Formation and characterization of inclusion complexes of alkyne functionalized poly(ε-caprolactone) with β-cyclodextrin. Pseudo-polyrotaxane-based supramolecular organogels

Article abstract of DOI:10.1021/ma102456n

β-Cyclodextrin has been found to form pseudo-polyrotaxanes with propargyl functionalized poly(ε-caprolactone) in N,N-dimethylformamide. The formation of inclusion complexes was proven by ¹H NMR and FT-IR spectroscopy, SEC, dynamic light scatter

Full text of DOI:10.1021/ma102456n

Macromolecules 2011, 44, 375–382 375
DOI: 10.1021/ma102456n
Formation and Characterization of Inclusion Complexes of Alkyne
Functionalized Poly(ε-caprolactone) with β-Cyclodextrin.
Pseudo-Polyrotaxane-Based Supramolecular Organogels.
Olga Jazkewitsch and Helmut Ritter*
Institut of Organic Chemistry and Macromolecular Chemistry II, Heinrich-Heine-University Duesseldorf,
€
Universitatsstrasse 1, 40225 Duesseldorf, Germany
Received October 28, 2010; Revised Manuscript Received November 29, 2010
ABSTRACT: β-Cyclodextrin has been found to form pseudo-polyrotaxanes with propargyl functionalized
poly(ε-caprolactone) in N,N-dimethylformamide. The formation of inclusion complexes was proven by
1H NMR and FT-IR spectroscopy, SEC, dynamic light scattering (DLS), polarized optical microscopy and
wide-angle X-ray diffraction (WAXD). Furthermore, supramolecular organogels based on the pseudo-
polyratoxanes (PPR) were synthesized via 1,3-dipolar cycloaddition of propargyl functionalized poly-
(ε-caprolactone) and mono-(6-azido-6-desoxy)-β-cyclodextrin. The swelling degree and rheological behavior
of the PPR gels were investigated in dependence of the cross-linker content.
Introduction
in the β-CD cavity. In this work we present the formation of
pseudo-polyrotaxanes of β-CD with poly((oxepan-2-one)-co-
Cyclodextrins (CD) are cyclic oligosaccharides and commonly
consisting of 6 (R-CD), 7 (β-CD), or 8 (γ-CD) glucose units
linked by R-1,4 bonds.1 The most important characteristic is their
ability to form selectively inclusion complexes (IC) with other
molecules and polymers.2 Inthe case of polymers the treatment of
cyclodextrin as macrocyclic component onto the backbone or
polymer side chain leads to the formation of so-called pseudo-
polyrotaxane. Since 1990 Harada et al. reported that R-CD forms
an IC with poly(ethylene glycol) in aqueous solution,3 a great
number of polymeric cyclodextrin complexes with different types
of CDs were prepared and characterized.4-9 Remarkable in these
studies was the fact that the selectivity in complex formation of
polymeric compounds with CDs is higher than for low molecular
weight molecules. Harada and Kamachi found, for example, that
β- and γ-CD form IC with poly(propylene glycol) in contrast to
R-CD that does not form IC with PPGs of any molecular weight.10
These results indicate that besides the main driving forces of the
complex formation such as hydrophobic and van der Waals
interactions as well as hydrogen bonding,11 the sizes of the cyclo-
dextrin cavities and the cross-sectional areas of the polymers are
very important for the IC formation.11 In different studies the
formation of pseudo-polyrotaxane (PPR) structures between cyclo-
dextrins and many biodegradable polyesters has been investi-
gated, such as poly(ethylene adipate),12 poly(lactide),13,14 and
bacterial poly(3-hydroxybutyrate).15 The preparation and char-
acterization of inclusion complexes from CDs with poly-
(ε-caprolactone) (PEC) were also reported. The first report on
complex formation of poly(ε-caprolactone) and CD by Harada
et al. was investigating R-cyclodextrin.16 In this study, they demon-
strated a complex formation of R-CD with PEC not only in aqueous
solutions but also in N,N-dimethylformamide (DMF). In a later
study, the complex formation with γ- and β-CD was found. β-CD
((3/7-prop-2-ynyl)oxepan-2-one)) that was investigated by differ-
ential scanning calorimetry, 1H NMR and FT-IR spectroscopy,
SEC, DLS, WAXD, and polarized optical microscopy. Further-
more, organogels based on these pseudo-polyrotaxanes were
synthesized. Their swelling degree and rheological properties
were examined.
