Synthesis and characterization of poly(ε-caprolactone-co-δ- valerolactone) with pendant carboxylic functional groups

Article abstract of DOI:10.1002/cjoc.201190088

In this paper, aliphatic polyesters functionalized with pendant carboxylic groups were synthesized via several steps. Firstly, substituted cyclic ketone, 2-(benzyloxycarbonyl methyl)cyclopentanone (BCP) was prepared through the reaction of enamine with benzyl-2-bromoacetate, and subsequently converted into the relevant functionalized δ-valerolactone derivative, 5-(benzyloxy carbonylmethyl)-δ-valerolactone (BVL) by the Baeyer-Villiger oxidation. Secondly, the ring-opening polymerization of BVL with ε-caprolactone was carried out in bulk using stannous octoate as the catalyst to produce poly(ε-caprolactone-co-δ-valerolactone) bearing the benzyl-protected carboxyl functional groups [P(CL-co-BVL)]. Finally, the benzyl-protecting groups of P(CL-co-BVL) were effectively removed by H₂ using Pd/C as the catalyst to obtain poly(ε-caprolactone-co-δ-valerolactone) bearing pendant carboxylic acids [P(CL-co-CVL)]. The structure and the properties of the polymer have been studied by Nuclear Magnetic Resonance (NMR), Fourier Infrared Spectroscopy (FT-IR) and Differential Scan Calorimetry (DSC) etc. The NMR and FT-IR results confirmed the polymer structure, and the ¹³C NMR spectra have clearly interpreted the sequence of ε-caprolactone and 5-(benzyloxycarbonylmethyl)-δ-valerolactone in the copolymer. When the benzyl-protecting groups were removed, the aliphatic polyesters bearing carboxylic groups were obtained. Moreover, the hydrophilicity of the polymer was improved. Thus, poly(ε-caprolactone-co-δ-valerolactone) might have great potential in biomedical fields. Copyright

Full text of DOI:10.1002/cjoc.201190088

FULL PAPER
Synthesis and Characterization of Poly(ε-caprolactone-co-δ-
valerolactone) with Pendant Carboxylic Functional Groups
Zeng, Yue(曾粤)
Zhang, Yan*(张琰)
Lang, Meidong*(郎美东)
Shanghai Key Laboratory of Advanced Polymeric Materials, Key Laboratory for Ultrafine Materials of Ministry of
Education, School of Materials Science and Engineering, East China University of Science and Technology,
Shanghai 200237, China
In this paper, aliphatic polyesters functionalized with pendant carboxylic groups were synthesized via several
steps. Firstly, substituted cyclic ketone, 2-(benzyloxycarbonyl methyl)cyclopentanone (BCP) was prepared through
the reaction of enamine with benzyl-2-bromoacetate, and subsequently converted into the relevant functionalized
δ-valerolactone derivative, 5-(benzyloxy carbonylmethyl)-δ-valerolactone (BVL) by the Baeyer-Villiger oxidation.
Secondly, the ring-opening polymerization of BVL with ε-caprolactone was carried out in bulk using stannous oc-
toate as the catalyst to produce poly(ε-caprolactone-co-δ-valerolactone) bearing the benzyl-protected carboxyl func-
tional groups [P(CL-co-BVL)]. Finally, the benzyl-protecting groups of P(CL-co-BVL) were effectively removed
by H using Pd/C as the catalyst to obtain poly(ε-caprolactone-co-δ-valerolactone) bearing pendant carboxylic acids
2
[P(CL-co-CVL)]. The structure and the properties of the polymer have been studied by Nuclear Magnetic Reso-
nance (NMR), Fourier Infrared Spectroscopy (FT-IR) and Differential Scan Calorimetry (DSC) etc. The NMR and
13
FT-IR results confirmed the polymer structure, and the C NMR spectra have clearly interpreted the sequence of
ε-caprolactone and 5-(benzyloxycarbonylmethyl)-δ-valerolactone in the copolymer. When the benzyl-protecting
groups were removed, the aliphatic polyesters bearing carboxylic groups were obtained. Moreover, the hydrophilic-
ity of the polymer was improved. Thus, poly(ε-caprolactone-co-δ-valerolactone) might have great potential in bio-
medical fields.
