated carbonate such as BMSC it is possible to decrease both reaction temperature and time respect to a standard polycondensation that use diphenylcarbonate (DPC) as carbonate precursor. Using the activated carbonate, ionomers with low Fries by-products and with good color have been obtained. The addition of SBENa permits the preparation of telechelic ionomers with ionic contents up to 3 mol%. All the properties of the telechelic ionomer obtained using BMSC are superior respect to those of the telechelic ionomers obtained using DPC. In particular, the ionomers prepared using BMSC are stable up to 400 °C and present higher glass transition temperature and storage modulus respect to standard PC.

Full text of DOI:10.1016/j.reactfunctpolym.2011.07.002

Reactive & Functional Polymers 71 (2011) 1001–1007
Contents lists available at ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Synthesis and characterization of sulfonated telechelic bisphenol
A polycarbonate ionomers
a
a
a
a
Martino Colonna a, , Corrado Berti , Enrico Binassi , Maurizio Fiorini , Simone Sullalti ,
⇑
Francesco Acquasanta a, Sreepadaraj Karanam b, Daniel J. Brunelle c
a Dipartimento di Ingegneria Civile, Ambientale e dei Materiali, Via Terracini 28, 40131 Bologna, Italy
b SABIC Innovative Plastics, Plasticslaan 1, 4600 AC Bergen op Zoom, The Netherlands
c General Electric Global Research, One Research Circle, Niskayuna, NY 12309, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Bisphenol A polycarbonate telechelic sulfonated ionomers have been prepared by melt polycondensation
using bis(methyl salicyl) carbonate (BMSC), bisphenol A (BPA) and the sodium salt of sulfobenzoic acid
phenylester (SBENa). Using an activated carbonate such as BMSC it is possible to decrease both reaction
temperature and time respect to a standard polycondensation that use diphenylcarbonate (DPC) as car-
bonate precursor. Using the activated carbonate, ionomers with low Fries by-products and with good
color have been obtained. The addition of SBENa permits the preparation of telechelic ionomers with
ionic contents up to 3 mol%. All the properties of the telechelic ionomer obtained using BMSC are superior
respect to those of the telechelic ionomers obtained using DPC. In particular, the ionomers prepared using
BMSC are stable up to 400 °C and present higher glass transition temperature and storage modulus
respect to standard PC.
Received 12 April 2011
Received in revised form 20 June 2011
Accepted 2 July 2011
Available online 13 July 2011
Keywords:
Bisphenol A polycarbonate
Telechelic ionomer
Bis(methyl salicyl) carbonate
Activated carbonate
Polycondensation
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
(polymers with ionic groups randomly distributed along the poly-
mer chain) give rise to a gel-like or cross-linked aggregation [1].
The presence of covalently bonded ionic groups along the poly-
mer chain produces a consistent modification on the physical and
rheological properties of polymers [1–4]. Indeed, ionomers (poly-
mers containing less than 10 mol% of ionic groups) have been
shown to exhibit considerably higher moduli and higher glass tran-
sition temperatures compared to those of their non-ionic analogues
[1]. Improvements in mechanical and thermal performance are
generally attributed to the formation of ionic aggregates, which
act as thermo-reversible cross-links [1] and effectively retard the
translational mobility of polymeric chains. The thermo-reversible
nature of ionic aggregation may address many other disadvantages
associated with covalently bonded high molecular weight poly-
mers, such as poor melt processability, high melt viscosity and
low thermal stability at typical processing conditions such as high
shear rate and temperature.
For this reason, telechelic ionomers having lower melt viscosities
and higher molecular weights than random ionomers can be pre-
pared [6]. We have reported [7,8] the synthesis of telechelic
poly(butylene terephthalate) (PBT) ionomers and a comparison
with PBT random ionomers. We have observed higher thermal
and hydrolytic stability and lower melt viscosity for telechelic
ionomers respect to random ionomers.
We have also reported [9,10] the positive effect of ionic groups
in PBT/montmorillonite nanocomposites. Indeed, nanocomposites
prepared with PBT telechelic ionomers present a better dispersion
of the organo-modified clay and better thermo-mechanical proper-
ties (higher heat distortion temperatures and modulus) respect to
the nanocomposite of non-ionic polymers.
