Synthesis and characterization of imidazolium telechelic poly(butylene terephthalate) for antimicrobial applications

Article abstract of DOI:10.1016/j.reactfunctpolym.2011.12.003

Poly(butylene terephthalate) ionomers with imidazolium groups selectively located as end-groups (telechelic) have been prepared by melt polycondensation adding a hydroxyl derivatized imidazolium salt at the beginning of the polymerization process. The des

Full text of DOI:10.1016/j.reactfunctpolym.2011.12.003

Reactive & Functional Polymers 72 (2012) 133–141
Contents lists available at SciVerse ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Synthesis and characterization of imidazolium telechelic poly(butylene
terephthalate) for antimicrobial applications
a
a
a
a
Martino Colonna a, , Corrado Berti , Enrico Binassi , Maurizio Fiorini , Simone Sullalti ,
Francesco Acquasanta a, Micaela Vannini a, Diana Di Gioia b, Irene Aloisio b, Sreepadaraj Karanam c,
Daniel J. Brunelle d
⇑
a Dipartimento di Ingegneria Civile, Ambientale e dei Materiali, Via Terracini 28, 40131 Bologna, Italy
b Dipartimento di Scienze e Tecnologie Agroambientali, viale Fanin 42, 40127 Bologna, Italy
c SABIC Innovative Plastics, Plasticslaan 1, 4600 AC Bergen op Zoom, Netherlands
d 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:
Received 14 October 2011
Received in revised form 28 November 2011
Accepted 4 December 2011
Available online 8 December 2011
Poly(butylene terephthalate) ionomers with imidazolium groups selectively located as end-groups
(telechelic) have been prepared by melt polycondensation adding a hydroxyl derivatized imidazolium
salt at the beginning of the polymerization process. The design of the chemical structure of the imidazo-
lium salt is of fundamental importance in order to achieve the synthesis of ionomers with good thermo-
mechanical properties. The final ionomers present high molecular weight, good color, transparency and
thermal stability. Imidazolium ionomers present good antimicrobial (AM) properties comparable with
those of commercial AM agents. The incorporation of the ionic groups in the polymer chain prevents their
migration during use and therefore the antimicrobial activity can be preserved for longer time.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Imidazolium salt
Telechelic
Ionomer
Polyester
Antimicrobial properties
1. Introduction
reason, in the last years, several research groups have tested the
use of antimicrobial agents covalently bonded to the polymer
Imidazolium salt derivatives have been used in the last few
years in several biological and material science applications. For
example, a recent review [1] reports that polyimidazoles can be
used as oxygen transport membranes [2] or as scaffold for biomi-
metic applications [3]. Imidazolium ionomers can also be used to
create polyelectrolyte brushes [4], coat metal nanoparticles [5]
and produce oriented liquid crystals [6]. Moreover, imidazolium
salts have proved to be very active as microbicidal agents [7,8].
The effect of substituents of the imidazolium moiety on the anti-
bacterial activity of imidazolium salts has been reported in the lit-
erature [8]. In particular, imidazolium salts bearing long alkyl
chains (with 15–18 methylene groups) present the stronger bacte-
ricidal properties [8].
Imidazolium derivatives have been used in most applications as
additives blended with the polymer matrix [7]. However, the use of
antimicrobial agents blended in a polymer matrix can give rise to
the migration towards the surface of the antibacterial agent and
therefore the antimicrobial activity decreases during the lifetime
of the polymer application such as fiber or molded article. For this
chain [9]. For example, Chen et al. [10] described the surface graft-
ing polymerization of N-vinyl-2-pyrrolidone onto poly(ethylene
terephthalate) by plasma pretreatment with silver nanoparticles.
Konagaya et al. [11] have reported the preparation of antibacterial
acrylic acid-grafted copolyesters with phosphonium salts. Cen et
al. [12] studied a surface functionalization technique for conferring
antibacterial properties to polymeric and cellulosic surfaces, using
a pyridinium salt grafted by copolymerization. Other researchers
have reported [13] the use of vinyl pyridine grafted with alkyl
chains. Other studies [14] pointed out that hexadecyl alkyl chains
bonded to diazobicyclooctane (DABCO) are active against bacteria.
The synthesis of polyaramides with pendant alkyl ammonium
groups that mimic peptide groups is also described in the literature
[15]. However, quaternary ammonium cations are not stable en-
ough to be incorporated in a terephthalate polyester chain since
they are subjected to degradation reactions at the normal synthesis
and processing conditions of such polyesters. On the contrary, imi-
dazolium cations have a consistently higher thermal stability. For
example, clays modified with imidazolium cations are stable at
temperature exceeding 300 °C while those modified with ammo-
nium salts start degrading below 240 °C [16]. It is important to
note that the counterion severely affects the thermal stability of
⇑
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.2011.12.003

134
M. Colonna et al. / Reactive & Functional Polymers 72 (2012) 133–141
imidazolium salts. It is reported in the literature [17] that tetra-
fluoroborate salts (BFꢀ4 ) and hexafluorophosphate salts (PFꢀ6 ) are
much more stable than chloride and bromide salts.
umn and a UV detector. Calibration was performed with polysty-
rene standards.
Calorimetric measurements have been performed using
a
Ionic groups can be inserted in the polymer chains selectively at
the chain ends (telechelic ionomers) or randomly distributed along
the polymer chain (random ionomers) [18–21]. The position of the
ionic groups strongly affects the polymer thermal, mechanical and
rheological properties.