Keywords ε-caprolactone, δ-valerolactone, poly(ε-caprolactone-co-δ-valerolactone), pendant groups, ring-open-
ing polymerization
Introduction
Usually, these functionalized polyesters are often
synthesized by copolymerizing ε-caprolactone, lactide,
Aliphatic polyesters based on δ-valerolactone and
ε-caprolactone are of great interest for medical and
pharmaceutical applications because of their biocom-
or glycolide with a functionalized monomer that often
17,18
contains the protected functional groups.
The pro-
tected groups must be inert to the polymerization condi-
tions, but they should be removable under mild condi-
tions after polymerization, leaving the polymeric back-
bone intact. Ring-opening polymerization of the func-
tionalized dilactones was used to obtain the corre-
sponding polyesters which bore the hydrophilic pendant
groups after deprotection.
1-3
patible and biodegradable properties. However, the
degradation rate of poly(δ-valerolactone) (PVL) and
poly(ε-caprolactone) (PCL) is often slow. Moreover, the
simplicity of these polyesters presents limitations in
terms of functionality and physical properties, and in-
deed they are hydrophobic solids. The structural and
chemical modifications of the conventional aliphatic
polyesters materials have begun to be explored by many
researchers, such as the preparation of hyperbranched
The synthesis of the substituted lactone monomers is
the key to produce the functionalized polyesters. Langer
13
et al. first reported a new monomer prepared from
4,5
6-10
polyesters,
end-functionalized polyesters
11,12
and
alanine as early as 1993 that contained a protected
amino group and could polymerize by the same mecha-
nism as the monomer used for PLA synthesis. So far,
amino acids have been of the important originality to
chain-substituted polyesters.
Thereinto, the func-
tionalized polyesters with the pendant groups are par-
ticularly of increasing interest because the lateral func-
tional groups will be beneficial to the further chemical
and biological modification, and construction of the new
synthesize
the
functionalized
lactone
mono-
13,14,19-24
mers.
4-Substituted ε-caprolactones were also
13-16
biomaterials.
*
E-mail: zhang_yan@ecust.edu.cn; mdlang@ecust.edu.cn; Tel./Fax: 0086-021-64253916
Received October 23 2010; revised and accepted November 30, 2010.
Project supported by the National Natural Science Foundation of China (No. 20804015), the Fundamental Research Funds for the Central Universi-
ties (Nos. WD0913008, WD1014036), Specialized Research Fund for the Doctoral Program of Higher Education (No. 200802511021), Shanghai
Key Laboratory Project (No. 08DZ2230500) and Program for Changjiang Scholars and Innovative Research Team in University (No. IRT0825).
Chin. J. Chem. 2011, 29, 343— 350
© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
343

Zeng, Zhang & Lang
FULL PAPER
prepared by the Baeyer-Villiger oxidation of
1,4-cyclohexanedione, 1,4-cyclohexanedione mono-
g, 0.039 mol) and chloroform (150 mL) were added into
a flask and stirred until the solid was completely dis-
solved. Subsequently, BCP (6.96 g, 0.03 mol) were
added dropwise over a period of 1 h at 0 ℃ by external
cooling, and the reaction mixture was stirred at room
temperature for another 48 h. The solution was then
washed with a saturated solution of sodium thiosulfate
for three times, a saturated solution of sodium bicarbon-
ate for three times and a saturated sodium chloride solu-
tion for one time, respectively. After drying over anhy-
drous magnesium sulfate, the solvent was removed un-
der reduced pressure. The crude product was purified by
column chromatography on silica gel using ethyl ace-
tate/petroleum ether (1/4, V/V) as the eluent to obtain
the colorless unctuous BVL. The yield was 60%.
ethylene acetal, and the 1,4-cyclohexanediol deriva-
24-31
tives.
However, a few synthetic strategies of
α-substituted ε-caprolactones have attracted great inter-
32,33
est.
In the present paper, we explored one synthetic
strategy of aliphatic polyesters functionalized with the
pendant carboxylic groups through the ring-opening
polymerization of the novel functionalized lactone BVL
[5-(benzyloxy carbonylmethyl)-δ-valerolactone]. The
pendant carboxylic group would improve the hydro-
philicity and bio-affinity of the aliphatic polyesters, and
facilitate a variety of potential applications of the poly-
ester in controlled drug delivery and tissue engineering.