On the basis of our work on polyester ionomers we have ex-
tended our studies to bisphenol A polycarbonates (PC). The pres-
ence of ionic groups should improve the clay dispersion in PC/
clay nanocomposites and should, in principle, also consistently
change the rheological properties of BPA polycarbonates. To the
best of our knowledge only one patent reports the synthesis of PC
telechelic sulfonated ionomers [11]. The authors report that PC
ionomers, prepared by melt and interfacial methods, present a
strong non-Newtonian melt rheology behavior along with in-
creased solvent and flame resistance. However, they do not present
any direct evidence of the insertion of ionic groups in the polymer
Telechelic ionomers are polymers with ionic groups selectively
located at the end of the polymer chains that provide the opportu-
nity for electrostatic interactions without a deleterious effect on
the symmetry of the repeating unit [5]. Moreover, the ionic aggre-
gations occur only at the end of the chain, giving rise to electro-
static chain extension. On the contrary, random ionomers
⇑
Corresponding author. Fax: +39 0512090322.
E-mail address: martino.colonna@unibo.it (M. Colonna).
1381-5148/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.reactfunctpolym.2011.07.002

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M. Colonna et al. / Reactive & Functional Polymers 71 (2011) 1001–1007
chain and no complete chemical characterization is provided.
Moreover, it is well known that ionic groups and sodium salts cat-
alyze degradation reaction in PC [12]. Therefore, high degradation
rates should be expected in the melt polycondensation synthesis
of ionomeric sulfonated PC due to the high reaction temperature
(280–300 °C) and long residence time required to achieve high
molecular weight polymers. The reason of the choice of positioning
the ionic groups selectively as end-groups is related to the high
melt viscosity of polycarbonate. The presence of ionic groups in-
creases the melt viscosity and therefore the elimination of the
low molecular product, necessary to increase molecular weight, be-
comes more difficult. It is well known that random ionomers give
rise to cross-link type aggregations while telechelic ionomers pro-
duce chain-extension type aggregations. Therefore, a consistently
higher melt viscosity is expected for random ionomers with respect
to telechelic ionomers with the same amount of ionic moieties.
Activated carbonates, such as bis(methyl salicyl) carbonate
(BMSC) can be used in order to decrease polymer degradation
[13,14]. The use of this more active carbonate allows a shorter
polycondensation process at lower temperatures (270 °C) [13,14].
Moreover, the equilibrium of the reaction between BPA and BMSC
is shifted toward the formation of the products (94%) and therefore
the reaction proceeds even without the continuous elimination of
the reaction products while using DPC the reaction equilibrium is
shifted towards the reagents and the continuous elimination of
phenol is necessary to reach high conversion and high molecular
weights [15]. For these reasons the use of BMSC must be preferred
when long reaction time and high temperature must be avoided in
order to decrease side reactions.
vacuum oven at 90 °C and characterized by 1H NMR analysis and
melting temperature (287 °C).
2.2.2. Preparation of sulfonated telechelic PC using BMSC
A round bottom wide-neck glass reactor (250 mL capacity) was
charged with bisphenol A (25.30 g; 110.8 mmol), SBENa (1.00 g;
3.32 mmol) and the catalyst water solution (a mixture of 2.22 Â
10À2 mmol tetramethylammonium hydroxide and 8.43 Â 10À5
mmol of NaOH in 0.1 mL of H2O).
The reactor was closed with a three-neck flat flange lid
equipped with a mechanical stirrer, a torque meter, a nitrogen inlet
and the system was then connected to a liquid nitrogen cooled
condenser. The reactor was purged three times with nitrogen and
immersed in a thermostated molten salt bath at 210 °C and the
stirrer switched on at 100 rpm after complete melting of the reac-
tants. After 90 min BMSC (36.95 g; 111.9 mmol) was carefully
added and dynamic vacuum was applied at 130 mbar for 10 min.
The temperature was then increased to 260 °C in 10 min and the
pressure decreased to 1 mbar. The reaction melt was very viscous
after 10 min from the application of dynamic vacuum and the stir-
ring was very difficult and slow in the last part of the polymeriza-
tion. After 30 min from the application of the vacuum, the very
viscous pale yellow and transparent melt was discharged from
the reactor.
2.2.3. Preparation of sulfonated telechelic PC using DPC
The reactor was filled with diphenyl carbonate (11.08 g,
0.52 mol) bisphenol A (11.25 g, 0.49 mol) and sodium phenyl 3-sul-
fobenzoate. The reactor was heated to 220 °C under a nitrogen
atmosphere. The catalyst (an aqueous mixture of 2.22 Â 10À2 mmol
tetramethylammonium hydroxide and 8.43 Â 10À5 mmol of NaOH
in 0.1 mL of H2O) was added to the stirred reaction solution. The
reaction pressure was then reduced at 30 mbar/min down to
30 mbar and then at 5 mbar/min until a final pressure of 0.2 mbar
was reached. The reaction temperature was increased to 280 °C
and maintained at that temperature for 2 h at full vacuum. The vis-
cous brown melt was then discharged from the reactor.