Telechelic ionomers provide the opportunity for electrostatic
interactions without a deleterious effect on the symmetry of the
repeating unit [22]. Moreover, the ionic aggregation occurs only
at the ends of the chains, giving rise to an electrostatic chain exten-
sion while random ionomers give rise to a gel-like or cross linked
aggregation [18]. For this reason, lower melt viscosities and there-
fore high molecular weights can be obtained for telechelic iono-
mers with respect to random ionomers [23].
Perkin Elmer DSC6 instrument equipped with a liquid sub ambient
accessory and calibrated with high purity standards (indium and
cyclohexane). Dry nitrogen was used as purge gas. The heating
and cooling rate were 20 °C/min. All transitions have been mea-
sured after a heating scan to 250 °C and cooling down to room tem-
perature in order to delete previous thermal history.
The thermogravimetric analyses (TGA) were performed using a
Perkin Elmer TGA7 apparatus in nitrogen (gas flow: 40 mL minꢀ1
)
at 10 °C/min heating rate, from 25 °C to 800 °C.
DMTA analyses were performed with a Rheometrics dynamic
mechanic thermal analyzer DMTA 3E with a dual cantilever testing
geometry. Typical test samples were bars that were injection
molded at 275 °C using a Minimax Molder (Custom Scientific
The presence of ionic groups at the end of the polymer chain can
be useful for other important applications. For example, we have
recently reported the synthesis of PBT telechelic sulfonated iono-
mers [24] and their ability to consistently increase the heat distor-
tion temperature of PBT nanocomposites since the electrostatic
interaction with the surface of the clay platelets gives rise to a bet-
ter dispersion of the clay and to an improved adhesion between the
clay and the polymer [25]. Imidazolium cations should in principle
provide a better adhesion to the clay surface (negatively charged)
compared to anionic ionomers such as sulfonated ionomers.
For all the reasons reported above the preparation of tere-
phthalate polyesters with potential antibacterial properties, good
thermal stability and mechanical properties looks very interesting.
The imidazolium ionomers can be prepared by addition of hydro-
xyl functionalized imidazolium salts during the standard polymer-
ization process of terephthalate polyesters. In this paper we report
the synthesis of the OH derivatized imidazolium monomers as well
as the first synthesis and the characterization of telechelic imi-
dazolium polyester ionomers. We also report the study of the effect
of the different types of counterions and of the length of alkyl
chains on the thermal stability and on the polymerization process.
Moreover, the anti-microbial effectiveness of the synthesized poly-
mers was evaluated and compared to Triclosan, a widely used anti-
bacterial agent whose safety is, however, not yet fully elucidated.
Instruments) equipped with
a
rectangular mold (30 ꢁ 8 ꢁ
1.6 mm3). The testing was done at a frequency of 3 Hz and temper-
ature range was from ꢀ50 °C to 150 °C at a rate of 3 °C/min.
Inherent viscosities (IV) were measured at 25 °C with an
Ubbelhode viscosimeter using a 0.05 M solution of benzyltriethyl-
ammonium chloride in 1,1,2,2-tetrachloroethane/phenol 60/40 wt/
wt. The salt was used in order to suppress ionic aggregation be-
tween chains which can induce an overestimation of molecular
weight.
2.3. Antimicrobial properties
A Gram positive strain, Staphylococcus aureus ATCC 6538, and a
Gram negative strain, Escherichia coli ATCC 25645, were used to
evaluate the antimicrobial properties of the polymers. The speci-
mens employed were of the same type used for the DMTA analyses
(i.e. containing ionic end groups at 0.6, 1 and 2 mol% and Triclosan
at 0.6, 1 and 2 mol%) plus a control specimen not containing any
agents. Each strain was grown aerobically in Nutrient Broth (NB,
provided by Becton, Dickinson and Company, Maryland, USA) for
18 h at 37 °C. The culture thus obtained was centrifuged at
7000 rpm for 10 min, the pellet was washed in sterile saline
(8.5 g NaCl/L) and resuspended in saline in order to obtain a cell
suspension of 108 CFU mLꢀ1. An agar slurry solution was prepared
dissolving 0.3 g agar (Biolife Italia, Milan, Italy) in 100 mL saline;
the solution was autoclaved at 121 °C for 30 min, cooled at about
40 °C and inoculated with 1 mL of the prepared cell suspension.
The specimens were pre-wetted with sterile saline, placed into a
petri dish and 0.25 mL of inoculated agar slurry solution were pip-
ette onto the specimen. The cell layer was lower than 1 mm in
depth over the entire specimen surface. The slurry solution was al-
lowed to dry, and then the petri dishes containing the inoculated
specimens were placed on a capped box in which a 0.5 mm of
water was layered in order to avoid sample drying during incuba-
tion. Incubation was performed at room temperature for 24 h.