Synthesis of P(CL-co-BVL)
Experimental
The ring-opening polymerization of BCP and
ε-caprolactone (CL) was carried out in the polymeriza-
tion tube using stannous octoate as the catalyst (weight
ratio: 0.5‰). Exhausted-refilled with dry argon repeat-
edly for several times, the polymerization tube was
sealed in vacuum and placed in an oil bath at 150 ℃
for 60 h. After cooled to room temperature, the resulted
product was dissolved in CHCl3. The solution was
added dropwise into the excess petroleum ether to pre-
cipitate. The obtained P(CL-co-BVL) was washed with
methanol for three times to remove the residual mono-
mers and dried over phosphoric pentoxide in vacuum at
room temperature until constant weight.
Materials
ε-Caprolactone (ε-CL, Aldrich) was dried over CaH2
for 3 d and distilled under reduced pressure prior to use.
3-Chloroperoxybenzoic acid (MCPBA, Aldrich), Stan-
nous octate [Sn(II)Oct, Aldrich], benzyl-2-bromoacetate
(Chinese Chemical Reagent Co.), and 10% of palla-
dium/carbon (10% of Pd/C, Chinese Chemical Reagent
Co.) were used as received. Toluene (Shanghai Chemi-
cal Reagent Co.) and tetrahydrofuran (THF, Shanghai
Chemical Reagent Co.) were purified by refluxing over
a benzophenone-Na complex and distilling under nitro-
gen prior to use. Cyclopentanone (Shanghai Chemical
Reagent Co.) was distilled under reduced pressure be-
fore use. All of the other reagents were purchased from
Shanghai Chemical Reagent Co. and used without fur-
ther purification.
Deprotection of P(CL-co-BVL) to produce P(CL-co-
CVL)
P(CL-co-BVL) (0.90 g) were completely dissolved
in anhydrous tetrahydrofuran (40 mL) and then 10%
Pd/C catalyst (0.50 g) were added. After being purged
with argon for three times, the reaction mixture was
bubbled with hydrogen gas and stirred vigorously at
room temperature for 30 h. After the removal of the
Pd/C powder, the solution was dropped into excess pe-
troleum ether to obtain the final copolymer P(CL-co-
CVL). The degree of benzyl group removal was 100%.
Synthesis of BCP
Synthesis of enamine (1): Cyclopentanone (84.0 g, 1
mol), morpholine (130.0 g, 1.5 mol) and tolu-
ene-p-sulfonic acid (0.20 g, 1.16 mmol) were refluxed
in toluene (200 mL) at 140 ℃ for 48 h. The enamine
was collected by distillation under reduced pressure.
The conversion of cyclopentanone was about 70%.
Enamine (1) (45.9 g, 0.3 mol), methanol (50 mL)
and benzyl-2-bromoacetate (57.3 g, 0.3 mol) were in
turn added into a 250 mL two-necked flask and were
refluxed at 75 ℃ for 2 h. After evaporating the
methanol under reduced pressure, 60 mL of deionized
water was added into the reaction mixture and continu-
ously stirred at 70 ℃ for another 1.5 h, and then ex-
tracted with diethyl ether (60 mL) for three times and
dried with anhydrous sodium sulfate over night. After
distilling the solvent, the product was purified by col-
umn chromatography on silica gel using ethyl ace-
tate/petroleum ether (1/4, V/V) as the eluent to give the
colorless oil. The yield was 53%.
Characterization
The NMR spectra were recorded on Bruker
1
13
AVANCE 500 spectrometer in CDCl3. H NMR and C
NMR measurements were made at frequencies of 500
and 125 MHZ, respectively, and calibrated with respect
to the solvent signal with tetramethylsilane as standard.
FT-IR spectra were recorded on films or KBr pellets by
Nicolet FT-IR spectrometer (Magna-IR 550). SEC
measurements were carried out with tetrahydrofuran
(THF) as the eluent (1.0 mL/min) with a Water 2414
5
5
HPLC pump, three Ultrastyragel columns (2×10 , 10 ,
4
and 5×10 Å) in series, and refractive index detector.
The sample concentration was 5—10 mg/mL of THF.