Experimental Section
Materials. β-Cyclodextrin was obtained from Wacker-Chemie
GmbH (Burghausen, Germany) and used after drying overnight
in a vacuum oil pump over P4O10. ε-Caprolactone (ε-CL) was
purchased from Acros, dried over calcium hydride, distilled under
reduced pressure and stored over molecular sieves (0.4 nm) under an
argon atmosphere. Cyclohexanone was purchased from Aldrich,
dried over magnesium sulfate and distilled before use. Sodium
ascorbate (AppliChem) and copper(II) sulfate (Carl Roth GmbH)
were used as received. Commercially available reagents and solvents
were used without further purification. Propargyl bromide (80 wt %
solution in toluene) and lithium N,N-diisopropylamide solution
(2.0 M in THF/heptanes/ethylbenzene) were purchased from Acros
Organics and from Sigma-Aldrich, respectively. m-Chloroperben-
zoic acid (70-75%) was purchased from Sigma-Aldrich and used as
received.
1
Measurements. H NMR and 13C NMR spectroscopy was
performed using a Bruker Advance DRX 500 spectrometer at
500.13 MHz and at 125.77 MHz in DMSO-d6 and CDCl3 as
solvent, respectively. Chemical shifts were referenced to the
solvent value δ = 2.5 ppm for DMSO-d6 and δ = 7.26 ppm
for CDCl3. IR measurements were performed using a FT-IR
spectrometer Nicolet 6700 FT-IR equipped with an ATR unit.
Molecular weights and molecular weight distributions were
measured by size exclusion chromatography (SEC) using a
Viskotek GPCmax VE2001 system that contained a column
set with one Viskotek TSK guard column HHR-H 6.0 mm (ID) ꢀ 4
cm(L) andtwo Viskotek TSK GMHHR-M 7.8 mm (ID) x 30 cm
(L) columns at 60 °C. N,N-Dimethylformamide (DMF, 0.1 M
formed complexes with PECs (Mn = 2000-3000 g mol-1) in
3
only moderate yields from aqueous solution.17 Harada et al.
suggested that the polymer chain of PEC is too slim to fit snugly
LiCl) was used as eluent at a flow rate of 1 mL min-1
A Viskotek VE 3500 RI detector and a Viskotek Viscometer model
.
3
*Corresponding author. E-mail: h.ritter@uni-duesseldorf.de.
r 2010 American Chemical Society
Published on Web 12/23/2010
pubs.acs.org/Macromolecules

376 Macromolecules, Vol. 44, No. 2, 2011
Jazkewitsch and Ritter
250 were used for detection. The system was calibrated with
polystyrene standards with a molecular range from 580 D to
1186 kDa. Gas chromatography/mass spectrometry (GC/MS)
measurement was accomplished on a Thermo Finnigan Trace
DSQ system. The ionization occurred by means of electron
impact (EI). Differential scanning calorimetry (DSC) measure-
ments were performed using a Mettler Toledo DSC 822 con-
troler apparatus in a temperature range between -50 and 350 °C
2930 (m, CH), 2859 (m, C-H), 1703 (s, CdO), 1450, 1424,
1129 cm-1
.
Synthesis of 3-/7-(Prop-2-ynyl)oxepan-2-one (2a/b). 2-Prop-2-
ynyl-cyclohexanone (60 mmol) was added to a solution of
m-chloroperbenzoic acid (90 mmol, 20.18 g) in 160 mL methy-
lene chloride. The reaction mixture was refluxed for 48 h. After
cooling to room temperature and filtration, the solution was
washed twice with aqueous sodium sulfite and aqueous sodium
hydrogen solutions. Subsequent removal of the solvent under
reduced pressure and distillation under oil pump vacuum
yielded 80% of the product as an isomeric mixture (3- (70%)
and 7-(prop-2-ynyl)oxepan-2-one (30%)). 1H NMR (500 MHz,
CDCl3, ppm): δ 4.35-4.16 (m, 3H), 2.77-2.72 (m, 1H),
2.66-2.52 (m, 5H), 2.43 (ddd, J = 16.7 Hz, 8.1 Hz, 2.7 Hz,
1H), 2.31 (ddd, J = 17.1 Hz, 9.2 Hz, 2.6 Hz, 1H), 2.18-2.06
(m,2H),2.00-1.88 (m, 5H), 1.72-1.37(m,6H).13CNMR(125Hz,
CDCl3, ppm): δ 176.0, 174.6, 82.4, 80.02, 77.6, 71.3, 70.2, 68.5,
42.0, 34.7, 33.6, 28.9, 28.8, 28.0, 27.8, 26.1, 22.9, 21.9. FT-IR
(diamond): ν = 3277 (w, -CtCH, C-H), 2933, 2859 (m, C-H),
1723 (s, CdO), 1443, 1289, 1174, 1051 cm-1. GC/MS: m/z = 153
[M þ H]þ, 152 [M]þ, 135, 97, 79, 77, 65, 39. Anal. Calcd (C9H12O2):
C, 71.0; O, 21.0; H, 7.9. Found: C, 69.7; O, 22.1; H, 8.2.