In this paper we report the first synthesis and characterization
of bisphenol A polycarbonate ionomers using activated carbonates
by a melt polycondensation process.
2. Experimental
2.1. Materials
Sodium 3-sulfobenzoic acid, diphenyl carbonate, sodium car-
bonate, bisphenol A, tetramethylammonium hydroxide, sodium
hydroxide (all from Aldrich Chemicals) were high purity products
and were not purified before use. Bis(methyl salicyl) carbonate
was a gift from SABIC-IP [13].
2.3. Physico-chemical characterization
1H NMR spectra were recorded with a Varian XL-400 spectrom-
eter (chemical shifts are downfield from TMS), using hot deuter-
ated DMSO as solvent. The spectra have been recorded just after
dissolution in order to avoid the precipitation of the polymer.
Gel permeation chromatography (GPC) analysis was performed
using chloroform as eluent (elution rate of 0.3 mL/min) on a HP
2.2. Synthesis
2.2.1. Preparation of phenyl 3-sulfobenzoate sodium salt (SBENa)
A 1 L, 3-neck flask equipped with thermometer, mechanical
stirrer and distillation head was filled with sodium 3-sulfobenzoic
acid (133.3 g; 0.67 mol), diphenyl carbonate (288.0 g; 1.34 mol)
and sodium carbonate (1.500 g; 14.0 mmol). The flask was placed
under a nitrogen atmosphere and heated with a heating mantle.
Once the diphenyl carbonate was melted the mechanical stirring
was started. When the temperature of the melt reached 300 °C
phenol started to distill. After about 30 min phenol distillation
stopped and the heat was removed. The dark melt solidified to a
yellow solid. After cooling the solid was removed from the flask
and dissolved in approximately 400 mL of water. The aqueous
solution was washed twice with 300 mL of methylene chloride
and then the water was removed by rotary evaporation to yield
the crude product. The solid was then suspended in ethanol and
warmed on a steam bath to form a solution. The solution was
hot filtered and then heated on the steam bath to evaporate the
solvent until the beginning of the crystallization. The solution
was cooled to room temperature and then put in a refrigerator at
about 5 °C. The product was collected by filtration and dried in a
1100 Series apparatus equipped with a PL Gel 5 l Mini-Mixed-C
column and a UV detector. Calibration was performed with polysty-
rene standards. Benzyltriethylammonium chloride (0.05 mol/L)
was also added in order to suppress ionic aggregations.
Differential scanning calorimetry (DSC) analysis was performed
using a Perkin Elmer DSC6. The instrument was calibrated with
high purity standards (indium and cyclohexane). Dry nitrogen
was used as purge gas. DSC heating and cooling rates were 20 °C/
min. All transitions have been measured after a heating to 270 °C
and cooling to room temperature in order to delete previous ther-
mal history.
The thermogravimetric analyses (TGA) were performed using a
Perkin Elmer TGA7 apparatus in N2 (gas flow: 40 mL/min) at 10 °C/
min heating rate, from 60 °C to 800 °C.
Dynamical mechanical thermal (DMTA) analyses were per-
formed with a Rheometrics dynamic mechanic thermal analyzer
DMTA 3E with a single cantilever testing geometry. Typical test
samples were bars that were compression molded at 260 °C. The
testing was done at a frequency of 3 Hz and temperature range
was from À50 °C to 200 °C at a rate of 3 °C/min.

M. Colonna et al. / Reactive & Functional Polymers 71 (2011) 1001–1007
1003
Melt rheologic properties were measured by a stress-controlled
Rheometric Scientific SR5 rheometer using a parallel plate geome-
try with a disc diameter of 25 mm. The frequency was varied from
0.1 rad/s to 500 rad/s. Typical test disk specimens were compres-
sion molded at 260 °C using a Carver press and a custom made mold.
and BPA can be followed by comparing the two peaks at d8.64
and 8.68 ppm ascribable to the reacted and unreacted sulfobenzoic
acid phenylester, respectively. After 90 min at 210 °C most of the
SBENa has already reacted. The 1H NMR analysis have been con-
ducted in deuterated DMSO since using this solvent it was possible
to obtain spectra with signals more separated and therefore easier
to integrate in order to measure the ionic content respect to the
use of CDCl3 as solvent.