After incubation, the specimen was placed in a StomacherÒ Bag
(Seward, Worthing, United Kingdom) with 10 mL of saline, vigor-
ously shaken for 3 min in a Stomacher Bag apparatus to allow
the complete release of agar slurry from the sample. Serial dilu-
tions of the solution were performed, plated on Plate Count Agar
(Biolife) plates which were incubated for 48 h at room tempera-
ture. Each specimen was processed in triplicate. The percentage
of reduction of viable cells was calculated using the following
equation:
2. Experimental
2.1. Materials
Potassium hydroxide, imidazole, sodium p-toluenesulfonate,
1-bromohexadecane, 6-chlorohexanol, 1,4-butanediol, dimethyl
terephthalate, titanium tetrabutoxide, ammonium tetrafluorobo-
rate, ammoniumhexafluorophosphate, potassium perfluorobutane-
sulfonate, potassium trifluoromethanesulfonate and Triclosan
(5-chloro-2-(2,4-dichlorophenoxy)phenol)) (all from Aldrich
Chemicals) were high purity products and were not purified before
use. PBT Valox 195 was a gift of Sabic-IP.
2.2. Instrumental
1H NMR spectra were recorded using a Varian Mercury 400
spectrometer (chemical shifts are downfield from TMS), using
CDCl3 or a CF3COOD/CDCl3 mixture (1/4, v/v) as solvent. The spec-
tra have been recorded just after dissolution in order to avoid the
esterification reaction of end-groups with trifluoroacetic acid.
Gel permeation chromatography (GPC) analysis was performed
using a mixture of chloroform/hexafluoroisopropanol (HFIP) (95/5,
v/v) as eluent (elution rate 0.3 mL minꢀ1) on a Agilent1100 Series
%reduction ¼ ða ꢀ bÞ ꢁ 100=a
where a is the number of viable cells in the control specimen and b
is the number of viable cells in the specimens containing ionic end
groups or triclosan.
apparatus equipped with a Agilent PL Gel 5
l Mini-Mixed-C col-

M. Colonna et al. / Reactive & Functional Polymers 72 (2012) 133–141
135
2.4. Syntheses
and different amounts of 1-hexadecyl-3-(6-hydroxyhexyl)imi-
dazolium salt depending on the ionic concentration to be obtained.
Titanium tetrabutoxide (TBT) (0.106 g, 0.312 mmol, 175 ppm as
titanium with respect to the final polymer weight) was introduced
into the reactor that was closed with a three-neck flat flange lid
equipped with a mechanical stirrer, a torque meter and a heating
band at 90 °C. The system was then connected to a water-cooled
condenser and immersed in a thermostatic salt bath at 215 °C
and the stirrer switched on at 140 rpm. After 2 h, the temperature
was increased to 245 °C, the lid was heated at a temperature of
120 °C and the reactor connected to a liquid nitrogen cooled con-
denser. Dynamic vacuum was then applied to reduce the pressure
down to 0.2 mbar in 60 min. After 75 min the very viscous and
transparent melt was discharged from the reactor.
2.4.1. 1-Hexadecylimidazole
Potassium hydroxide (16.83 g, 0.300 mol) was added to a
dimethyl sulfoxide (DMSO) solution (500 mL) containing imidazole
(13.60 g, 0.200 mol). The mixture was then stirred for 30 min at
70 °C and 1-bromohexadecane (64.12 g, 0.210 mol) was added
dropwise under vigorous stirring. After 6 h, the mixture was cooled
at room temperature and 100 mL of water were added in order to
allow the precipitation of the N-alkylimidazole. The precipitate
was filtered and washed with distilled water (2 L). The washing
procedure was repeated twice.
The final product was dried in an oven under reduced pressure
(yield 95%). 1H NMR (400 MHz, CDCl3, d, ppm from TMS): 0.88 (t,
J = 6.9 Hz, 3H, CH3), 1.20–1.35 (m, 26H, CH2), 1.77 (quintet, 2H,
J = 7.0 Hz, 2H, CH2–C14 chain), 3.92 (t, J = 7.1 Hz, 2H, N–CH2–C15
chain), 6.90 (s, 1H, CH in imidazolium ring), 7.05 (s, 1H, CH in imi-
dazolium ring), 7.46 (s, 1H, N–CH–N in imidazolium ring).
2.4.5. Telechelic PBT ionomers bearing imidazolium end-groups scale-
up polymerization
Micro-pilot plant polymerizations were carried out by using a
two-stage process in a 1.8 L stainless steel batch reactor equipped
with a paddle stirrer (driven at 60 rpm) and a strain-gauge sensor
mounted on the stirrer shaft in order to monitor the viscosity of the
reaction melt (and indirectly the increase of PBT molecular weight)
during the polymerization. Two condensers in series (the first
water-cooled and the second liquid nitrogen-cooled) were con-
nected to the reactor to collect volatile products during the first
and second stages. A typical polymerization procedure is described
below.
2.4.2. 1-Hexadecyl -3-(6-hydroxyhexyl)imidazolium chloride
6-chlorohexanol (16.59 g, 0.121 mol) was added dropwise un-
der vigorous stirring to a solution containing 1-hexadecylimidaz-
ole (32.25 g, 0.100 mol) dissolved in 25 mL of anhydrous toluene.
The solution was stirred for 64 h at reflux temperature. The solvent
was then distilled under reduced pressure. The residue was
washed twice with 500 mL of ethyl acetate and dried under re-
duced pressure (yield 95%). 1H NMR (400 MHz, CDCl3, d, ppm from
TMS): 0.88 (t, J = 6.9 Hz, 3H, CH3), 1.20–1.62 (m, 32H, CH2), 1.72–
2.00 (m, 4H, CH2), 3.58 (t, J = 6.0 Hz, 2H, CH2–OH), 4.32 (dd,
J1 = 7.3 Hz, J2 = 7.5 Hz, 2H, N–CH2–C5 chain), 4.39 (t, J = 7.3 Hz,
2H, N–CH2–C15 chain), 7.40 (s, 1H, CH in imidazolium ring), 7.62
(s, 1H, CH in imidazolium ring), 10.39 (s, 1H, N–CH–N in imidazo-
lium ring).