with a heating rate of 10 °C min-1. The reported melting point
3
(Tm) values are taken from the third heating cycle. Thermo-
gravimetric analysis (TGA) was performed using a Perkin-
Elmer STA 600 thermal analysis apparatus. The samples were
heated from 30 to 800 °C under argon atmosphere with a heating
rate of 10 °C min-1. The measurements were baseline corrected
3
and analyzed by Pyris software. Wide-angle X-ray diffraction
(WAXD) measurements were performed with a Huber Guinier
(System 600) X-ray diffractometer with a Cu KR radiation
˚
source (λ = 1.54 A). The diffraction intensities were measured
from 2Θ = 3° to 60° at a rate of 2Θ = 3°/min. Dynamic light
scattering measurements were carried out at 25 °C using a Malvern
Zetasizer Nano ZS ZEN3600 instrumentation with a laser wave-
length of 633 nm and a detection angle of 173°. The polymer
concentration was 0.2 mg ml-1. The solutions were filtered
Copolymerization of 3-/7-(Prop-2-ynyl)oxepan-2-one (2a/b)
and ε-CL. To the mixture of 3-/7-(prop-2-ynyl)oxepan-2-one and
ε-CL (ratio 1:9, 1:7, 1:5) in a round-bottom flask purged with argon,
0.5 mol % of Sn(Oct)2 was added as a catalyst. The flask was
immersed in an oil bath at 100 °C for 24 h. After cooling to room
temperature the product was dissolved in CH2Cl2, precipitated twice
in cold methanol and dried in vacuum. The yield was estimated
3
through 0.45 μm Chromafil Xtra syringe filters prior to mea-
surements. The particle size distribution was derived from a
deconvolution of the measured intensity autocorrelation func-
tion of the sample by the general purpose mode algorithm included
in the DTS software. Elemental analysis was performed with a
Perkin-Elmer 2400 CHN analyzer. Polarized optical micro-
scopic (POM) observation was performed on an Olympus BH-2
polarizing microscope equipped with a digital camera. The dried
gels were swollen in an excess of DMF for 48 h, respectively. The
swelling degree was determined gravimetric and calculated
according to the equation:
1
gravimetrically (98-99%). H NMR (500 MHz, CDCl3, ppm):
δ 4.9 (m, 1H), 4.03 (t, J = 6.6 Hz, 2H), 2.28 (t, J = 7.4, 2H), 1.97
(m, 2H), 1.62 (m, 4H), 1.35 (m, 2H). 13C NMR (125 Hz, CDCl3,
ppm): δ 173.6, 173.5, 173.0, 79.6, 71.3, 70.6, 70.1, 64.2, 28.4, 25.6,
24.8, 24.6, 23.9. FT-IR (diamond): ν = 3277 (w, -CtCH, C-H),
2943 and 2863 (m), 1723 (s, CdO), 1241, 1161 (s, C-O), 962 cm-1
.
Q ¼ ðmS - mDÞ=mD
Preparation of β-Cyclodextrin Inclusion Complexes (3a-c-β-CD)
with Copolymers 3a-c. A solution of 0.3 g polymer and
β-cyclodextrine (equivalent amount relating to the alkyne
group of the copolyester) dissolved in 5 mL of DMF was
placed in an oil bath at 70 °C for 12 h and then stirred at 21 °C
for 36 h. The reaction product was precipitated in diethyl ether and
dried in vacuum. The yield was estimated gravimetrically (99%).
1H NMR (500 MHz, DMSO-d6, ppm): δ 4.9 (m, 1H), 4.03 (t, J =
6.6 Hz, 2H), 2.28 (t, J = 7.4 Hz, 2H), 1.97 (m, 2H), 1.62 (m, 4H),
1.35 (m, 2H). FT-IR (diamond): ν = 3328 (m, OH), 2937 and 2859
mS and mD are the weights of the swollen and dried gels,
respectively. The rheological characterization of the DMF
swollen pseudo-polyrotaxane-based gels was performed using a
Thermo Scientific HAAKE Mars viscosimeter in a parallel plate
configuration using a MP35/S plate and a PP35/S with a diameter of
35 mm and a serrated surface. Rheological properties were studied
in oscillatory experiments; mechanical spectra were recorded in
the frequency range of 0.01-10 Hz. The linear viscoelastic
region was assessed by amplitude sweep with a shear stress at
0.001-1 Pa.