3. Results and discussion
The 1H NMR spectrum of the crude product (Fig. 3) shows that
no unreacted SBENa is left and that no side-reaction take place
using BMSC as monomer. We have not observed any significant
evidence of the reaction of the methyl ester group of BMSC with
SBENa or BPA. Moreover, no singlet at d8.15 ppm due to Fries by
products is present [16]. On the contrary using DPC a consistent
amount of Fries products was present in the fraction soluble in
hot deuterated DMSO. In this case the final polymer was not com-
pletely soluble both in hot DMSO and in chloroform indicating that
part of the polymer has been cross-linked by side reactions such as
Fries rearrangements. Due to this not complete solubility we have
not measured the molecular weight of PC telechelic ionomers
made from DPC.
The TGA analysis (Fig. 4) shows that the 3 mol% telechelic iono-
mer prepared using BMSC is consistently more stable (30 °C) com-
pared to that prepared from DPC. Moreover, the telechelic PC from
DPC is consistently darker. The stronger degradation and side reac-
tions that occurs using DPC can be ascribed to the longer reaction
times and temperature needed for the synthesis without the acti-
vated carbonate.
The molecular weight, thermal properties and end-groups are
reported in Table 1. The amount of ionic end groups have been cal-
culated comparing the signal at 8.7 ppm (1H form the ionic end-
groups) with the integral of the signals between 7.4 and 7.1 ppm
(8H of BPA group). OH end groups have been calculated comparing
the signal at 6.6 ppm (2H of aromatic protons close to OH) with to-
tal BPA signals (7.4–7.1 ppm). For methyl salycilate end groups we
have compared the signal at 8.12 ppm (1H of methyl salycilate)
with total BPA signals (7.4–7.1 ppm). The molecular weight calcu-
lated by end-groups analysis (by 1H NMR) shows a good correla-
tion with ionic content since ionic groups act as chain stoppers
and therefore the molecular weight should decrease increasing
the ionic content. On the contrary, an opposite trend has been
found when molecular weight was measured by GPC in chloroform
as solvent. This behavior can be explained by the ionic aggregation
that produces polymer–polymer and polymer–column interac-
tions. In order to suppress ionic interactions, benzyltriethylammo-
nium chloride was added since it is reported in the literature [17]
The method reported in literature [11] for the melt polyconden-
sation synthesis of telechelic sulfonated PC consists in the addition
of the phenylester of sulfobenzoic acid sodium salt (SBENa) at the
beginning of the polycondensation between bisphenol A (BPA) and
diphenylcarbonate. However, when we performed this method we
obtained a consistent amount of degradation products obtaining a
dark yellow material not completely soluble in dichloromethane.
The main reason of this insolubility can be ascribed to the cross-
linking due to the formation of Fries rearrangement by-products
caused by the catalytic effect of the ionic groups towards side reac-
tions. Therefore, in order to decrease the amount of side-product
an activated carbonate (such as BMSC) must be used.
The one-pot reaction of BMSC, BPA and SBENa does not produce
telechelic ionomers since the reaction mixture remains opaque and
the SBENa can be mainly recovered unreacted at the end of the
polymerization process. In order to improve the reaction of BMSC
with BPA we have adopted an approach similar to that used for
telechelic PBT synthesis [8]. This method (Fig. 1) consists in pre-
reacting the sulfobenzoic acid derivative with the diol (in this case
BPA) in order to improve the solubility of the salt. Moreover, 1H
NMR analysis of samples taken during the first stage of polymeri-
zation shows that the reaction of BMSC and BPA is consistently fas-
ter than the reaction of SBENa with BPA. Therefore, after a few
minutes of reaction the amount of unreacted BPA drops consis-
tently thus decreasing the reaction rate with SBENa. The pre-stage
was conducted for 90 min at 210 °C. The 1H NMR analysis (Fig. 2)
shows the almost complete reaction of the SBENa with BPA. BMSC
was then added and the vacuum was slowly reduced to 130 mbar.
The temperature was then increased to 260 °C while the vacuum
decreased to 0.1 mbar. The reaction melt became very viscous in
a few minutes and the reaction was carried at full vacuum for addi-
tional 30–45 min. A pale yellow and completely transparent poly-
mer was obtained. The excess of BMSC used depends on the reactor
geometry. However, the stoichiometry can be easily balanced by
measuring by 1H NMR the amount of end groups deriving from
BPA or BMSC.
The 1H NMR spectra of samples taken during the pre-stage
(Fig. 2) show that the progress of the reaction between SBENa
Fig. 1. Polymerization scheme.