2.4.5.1. First stage. BD (742.0 g, 8.25 mol), DMT (800.0 g, 4.12 mol)
and 1-hexadecyl-3-(6-hydroxyhexyl) imidazolium tosylate salt
(in different amounts in order to insert ionic groups at a content
0.6, 1 and 2 mol% respect to DMT) were loaded into the reactor
and then heated at atmospheric pressure under stirring to
180 °C. At this temperature, titanium butoxide (1.13 g, 3.31 mmol,
175 ppm as titanium with respect to the final polymer weight) was
introduced into the reactor. The reaction temperature was in-
creased from 180 to 215 °C. Volatile products (methanol and
THF) were distilled off from the reactor, condensed in the water-
cooled condenser and collected in a graduated cylinder. The start
of the first stage was taken when the first drop of liquid was col-
lected in the water-cooled condenser. The temperature was then
kept at 215 °C until 95% of the theoretical amount of methanol
was distilled off. The distilled volume was recorded versus time
as an indicator of the catalytic activity during the first stage and
distillate samples were analyzed by 1H NMR in order to measure
the methanol/THF ratio and thus the rate of THF formation.
2.4.3. 1-Hexadecyl-3-(6-hydroxyhexyl)imidazolium tosylate salt
1-hexadecyl-3-(6-hydroxyhexyl)imidazolium chloride (23.60 g,
0.0550 mol) was dissolved in dichloromethane (DCM) (350 mL)
and added to a solution of sodium p-toluenesulfonate (11.21 g,
0.0578 mol) dissolved in water (190 mL) in a separating funnel.
The content of the funnel was vigorously shaken for 5 min until
no further precipitate was present in the resulting two-phase mix-
ture. This procedure was repeated several times (usually twice) un-
til a silver nitrate test was negative confirming the complete
exchange of the chloride counter-ion. The organic layer was sepa-
rated and the solvent removed under reduced pressure. The yellow
solid was washed twice with ethyl acetate. The product was dried
under vacuum (yield 95%).
1H NMR (400 MHz, CDCl3, d, ppm from TMS): 0.87 (t, J = 6.9 Hz,
3H, CH3), 1.12–1.60 (m, 32H, CH2), 1.79 (m, 2H, CH2), 1.89 (tt,
J1 = 7.1 Hz, J2 = 7.3 Hz, 2H, CH2) 2.33 (s, 3H, CH3 in tosylate ion),
3.57 (t, J = 6.0 Hz, 2H, CH2–OH), 4.18 (dd, J1 = 7.3 Hz, J2 = 7.7 Hz,
2H, N–CH2–C5chain), 4.28 (dd, J1 = 7.1 Hz, J2 = 7.5 Hz, 2H, N–CH2–
C15 chain), 7.16 (d, J = 7.9 Hz, 2H, aromatic CH in tosylate ion),
7.22 (d, J = 1.6 Hz, 1H, CH in imidazolium ring), 7.38 (d, J = 1.6 Hz,
1H, CH in imidazolium ring), 7.77 (d, J = 8.0 Hz, 2H, aromatic CH
in tosylate ion), 9.92 (s, 1H, N–CH–N in imidazolium ring).
The synthesis of the imidazolium salts with other counter-ions
was performed with the same procedure using ammonium tetra-
fluoroborate, ammonium hexafluorophosphate, potassium perfluo-
robutanesulfonate and potassium trifluoromethanesulfonate.
2.4.5.2. Second stage. The internal pressure was slowly reduced,
first from atmospheric pressure down to 10 mbar in 30 min, then
from 10 mbar to 1 mbar in 20 min. At the same time the tempera-
ture of the reaction melt was increased to 240 °C and kept at this
temperature until the end of the polymerization. The start of sec-
ond stage was taken when the minimum pressure was reached.
The second stage was stopped when no further significant increase
in strain gauge signal was detected.
3. Results and discussion
3.1. Monomers synthesis and small scale polymerization
2.4.4. Telechelic PBT ionomers bearing imidazolium end-groups.
Synthesis in glass reactor
A round bottom wide-neck glass reactor (250 mL capacity) was
charged with 1,4-butanediol (BD) (48.88 g, 0.543 mol), dimethyl
terephthalate (DMT) (75.30 g, 0.388 mol) (BD/DMT ratio 1.4/1)
Imidazolium salts need to be modified in order to be inserted at
the end of the polyester chain. The approach we have followed
consists in the derivatization of the imidazolium ring with an alkyl
chain bearing an OH group that can react with the methyl ester
group of DMT and of the growing polymer chain during the poly-

136
M. Colonna et al. / Reactive & Functional Polymers 72 (2012) 133–141
condensation process. Moreover, we have decided to insert a hexa-
decyl alkyl chain on the imidazolium ring in order to impart anti-
microbial properties to the polyester ionomer (Fig. 1).