(m), 1723 (s, CdO), 1241, 1154 (s, C-O), 1026 cm-1
.
Preparation and Properties of Pseudo-Polyrotaxane-Based
Gels (PPRG). Mono-(6-azido-6-desoxy)-β-cyclodextrin (an equiva-
lent compared to the alkyne group of the copolyester) was added to a
solution of 400 mg polyester 3a-c in 2 mL of DMF. The solution of
10 mol % sodium ascobate and 5 mol % copper(II) sulfate penta-
hydrate in 0.3 mL of DMF was filtered through 0.45 μm Gelman
Acrodisk syringe filters and added to the solution of the polyester
and β-CD-N3. The flask was immersed in an oil bath at 70 °C for
1 h. To examine the swelling behavior of the gels and their rheological
properties, thin cylindrical shaped gels were prepared in two Teflon
round molds with an internal diameter of 3 cm. For this purpose
1 mL of reaction mixture was poured into the mold and dried in a
drying oven at 90 °C for 24 h. FT-IR (diamond): ν = 3356 (m, OH),
2940 and 2863 (s, CH2,CH3, C-H), 1726 (s, CdO), 1655 (w), 1154
Synthesis. Synthesis of 2-Prop-2-ynyl-cyclohexanone (1).
A 250 mL round-bottom flask was purged with argon and cooled
in a dry ice/acetone bath. A solution of lithium diisopropyla-
mide (120 mmol) was added to the round-bottom flask and
stirred for 30 min. An argon-purged solution of cyclohexanone
(120 mmol) in 3 mL of THF was added dropwise to the LDA
solution keeping the solution at -70 °C. Propargyl bromide (120
mmol) in 10 mL of THF was also added dropwise by a syringe
and the solution was stirred for additional 60 min. The reaction
mixture was then warmed up to room temperature and stirred
overnight. The reaction was quenched with an excess of aqueous
ammonium chloride, washed twice with diethyl ether, dried over
MgSO4 and the solvent was evaporated. The following distilla-
tion under reduced pressure (T = 45 °C, p = 0.34 mbar) afforded 1
(w), 1026 cm-1
.
1
as a colorless liquid (56% yield). H NMR (500 MHz, CDCl3,
ppm): δ 2.56 (ddd, J = 17.1 Hz, 4.6 Hz, 2.7 Hz, 1H), 2.48-2.42
(m, 1H), 2.39-2.34 (m, 2H), 2.30-2.23 (m, 1H), 2.13 (ddd, J =
17.0 Hz, 8.4 Hz, 2.6 Hz, 1H), 2.07-2.03 (m, 1H), 1.92 (t, J =
2.6 Hz, 1H), 1.89-1.86 (m, 1H), 1.70-1.55 (m, 2H), 1.37 (ddd,
J = 25.4 Hz, 12.7 Hz, 3.6 Hz, 1H). 13C NMR (125 Hz, CDCl3,
ppm): δ 210.9, 82.7, 69.5, 49.6, 42.05, 33.3, 27.9, 25.2, 18.9. GC/
MS (EI): m/z = 137 [M þ H]þ, 136 [M]þ, 135, 108, 107, 93, 79,
77, 65, 55, 39. FT-IR (diamond): ν = 3290 (w, C-H, -CtCH),
Results and Discussion
Synthesis of Alkyne-Functionalized Polyester. The strategy
for the synthesis of functionalized aliphatic polyester bearing
propargyl group relies on the copolymerization of ε-capro-
lactone and the propargyl functionalized lactone 3-/7-(prop-
2-ynyl)oxepan-2-one (2a/2b) via Sn(Oct)2-mediated ring-
opening polymerization (ROP). The functionalized lactone

Article
Scheme 1. Synthesis of Alkyne-Functionalized Lactones 2a and 2b
Macromolecules, Vol. 44, No. 2, 2011 377
Table 1. Results of the Copolymerization of 2a/2b and ε-CL
feed
ratio
(2a/b: ε-CL)
incorporation
ratiob (2a/b:
ε-CL) (mol %)
a
c
Mn
(g mol-1
Tm
(°C)
entry
)
PDa
3
3a
3b
3c
32 700
36 700
28 640
2.6
2.5
3.5
1:9
1:7
1:5
8:92
10:90
13:87
47.5
41.4
36.5
a Determined by SEC in DMF relative to polystyrene standards.
b Determined from 1H NMR spectra. c DSC, determined from third
heating cycle.