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M. Colonna et al. / Reactive & Functional Polymers 71 (2011) 1001–1007
Fig. 2. 1H NMR in d-DMSO of sample at different reaction time during pre-stage using BMSC as monomer.
Fig. 3. 1H NMR of the aromatic zone of telechelic ionomers made using BMSC and of the soluble part of that made from DPC in d-DMSO.

M. Colonna et al. / Reactive & Functional Polymers 71 (2011) 1001–1007
1005
Fig. 4. TGA analysis of telechelic PC made from BSMC and from DPC.
Table 1
Molecular weight, end-groups and thermal properties of sulfonated telechelic ionomers made using BMSC.
SBENa (mol%)a
GPC
Mw
1H NMR
DSC
Mn
Ionic end-groups (mol%)b
OH and methyl salycilate end groups (mol%)b
Mn
Tg (°C)
0
1
2
3
57,000
65,200
69,000
70,300
25,500
22,200
25,300
22,700
–
1.77
1.55
1.25
1.31
28,700
20,730
15,630
12,360
153
158
154
153
0.9
1.9
2.8
a
mol% respect to BPA units in the feed.
mol% respect to BPA units in PC samples.
b
that the addition of salts to the GPC solvent permits to suppress io-
nic interactions. However, no significant differences were observed
in Mw measured by GPC after the salt addition. Gel permeation
chromatography is not the appropriate method for the determina-
tion of molecular weight in ionic polymers since it is difficult to
completely suppress ionic aggregations that are responsible for
not reliable molecular weight values. For this reason, all correla-
tions between ionomers properties and molecular weight have
been performed just considering the molecular weight calculated
by end-group analysis.
DSC analysis shows that ionomers present a higher Tg respect to
non-ionic PC. However, there is no direct correlation between ionic
content and glass transition temperature since the higher Tg
(158 °C) has been observed for the 1 mol% telechelic ionomer. This
behavior can be ascribed to the fact that there are two variables
affecting Tg, the molecular weight and the ionic content. As
Fig. 5. TGA of telechelic PC made form BMSC.

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M. Colonna et al. / Reactive & Functional Polymers 71 (2011) 1001–1007
Fig. 6. Storage modulus of telechelic ionomers measured by DMTA.
Fig. 7. Complex melt viscosity (g⁄) analysis at 260 °C.
discussed previously, for telechelic ionomers the increase in ionic
content decreases the molecular weight and therefore the effect
of the lower molecular weight for ionomers counterbalance the ef-
fect of the ionic content on Tg and a maximum is reached for
1 mol% ionic content.
TGA analysis (Fig. 5) indicates that ionomers are less stable
compared to standard PC, nevertheless are stable up to 400 °C well
above the typical processing conditions of PC. DSC analysis showed
that no crystallinity was present in PC ionomers.
DMTA analysis (Fig. 6) shows that ionomers have higher moduli
above Tg respect to PC. However, also in this case no correlation be-
tween ionic groups content and storage modulus has been found.
Similar to what observed for the glass transition temperature, this
behavior can be connected to the presence of two concurrent ef-
fects: the modulus increases both with the ionic content and with
molecular weight. However, for telechelic ionomers, the increase of
the ionic content decreases the molecular weight since the ionic
groups act as chain stoppers. Therefore, the most consistent in-
crease in modulus can be observed with ionic content of 1 and
2 mol% while for 3 mol% of ionic end-groups almost no increase
in modulus can be observed due to the balance between ionic
groups effect and molecular weight decrease.
Melt viscosities of PC ionomers were measured in order to study
the effect of ionic aggregation on polymer chain mobility. Dynamic
frequency sweep tests at 260 °C (Fig. 7) reveals that all the iono-
mers have a higher complex viscosity and have a stronger non-
Newtonian behavior compared to standard PC. Again, the enhance-
ment in complex viscosity (g⁄) cannot be linearly related with the
ionic end-group content since the effect of ionic terminals on rhe-
ological properties is probably balanced by the lower Mn for iono-
mers with higher ionic content. For this reason complex viscosity
feels the simultaneous effect of ionic groups and molecular weight
and all a maximum is reached at lower ionic content (1 mol%).
4. Conclusions
PC sulfonated telechelic ionomers have been successfully pre-
pared by melt polycondensation using bis(methyl salicyl) carbon-
ate, BPA and the phenylester of sulfobenzoic acid sodium salt.

M. Colonna et al. / Reactive & Functional Polymers 71 (2011) 1001–1007
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