Imidazolium salts with C4F9SOꢀ and CF3SOꢀ counterions are the
3 3
most stable followed by TsOꢀ. An incomplete exchange of Clꢀ or
Brꢀ ions for more stable counterions is detrimental for the thermal
stability of imidazolium salts and can be revealed by multiple
weight loss steps in TGA curves. For this reason, the exchange
method has been improved with respect to those reported in the
literature [17]. Indeed, an incomplete exchange was observed (by
TGA) using CH3CN as solvents while using a two-phase H2O/CH2Cl2
mixture, the complete exchange was obtained.
The imidazolium salts bearing one long alkyl chain and an OH
group have been prepared from imidazole using a novel synthetic
route (Fig. 2) that consist in the insertion of the first alkyl chain fol-
lowed by the insertion of the hydroxyalkyl chain and then by the
exchange reaction of the chloride ion with the desired counterion.
The synthetic method is versatile and allows the preparation of a
wide range of products with different alkyl chain length and differ-
ent counterions.
The imidazolium salts have been added along with the other
monomers at the beginning of the polymerization of poly(butylene
terephthalate) as reported in the scheme in Fig. 4.
As reported in the literature [17] chloride and bromide salts are
not stable enough to sustain the polymerization and processing
conditions for terephthalate polyesters since they start degrading
below 240 °C. On the other hand, tetrafluoroborate (BFꢀ4 ), hexa-
fluorophosphate (PFꢀ), perfluorobutanesulfonate (C4F9SOꢀ), tri-
The first set of experiments was conducted in small-scale glass
reactors in order to identify the type of counterion having the right
properties required to reach high molecular weight polymers. A
study was performed in order to evaluate the effect of imidazolium
salts on the polymerization rate during the first stage. The reaction
rate was monitored by measuring the amount of methanol distilled
during the first stage. The curves in Fig. 5 show the dramatic effect
of different counterions on catalyst deactivation. In particular
C4F9SOꢀ, PFꢀ and BFꢀ4 completely inhibits the catalyst and only
6
3
fluoromethanesulfonate (CF3SOꢀ3 ) and tosylate (TsOꢀ) salts, that
can be prepared by the counterion exchange procedure described
in step 3 in Fig. 2, are stable at temperatures up to 260 °C, as re-
ported in the TGA curves in Fig. 3.
3
6
low molecular weight oligomers were produced. Tosylate salts
present the optimal combination of properties in terms of high
thermal stability and low deactivation of TBT catalyst. Indeed, with
this counterion it was possible to obtain telechelic imidazolium
polyesters using the normal polycondensation conditions for PBT
(i.e. 1.4 BD/DMT ratio, 175 ppm of TBT as catalyst and 2 h of first
and second stage). Moreover, the amount of THF formed was com-
parable with that recorded in a normal PBT polymerization. The
color of PBT ionomers made using tosylate salts was good since al-
most no discoloration was observed while for the other salts dark
colored materials were obtained.
Fig. 1. Hydroxy-derivatized imidazolium salts with long alkyl chain.
Fig. 2. Synthesis of imidazolium salts bearing hydroxyalkyl groups.

M. Colonna et al. / Reactive & Functional Polymers 72 (2012) 133–141
137
Fig. 3. Thermal stability of 1-hexadecyl-3-(6-hydroxyhexyl)imidazolium salts.
X
CH2 OH
N
6
O
O
HO
CH3 O C
C O CH3
OH
N
CH2 1C5 H3
First stage
215°C 2-4h
Ti(BuO)4 catalyst
Second stage
245°C
dynamic vacuum
O
O C
O
C O
O
CH2
X
N
6N
n
CH3 CH2
15
Fig. 4. Polymerization scheme of PBT imidazolium telechelic ionomers.
Fig. 5. First stage conversion using different counterions and Titanium catalysts.

138
M. Colonna et al. / Reactive & Functional Polymers 72 (2012) 133–141
Table 1
End-groups and molecular weight of ionomers obtaining using 2% of imidazolium salts compared with commercial PBT VALOX 195.
Sample
CH2OH end-groups (%)a
Methyl ester end-groups (%)a
Ionic end-groups (%)a
NMRb Mn
GPCc Mn
GPC PDId
Commercial PBT
Im-TsO
Im-BF4
1.61
0.02
/
0.08
0.03
0.41
6.30
/
26,300
22,100
18,300
4600
24,900
26,000
11,100
2000
2.4
2.8
3.8
2.8
1.91
2.00
1.82
Im-C4F9SO3
1.32
a
b
c
Mol% respect to terephthalate units in PBT.
Molecular weight calculated using end-groups measured by 1H NMR spectroscopy.
Molecular weight calculated using GPC.
d
Polydispersity index measured by GPC.
The results of the molecular characterization of different PBT
sity index below 3 was achieved. This behavior was attributed to
the increased solubility in the reaction mixture of the imidazolium
salt with the long alkyl chain. Moreover, the imidazolium groups
with hexadecyl alkyl chain are also the most interesting in view
of the use of these ionomers for antimicrobial applications [8].
For all the reasons reported above, an imidazolium TsOꢀ salt
bearing a hexadecyl chain and a –(CH2)6OH group has been used
in the scale-up of the experiments in the micro pilot-plant.
telechelic imidazolium ionomers containing 2 mol% of imidazoli-
um groups bearing a hexadecyl alkyl chain and a –(CH2)6OH group
is reported in Table 1.