Table 2. Measurement Results of the Copolyesters 3a-c and Their
β-CD Inclusion Complexes 3a-c-β-CD
Scheme 2. Synthesis of Functionalized Precursor Polyester 3a-c by
ROP of Lactones 2a and 2b and ε-CL
a
c
c
Mn
(g mol-1
d
Tm
ΔHm
(J/g)
content
of CD (mol %)b
entry
3a
3a-β-
CD
3b
3b-β-
CD
3c
3c-β-
CD
)
PDa (nm) (°C)
3
32 700
62 930
2.6
1.6
12.2 47.5
17.3 45.1
52.2
18.8
8.3
10.5
15.7
36 700
48 200
2.5
2.2
9.2 41.4
12.3 38.7
36.2
14.6
28 640
35 600
3.5
3.1
11.7 36.5
14.1 35.9
32.8
14.3
a Determined by SEC in DMF relative to polystyrene standards.
b Determined by 1H NMR spectra from signals at 3.098 ppm (O-
CH2(CH2)3 from copolymer) and 3.63-3.54 ppm (H3,5,6,6 from β-CD).
c DSC, taken from the third heating cycle.
nearly complete consumption of lactone 2a/b during the
polymerization.
2a/2b was prepared in two steps. At first, 2-prop-2-ynyl-
cyclohexanone (1) was obtained according to Scheme 1 from
cyclohexanone by reaction with lithium N,N-diisopropyla-
mide (LDA) and a toluene solution of propargyl bromide
at -78 °C. The distilled product was further reacted with an
excess of m-chloroperbenzoic acid in methylene chloride as
solvent (Baeyer-Villiger oxidation). Subsequent distillation
under oil pump vacuum afforded an isomeric mixture 2a/2b in
Furthermore, the thermal behavior of resulting copolymers
3a-c was investigated by DSC measurements. As expected,
the melting point of the copolymers decrease with increasing
incorporation of acetylene functionalized lactones 2a/b, because
these disrupt the formation of crystalline domains, which are
characteristic for poly(ε-caprolactone) and other aliphatic
polyesters.18-20 The nearly complete incorporation of ε-CL
and lactones 2a/b and the thermal properties of 3a-c indicate
that the obtained copolyesters are random copolymers.
Complex Formation of Copolyesters 3a-c with Unmodified
β-CD. As mentioned above, cyclodextrins are able to include
polymers as guests within their hydrophobic cavity. A large
number of studies on complexes of R-, β-, γ-CDs with various
polymers have been described in the literature. With this
intention the copolyester 3a-c was treated with β-CD in
DMF at 80 °C, precipitated (entry 3a-c-β-CD) and investi-
gated by SEC, FT-IR, DLS, DSC and NMR. Table 2 lists the
results of the studies.
The SEC measurements of the precursor copolymers 3a-c
and of the corresponding pseudo-polyrotaxanes 3a-c-β-CD
in DMF revealed that no free β-CD is present and that Mn of
pseudo-polyrotaxanes is higher than Mn of the copolymers
before the treatment with β-CD. Furthermore, the polydis-
persity indexes of inclusion complexes (IC) are lower than
the PD of copolyesters 3a-c. It was found that the curves
differ from each other particularly in the range of low molar
masses. Possible explanation for these differences is a better
threading of the low molecular polymer chains into the β-CD
cavity than that of the high molecular polymer chains. This
process effects the narrower molecular mass distribution of
the complexes 3a-c-β-CD. The size of copolyesters 3a-c and
their complexes was also investigated in DMF solution by
DLS measurements (Table 2). The hydrodynamic diameter
of copolyesters increased after the complexation with β-CD.
Obviously the treatment of copolyester 3a-c with CD leads
to the slight extension of the polymer chain, as would happened
in the case of complex formation.
1
80% yield. The lactone mixture was characterized by H,
13C NMR and FT-IR spectroscopy.
The FT-IR spectrum reveals an acetylene C-H stretching
at 3277 cm-1 and a signal at 1723 cm-1, corresponding to the
carbonyl band of the ester group. The H NMR-spectro-
1
scopic investigation of isomeric mixture show several over-
lapping signals in the region at 4.35-4.16 ppm (correspond-
ing to CH2OC=O and CHOC=O) as well as in the range of
2.75 to 1.37 ppm (corresponding to the protons of the lactone
ring). From the 13C NMR the ratio between 2a and 2b is
accessible by integration of the carbonyl carbon signals at
176.03 and 174.62 ppm. It was found that the lactones mixture
consists of 70% lactone 2b and 30% lactone 2a. For the
following experiments, the isomeric mixture was used with-
out further separation.
The copolymerization of lactones 2a/b and ε-CL feeding
different ratios of monomers was carried out using 0.5 mol %
Sn(Oct)2 as catalyst (Scheme 2). The polymerization was per-
formed at 100 °C, yielding copolymers of type 3. Table 1
summarizes some characteristic data of the obtained poly-
mers 3a-c.
The molar content of 2a/b incorporated into the copoly-
mers 3 was calculated by integration of the 1H NMR spectral
signals (Figure 1) at δ = 1.97 ppm (CtCH from monomers
2a/b) and at δ=4.9 ppm (CH2O of the polymer backbone
from 2b) compared to the signal at δ=4.03 ppm (CH2O of
the polymer backbone from 2a and ε-CL). The data show
that the polymerizability of ε-CL is higher compared to the
substituted lactones 2a and 2b. Anyway, the incorporation
ratio differs just a little from the feed ratio, indicating a

378 Macromolecules, Vol. 44, No. 2, 2011
Jazkewitsch and Ritter
Figure 1. 1H NMR (500 MHz, in CDCl3) spectrum of the alkyne functionalized copolyester 3b.
Table 3. Complexation Shifts Δδa of the Protons of β-CD and Copolyester Induced by the Inclusion of Copolyester in the CD Cavity
β-CD
copolyester 3
0
protons
Δδa [ppm]
H3
-0.02
H5
-0.03
H6,6
0
H1
0
OH6
þ0.02
OH2,3
þ0.03, þ0.01
H2,H4
þ0.02
A1-2
-0.01
B1-3, D1-3
-0.01
C1-3
-0.01
a Determined by 1H NMR spectra (in DMSO-d6) of the free compounds (f) and the inclusion complex 3a-c-β-CD (ic). The complexation induced
shift is defined as: Δδ = δf - δic
.
1H NMR spectroscopy was used to investigate the host-
guest compounds 3a-c-β-CD (see Figure 1 for the spectrum
of 3b). The analysis of chemical shift variations of protons
provides some evidence which of them are involved in the
interaction. In this connection, numerous studies indicate
that the signals of the cavity protons of β-CD show a high-
field shift upon complexation with a suitable guest.21 By
comparison, the protons of the guests can show as well the
downfield as highfield shift.22,23
Hence, the formation of inclusion complexes with unmodi-
fied β-CD was studied by comparing of the 1H NMR spectra
of β-CD, pure copolyester 3a-c and the corresponding
inclusion complexes 3a-c-β-CD (Table 3). The comparison
revealed that the β-CD protons of IC located outside the
cavity show downfield shifts, whereas the peaks of H3 and H5
protons which are located inside the cavity move to higher
fields. Furthermore, the protons of copolyester backbone also
undergo highfiled shifts, indicating the interaction between the
cavity of β-CD and copolyester chain in the inclusion com-
plexes 3a-c-β-CD.
The DSC analysis was performed to study the influence of
β-CD in the ICs on the crystallinity of the copolyester chains.
The thermal properties of the pure copolyesters 3a-c and
their β-CD inclusion complexes were investigated in the tem-
perature range from -30 to 350 °C. The complexes 3a-c-β-CD
show an endothermic peak between 30 to 50 °C (Figure 2). The
transition temperatures are slightly lower than the melting points
of the pure precursor polymers 3a-c. Generally, the complete
CD-polymer ICs with channel structure24 have no melting
point, but they decompose above 310 °C.25,26 Hence, these
peaks can be attributed to the melting process of the crystal-
line domains of the uncovered polyester chains of the partial
Figure 2. DSC thermogram of copolymers 3a-c and of the corre-
sponding pseudo-polyrotaxanes 3a-c-β-CD obtained from the third
heating cycle.
inclusion complexes (Figure 3). The obtained enthalpies of
fusion ΔHm for the pseudo-polyrotaxanes 3a-c-β-CD deviate
significant from the enthalpies of fusion for the untreated
copolymers 3a-c (Table 2). The ΔHm values of pure poly-
esters are approximately twice as high as the ΔHm values of
the corresponding β-CD complexes. This suggests that the
building of inclusion complex decreases the degree of crystal-
linity of the polyesters.