Using the TsOꢀ imidazolium salt a low level of both methylester
and OH end-groups has been obtained while using the imidazoli-
um BFꢀ4 salt only methylester groups were present in large
amounts. Therefore, in this second case the molecular weight
was limited since methylester groups were not able to react any-
more due to the complete consumption of hydroxyl end-groups.
Moreover, using BF4 salts the Mn calculated by GPC was lower re-
spect to the Mn measured by end-group analysis by NMR since this
second method does not take into account the COOH end-groups
formed by degradation reactions. Using the BF4 salt a longer reac-
tion time was needed in order to obtain a sufficiently high metha-
nol conversion to apply vacuum in the second stage and therefore a
more consistent COOH end-groups formation must be expected.
3.2. Scale-up in micro pilot-plant
The polymerization process using the imidazolium tosylate salt
at 0.6 (Im-TsO-0.6), 1 (Im-TsO-1), and 2 mol% (Im-TsO-2), was then
scaled-up in the 1.8 L micro pilot-plant in order to measure the
THF formation and prepare larger amounts of polymers for further
characterization. The final polymer melt was completely transpar-
ent and clear becoming white after crystallization. No discolor-
ation, presence of solid impurities or side-reactions were observed.
No significant catalyst deactivation was observed following first
stage conversion versus time (Fig. 7) by measuring the amount of
methanol distilled during the first stage in the water-cooled
condenser.
The results of the polymerization are reported in table 2. Ben-
zyltriethylammonium chloride was added to the solvent for inher-
ent viscosity (IV) measurements in order to increase the ionic
strength of the solution and therefore decrease ionic aggregations
between the chain ends [26].
GPC results have to be considered with special care since in the
case of ionomers there is the possibility for ionic aggregation be-
tween the end of chains and for electrostatic interactions with
the column walls. These effects may explain why the molecular
weight values calculated by GPC are higher for the PBT ionomers
with 0.6% of end-groups compared to the normal PBT. This is in
contrast with end-groups analysis that shows comparable amounts
of methyl ester and OH groups. Also COOH end-groups content
should be higher for ionomers due to side-reactions. The higher
amount of side-reactions is confirmed by the analysis of THF
amount formed by side-reactions due to the catalytic effect of imi-
dazolium groups. Therefore, on the basis of end-groups analysis,
the molecular weight should be lower for PBT ionomers due to
the higher content of end-groups (OH, methyl ester, carboxylic
and ionic).
The use of the C4F9SOꢀ salt produces only oligomers with a consis-
3
tent amount of methylester end-groups due to very strong inhibit-
ing effect of the salt on the titanium based catalyst. No vinyl
end-groups were detected by 1H NMR.
The 1H NMR spectra of the imidazolium salt and of the 2%
telechelic ionomer after dissolution in CHCl3/CF3COOH (4/1, v/v)
and precipitation in methanol are reported in Fig. 6.
The presence of the signals of the imidazolium group after the
precipitation in methanol (that is a solvent for the imidazolium
salt) confirms that the ionic groups are covalently bonded to the
polymer backbone. The amount of imidazolium salt was calculated
comparing the signal at d 8.58 ppm (1H of imidazolium salt) with
the signal at d 8.15 ppm (4H of the terephthalate group). OH end-
groups were measured using the peak at d 3.90 ppm (2H) while the
methylester end-groups using the singlet at 4.05 ppm (3H). The 1H
NMR spectrum also shows that no significant side-reactions takes
place during the synthesis, as the peaks in the spectrum are those
expected from the structure of the imidazolium salt added.
A second set of experiments in small-scale glass reactors was
performed in order to define the optimal length of the two alkyl
chains bonded to the imidazolium ring. Using a chain spacer con-
sisting of two methylene units between the OH and the imidazoli-
um ring, only a small amount (below 10%) of imidazolium groups
was bonded to the polymer chain ends (as detected by 1H NMR
after dissolution in CHCl3/CF3COOH (4/1, v/v) and precipitation in
methanol). The low incorporation yield of the imidazolium ionic
groups was attributed to the lower reactivity of the –C2H4OH group
compared to longer alkyl chain spacers. Indeed, using a longer
spacer, with 6 methylene units, an almost complete insertion of
imidazolium groups at the end of the polymer chain was achieved.
Also the length of the non-reactive alkyl chain has an important ef-
fect on the polymerization process. In particular, we have observed
that when imidazolium salts with short alkyl chains were used, the
polydispersity index was high. For example a polydispersity index
of 10 was obtained with an alkyl chain with two carbon atoms. On
the contrary, using longer (hexadecyl) alkyl chains, a polydisper-
IV analysis, on the contrary with respect to GPC measurements,
shows a correlation between ionic content and molecular weight.
Inherent viscosity decreases as expected by increasing the ionic
content, since the imidazolium groups act as end-cappers. Never-
theless, the molecular weight of the ionomers prepared is suffi-
ciently high for several PBT applications.
Thermal properties were investigated by TGA in order to assess
the effect of imidazolium end-groups on the thermal stability of
PBT ionomers. In Table 3 TONSET (the temperature at which the
weight loss in the TGA curve begins), and TD (the temperature at
which the weight loss takes place at the highest rate) are reported.

M. Colonna et al. / Reactive & Functional Polymers 72 (2012) 133–141
139
Fig. 6. 1H NMR of the OH derivatized TsOꢀ imidazolium salt (A) and of the ionomer with 2% TsOꢀ imidazolium after dissolution in CHCl3/CF3COOH (4/1) and precipitation in
methanol (B).