It may be supposed that the crystallization is restricted,
becausetheregularchaintochaininteractionofthepolyesters is

Article
Macromolecules, Vol. 44, No. 2, 2011 379
Figure 5. Thermogravimetric analysis of β-CD, copolyester 3a-c
and the corresponding inclusion complexes. The heating rate was
10 °C min-1, and the measurements were performed under argon
Figure 3. Schematic representation of the proposed reorganization of
polymer through formation of inclusion complex (a and b). Compar-
ison between photographs of a spherulite of 3b and optic appearance of
3
atmosphere.
3b-β-CD obtained by polarized light microscopy (POM) (5 mg ml-1 in
3
DMF).
Figure 6. FT-IR spectra of copolyesters 3a-c and the corresponding
β-CD inclusion complexes.
Figure 4. X-ray diffraction patterns of β-CD and partial IC 3c-β-CD
with channel structure.
disturbed by the inclusion also the mobility of the polymer
segments is reduced in the pseudo rotaxane areas (Figure 3a,b).
The POM photographs (Figure 3) of the copolymer 3b and
the corresponding pseudo-polyrotaxane 3b-β-CD indicate
that the formation of the relative large spherulites such as in
copolyester 3b was inhibit due to pseudo-polyrotaxane units.
The formation of partial copolyester IC with channel
structure was supported by WAXD measurements. Figure 4
Figure 7. FT-IR spectra of the copolyesters 3a-c and the correspond-
ing β-CD inclusion complexes in the region from 3000 to 3700 cm-1
.
shows the X-ray powder patterns of the IC 3c-β-CD in
comparison with pure β-CD.

380 Macromolecules, Vol. 44, No. 2, 2011
Jazkewitsch and Ritter
Scheme 3. Product of Huisgen-type 1,3-Dipolar Cycloaddition of Copolyester 3a-c and β-CD-N3
Actually, the IC of CDs can be roughly classified as either
“cage-type” or “channel-type”.27 The pattern of the inclu-
sion complex sample (Figure 4) is different from the pattern
of the pure β-CD, where CD molecules are arranged in a
“cage-type” packing. The partial IC 3c-β-CD sample shows
prominent peaks at 21.6° and 23.9°, which were consistent
with that of linear unmodified poly(ε-caprolactone).28,29
Furthermore, the diffractogram of IC reveals the character-
istic peaks at about 12.6° (0.7 nm) and 19.6°(0.45 nm). A similar
values were observed by Li et al. in the case of polyolefin β-CD
channel complexes.30 The reflection peak at 2θ = 6.3° (1.4 nm)
can be attributed to the dimension of two β-CDs. This shows
that, copolyesters 3a-c formed with β-CD a partially com-
plexes with channel type structure (Figure 3b).
The thermal stability of partial β-CD-copolyester ICs,
pure copolyester and β-CD was investigated by thermo-
gravimetric analysis (Figure 5).
The thermogravimetric curves of the pure copolyesters
3a-c and β-CD follow a one-stage decomposition process,
whereas the profiles of β-CD-copolyester ICs show a two-
step thermal decomposition. The first step is attributed to
decomposition of β-CD at about 255 °C and shows some
lower decomposition temperature (at 278 °C) than the pure
β-CD. The second degradation step is attributed to the free
copolyester component. The similar behavior was observed
by Bullions et al. for the ICs formed between γ-CD and
poly(ethylene terephthalate).31
Figure 8. FT-IR spectra of the copolyesters 3b and the pseudo-poly-
rotaxane-based gel 5b.
Obviously, the shift of the carbonyl band of the copoly-
esters is due to the formation of hydrogen bonds with the
hydroxyl groups of β-CD. According to this fact, a spectro-
scopic difference should be found in the region from 3100 to
3400 cm-1 of symmetric and asymmetric vibrations of the
OH groups.35
As shown in Figure 7, the peak of the OH-stretching band
of β-CD at 3313 cm-1 shifts to 3353 cm-1 in the case of the
inclusion complex with the polyesters 3a-c. This is shown by
a dashed line in the Figure 7. It can be thus assumed that the
shift mainly is due to the formation of hydrogen bonds
between the carbonyl groups of polyesters and the hydroxyl
groups of CDs. These studies provide evidence for the
hypothesis that β-CD-N3 should also be able to include
polyester under the same conditions.