Fig. 7. Conversion during the first stage of PBT synthesis starting from DMT, BD and different amounts of Im-TsO.
From the results obtained, the ionic end-groups have a limited det-
rimental effect on thermal stability. Indeed, a maximum decrease
of 20–24 °C was observed for the ionomer with 2.0 mol% imidazo-
lium tosylate salt. However, the thermal initial degradation tem-
perature of all the ionomers is well above the typical processing
temperature of PBT. The DSC results show that both the melting
temperature and the crystallinity are comparable with those of
standard PBT while the crystallization rate is slightly higher since
in the cooling scan the Tcc is about 4 °C higher, indicating that
the ionic polymers crystallize faster probably due to the lower
Mw or to chemical nucleation effects caused by ionic end-groups
[27].

140
M. Colonna et al. / Reactive & Functional Polymers 72 (2012) 133–141
Table 2
polymerization scale-up results.
Sample
THF in 1st
stage (%)a
Methylester
CH2OH
Ionic
Mn NMRc
Mn GPCd
PDIe GPC
Inherent Viscosity
(dL/g)
end-groups (%)b
end-groups (%)b
end-groups (%)b
PBT control
Im-TsO-0.6
Im-TsO-1
1.80
3.49
6.35
9.57
0.52
0.54
0.31
0.35
1.02
0.98
0.86
0.98
–
28,570
20,750
20,100
13,200
29,800
39,400
28,900
27,800
2.5
2.9
2.8
2.9
0.79
0.77
0.71
0.60
0.60
1.01
2.00
Im-TsO-2
a
b
c
Mol% respect to BD in the feed.
Mol% respect to terephthalate units in PBT.
Molecular weight calculated using end-groups measured by 1H NMR spectroscopy.
Molecular weight calculated using GPC.
d
e
Polydispersity index measured by GPC.
Table 3
Table 4
Thermal properties of the PBT ionomers prepared in the scale-up polymerization.
Percentage of reduction of viable S. aureus and E. coli cells in the treated specimens
compared to the control specimens.
Sample
TD (°C)
TONSET (°C)
Tcc (°C)
D
Hcc
Tm (°C)
DHm
(J/g)
(J/g)
Sample (%)
Reduction of viable cells (%)a
PBT control
Im-TsO-0.6
Im-TsO-1
424
414
420
401
398
388
393
374
176
177
176
180
ꢀ48.0
ꢀ51.6
ꢀ49.7
ꢀ52.1
220
221
221
221
37.9
32.6
39.6
44.0
Staphylococcus aureus
Escherichia coli
Ionic end groups 0.60
Ionic end groups 1.00
Ionic end groups 2.00
Triclosan 0.60
Triclosan 1.00
Triclosan 2.00
89.4 5.7
75.0 6.8
97.5 6.4
83.5 3.6
91.2 3.0
99.4 2.7
26.3 2.9
24.5 3.2
48.5 5.4
42.9 3.8
75.5 5.4
74.6 2.3
Im-TsO-2
TD = temperature of the maximum degradation rate, measured in TGA under N2
flow at 10 °C/min.
TONSET = temperature of the beginning of degradation by TGA weight loss.
Tcc = crystallization temperature measured in DSC during the cooling scan at 20 °C/
min.
Hcc = enthalpy of crystallization.
Tm = melting temperature measured in DSC during the 2nd heating scan at 20 °C/
a
Calculated as follows: % reduction = (a ꢀ b) ꢁ 100/a, where a is the number of
viable cells in the control specimen and b is the number of viable cells in the treated
D
specimens.
min.
D
Hm = enthalpy of fusion.
with PBT at different concentration in a Brabender Plasticorder
mixer obtaining a pale brown material. The results are presented
in Table 4.
The results obtained clearly evidence the high anti-bacterial
effectiveness of the imidazolium telechelic based polymers on
Gram positive bacteria, which is comparable to that of Triclosan
containing specimen. The biological activity of the imidazolium
polymers against E. coli, although lower with respect to Triclosan,
is of great interest considering that, generally, Gram negative
strains are less susceptible to antimicrobial agents, including imi-
dazolium salts [28].
4. Conclusions
We have synthesized for the first time imidazolium telechelic
terephthalate polyesters by adding an imidazolium tosylate salt
bearing a long alkyl chain and a hydroxyl group. The ionic groups
were bonded to PBT chains as end-groups in high yield and they
did not affect properties like color and thermal stability. Using a
tosylate salt no catalyst deactivation has been observed and a nor-
mal polymerization procedure and a standard catalyst loading can
be used. This method can be used for the preparation of imidazo-
lium telechelic ionomers of other polycondensation polymers
(e.g. aliphatic polyesters, polycarbonates and copolymers). The
imidazolium ionomers have proved to be very active against S. aur-
eus even at low concentration (0.6 mol%) while a lower activity has
been observed against E. coli.
Fig. 8. Storage modulus measured by DMTA analysis.
DMTA analysis (Fig. 8) shows that ionomers present a lower
modulus below Tg but a slightly higher modulus above glass tran-
sition temperature. However, a correlation between ionic group
content and thermo-mechanical properties has not been found.
Tg of ionomers measured by DMTA is always comparable with that
of standard PBT.