Finally, FT-IR measurements of the polymers and IC in
the region from 750 to 4000 cm-1 were performed to receive
more information concerning the formation and phase structure
of the samples. The carbonyl absorption bands are shown in
Figure 6. The IR spectra of pure semicrystalline polymers
3a-c exhibit a carbonyl stretching band (s, ν CdO) at ∼1722
cm-1 and a shoulder at ∼1736 cm-1, corresponding to the
carbonyl absorption of the crystalline phase and of the
amorphous region of the copolyester, respectively.32-34 The
FT-IR spectra of the pseudo-polyrotaxanes exhibit the peak
of the amorphous band with a slightly increase of intensity
according to the results of DSC measurements. Furthermore, a
Synthesis of the Pseudo-Polyrotaxane-Based Organogels
via Click Reaction. In addition, pseudo-polyrotaxane-based
gels were formed in DMF solution reacting copolyester 3a-c
new peak appears at ∼1724 cm-1
.

Article
Macromolecules, Vol. 44, No. 2, 2011 381
Figure 9. Photographs of a form stable pseudo rotaxane-based gels swollen for 48 h with DMSO (left), swollen for 48 h with DMF (right) and the
original size after synthesis (middle).
Figure 11. Frequency dependency of storage modulus G0 (closed
symbols) and loss modulus G00 (open symbols) for PPR-based gels
Figure 10. Swelling ratio Q of PPR-based gels 5a (square), 5b (circle)
and 5c (triangle) in DMF versus the swelling time at 23 °C.
containing 8.3% (square), 10.5% (circle) and 15.7% (triangle) of
β-CD-N3 swollen with DMF.
with pendant alkyne groups with mono-(6-azido-6-desoxy)-
β-cyclodextrin (Scheme 3). Mono-(6-azido-6-desoxy)-β-
comprising 8.3 mol % of β-CD-N3 reached 10, whereas 5c
cyclodextrin (β-CD-N3) was synthesized according to a
(15.7 mol % of β-CD-N3) possessed the swelling ratio of
only 8.
method described in the literature.36 The polymer network
5a-c is a result of the formation of pseudo-polyrotaxane
(PPR) by incorporation of polyester chain into the cavity of
β-CD-N3 and at the same time occurring click reaction.
The FT-IR spectra of the reaction product (Figure 8)
exhibit a carbonyl stretching band of polyester at 1726 cm-1
Figure 11 shows the frequency dependence of the storage
modulus G0 and loss modulus G00 of pseudo-polyrotaxane-
based gels 5a-c swollen in DMF. For all PPR gels swollen in
DMF the values of the storage moduli were almost constant
and were sufficiently higher than the corresponding values of
the loss moduli in the whole frequency range, indicating that
these gels behave as a viscoelastic solid. The storage modulus
increased with the increase of cross-linker content.
and the peak of the OH stretching band of β-CD at 3353 cm-1
.
A new peak at 1655 cm-1, specific for carbon-carbon
double bond which, associated with the vibration of carbon-
nitrogen bond at 1026 cm-1, prove the formation of triazole
ring by the “click” reaction. The barely visible peak at
2105 cm-1, corresponding to the specific vibration of the
azide group suggests that almost all of β-CD-N3 molecules
threaded onto the polyester chains were reacted during this
procedure.
Conclusion
A propargyl-functionalized ε-caprolactone was successful
ring-opened copolymerized with ε-caprolactone yielding an ali-
phatic copolyester with a pendent propargyl group. It was found
that the synthesized copolyesters form inclusion complexes with
unmodified β-CD in DMF. These obtained pseudo-polyrotax-
It was found that the obtained gels 5a-c swell in DMF or
in DMSO (Figure 9). To examine the swelling behaviors of
the gels and their rheological properties, thin cylindrical-shaped
gels were immersed in DMF.
The swelling measurements of PR-based gels 5a-c were
carried out by monitoring the weight change over the swell-
ing time. Highly cross-linked gels have a tighter network
structure and swell less than those with a lower cross-linking
density. The equilibrium swelling state was reached after
80 min. As shown in Figure 10, the swelling ratios of the PR
gels in DMF decreased with the increase in amount of “cross-
linker” β-CD-N3. Accordingly, the swelling ratio of gel 5a
1
anes were investigated by H NMR and FT-IR spectroscopy,
DLS, SEC, and WAXD. The thermal behavior was determined
by DSC and TGA. All the studies supported the formation of
proposed pseudo-polyrotaxane. The alkyne group consisting
copolyesters 3a-c were further reacted with β-CD-N3. The
1,3-dipolar cycloaddition led to formation of organogels, which
are swellable in DMF and DMSO. In addition, the swelling
degrees of the supramolecular gels depend on the degree of the
supramolecular cross-linking. The rheological investigation
showed a viscoelastic behavior of the synthesized organogels

382 Macromolecules, Vol. 44, No. 2, 2011
Jazkewitsch and Ritter
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