3.3. Antimicrobial properties
In order to demonstrate the anti-bacterial effectiveness of the
imidazolium telechelic based polymers, specimens containing imi-
dazolium ionic end groups at different concentrations and control
specimens were placed in contact with cells of S. aureus, a Gram
positive bacterium, and E. coli, a Gram negative one. The viability
of the bacteria present on the surface was evaluated and the per-
centage of reduction of viable cells in the treated specimens with
respect to controls was calculated. PBT containing Triclosan was
also tested in order to compare the behavior of telechelic ionomers
with a commercially available AM product. Triclosan was blended
Acknowledgement
This work was financed by SABIC-IP.
References
[1] E. Anderson, T.E. Long, Polymer 51 (2010) 2447–2454.
[2] N. Preethi, H. Shinohara, H. Nishide, React. Funct. Polym. 66 (2006) 851–855.

M. Colonna et al. / Reactive & Functional Polymers 72 (2012) 133–141
141
[3] N. Le Poul, M. Campion, B. Douziech, Y. Rondelez, L. Le Clainche, O. Reinaud, Y.
Le Mest, J. Am. Chem. Soc. 129 (2007) 8801–8810.
[16] C.H. Davis, L.J. Mathias, J.W. Gilman, D.A. Schiraldi, J.R. Shields, P. Trulove, T.E.
Sutto, H.C. Delong, J. Polym. Sci., Part B: Polym. Phys. 40 (2002) 2661–2666.
[17] W.H. Awad, J.W. Gilman, M. Nyden, R.H. Harris, T.E. Sutto, J. Callahan, P.C.
Trulove, H.C. DeLong, D.M. Fox, Thermochim. Acta 409 (2004) 3–11.
[18] A. Eisenberg, M. King, Ion-Containing Polymers, Academic Press, New York,
1977.
[19] W.J. MacKnight, T.R. Earnest, J. Polym. Sci. Macromol. Rev. 16 (1981) 41–122.
[20] J.J. Fitzgerald, R.A. Weiss, Macromol. Chem. Phys. C28 (1988) 99–185.
[21] M.R. Tant, G.L. Wilkes, Macromol. Chem. Phys. C28 (1988) 1–63.
[22] H. Kang, Q. Lin, R.S. Armentrout, T.E. Long, Macromolecules 23 (2002) 8738–
8744.
[4] B. Yu, F. Zhou, H. Hu, C. Wang, W. Liu, Electrochim. Acta 53 (2007) 487–494.
[5] S.-G. Lee, Functionalized imidazolium salts for task-specific ionic liquids and
their applications, Chem. Commun. (2006) 1049–1063.
[6] D. Batra, D.N.T. Hay, M.A. Firestone, Chem. Mater. 19 (2007) 4423–4431.
[7] W. Hilmes, F. Mueller, T. Neil, H. Schramm, (Goldschmidt AG TH) Eur Patent
796557, 1997.
[8] D. Demberelnyamba, K. Ki-Sub, P. Seung-Yeob, L. Huen, K. Chang-Jin, Y. Ick-
Dong, Bioorg. Med. Chem. 12 (2004) 853–857.
[9] S. Borman, Chem. Eng. News 80 (2002) 36–38.
[10] K. Chen, Y. Ku, H. Lin, T. Yan, D. Sheu, T. Chen, J. Appl. Polym. Sci. 100 (2006)
803–809.
[11] S. Konagaya, H. Ohashi, S. Hayakawa, H. Ishihara, T. Endo, Polym. Prepr. 45
(2004) 847–848.
[23] B.J. Chisholm, R.B. Moore, G. Barber, F. Khouri, A. Hempsted, M. Larsen, E.
Olson, J. Kelley, G. Balch, J. Caraher, Macromolecules 35 (2002) 5508–5516.
[24] C. Berti, M. Colonna, E. Binassi, M. Fiorini, S. Karanam, D.J. Brunelle, React.
Funct. Polym. 70 (2010) 366–375.
[12] L. Cen, K.G. Neoh, E.T. Kang, Surface functionalization technique for conferring
antibacterial properties to polymeric and cellulosic surfaces, Langmuir 19
(2003) 10295–10303.
[13] J.C. Tiller, C. Liao, A.M. Klibanov, K. Lewis, Proc. Natl. Acad. Sci. 98 (2001) 5981–
5985.
[14] J. Cohen, T. Abel, M. Filshtinskaya, K. Melkonian, A. Melkonian, D. Burkett, R.
Engel, Abstracts of Papers, 223rd ACS National Meeting, 2002.
[15] G.N. Tew, D. Liu, B. Chen, R.J. Doerksen, J. Kaplan, P.J. Carroll, M.L. Klein, W.F.
DeGrado, Proc. Natl. Acad. Sci. 99 (2002) 5110–5114.
[25] M. Colonna, C. Berti, E. Binassi, M. Fiorini, S. Karanam, D.J. Brunelle, Eur. Polym.
J. 46 (2010) 918–927.
[26] W. Siebourg, R. Lundberg, R. Lenz, K.C. Frisch, Macromolecules 13 (1980)
1013–1016.
[27] R. Legras, C. Bailly, M. Daumerie, J.M. Dekoninck, J.P. Mercier, V. Zichy, E. Nield,
Polymer 25 (1984) 835–844.
[28] L. Carson, P.K.W. Chau, M.J. Earle, M.A. Gilea, B.F. Gilmore, S.P. Gorman, M.T.
McCann, K.R. Seddon, Green Chem. 11 (2009) 492–497.