The columns were calibrated with polystyrene standards
with a narrow molecular weight distribution. The ther-
Synthesis of BVL
MCPBA (6.7 g, 0.039 mol), sodium bicarbonate (3.2
344
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© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2011, 29, 343— 350

Poly(ε-caprolactone-co-δ-valerolactone) with Pendant Carboxylic Functional Groups
mal behavior of the polymers was studied by means of
differential scanning calorimetry (DSC) with
Baeyer-Villiger oxidation reaction using 3-chloroper-
1
oxybenzoic acid (MCPBA) as the oxidant. The H and
13
C peaks of BVL [Figures 1(b) and 2(b)] can be as-
a
DSC2910 Modulated DSC system. The specimens were
heated in sealed aluminum pans and scanned from
－100 to 200 ℃. First cooled to －100 ℃, and finally
heated to 200 ℃ using heating and cooling rates of 10
℃/min. All experiments were done under a flow of dry
N2. The wettability of the polymer film was assessed by
the JC200A contact angle measuring instrument. Drop-
lets of distilled water (10 µL) were deposited with a mi-
crosyringe onto the polymer surface, and the static con-
tact angle was measured. All the reported data were the
average of five measurements collected from different
areas of the coated surface.
1
13
signed easily by comparison with the H and C NMR
1
spectra of BCP. H NMR (CDCl3, 500 MHz) δ: 1.60
and 2.05 (2H, c,c', CH2CH2CH), 1.90 (2H, b,
CH2CH2CH2), 2.45 and 2.85 (2H, e,e', CHCH2CO),
2.65 (2H, a, COCH2CH2), 4.50 (H, d, CH) , 5.2 (2H, f,
13
CH2C6H5), 7.35 (5H, g, C6H5); C NMR (CDCl3, 125
MHz) δ: 18.80 (b, CH2CH2CH2), 27.91 (a, COCH2CH2),
29.72 (c, CH2CH2CH), 41.07 (e, CHCH2CO), 67.21 (f,
COCH2CH2), 76.83 (d, CH), 128.80, 128.89, 129.12,
136.04 (g, C6H5), 170.07 (h, CH2COOCH2), 171.41 (i,
CH2COOCH). NMR spectra indicated that the oxidation
of BCP by MCPBA was performed in the perfect re-
gioselectivity that only resulted in BVL (Scheme 1).
2-(Benzyloxycarbonylmethyl)-δ-valerolactone was not
Results and discussion
The synthesis of P(CL-co-CVL) was performed
through the reaction steps as shown in Scheme 1, in-
cluding the preparation of the substituted cyclic ketone
2-(benzyloxycarbonylmethyl)cyclopentanone
(BCP),
the synthesis of the functionalized lactone 5-(benzyl-
oxycarbonylmethyl)-δ-valerolactone (BVL), the polym-
erization of BVL with ε-caprolactone to produce the
random copolymer P(CL-co-BVL) and the benzyl de-
protection of P(CL-co-BVL) to obtain the desired
P(CL-co-CVL).
Synthesis of the new lactone monomer
Firstly, the novel α-substituted cyclopentanone BCP
was synthesized by the reaction of enamine with ben-
zyl-2-bromoacetate. As shown in Figures 1(a) and 2(a),
1
H NMR (CDCl3, 500 MHz) δ: 1.75 and 2.30 (2H, c,
CH2CH2CH), 1.60 and 2.10 (2H, b, CH2CH2CH), 2.00
and 2.30 (2H, a, COCH2CH2), 2.45 and 2.75 (2H, e,
CHCH2CO), 2.45 (H, d, CH), 5.15 (2H, f, CH2C6H5),
13
7.35 (5H, g, C6H5); C NMR (CDCl3, 125 MHz) δ:
21.05 (b, CH2CH2CH2), 29.73 (c, CH2CH2CH), 34.45 (e,
CHCH2CO), 37.82 (a, COCH2CH2), 46.04 (d, CH),
66.89 (f, COCH2CH2), 128.66, 128.71, 129.02, 136.30
(g, C6H5), 172.34 (h, CH2COOCH2), 219.30 (i,
CH2COCH).
1
Figure 1 Typical H NMR spectra of (a) BCP and (b) BVL.
BCP was subsequently converted into BVL by the
Scheme 1 Synthetic route of poly(ε-caprolactone-co-δ-valerolactone) bearing pendant carboxylic groups
O
O
p-CH PhSO H
3 3
BrCH CO CH C H
2 2 2 6 5
MCPBA
O
C H
6 5
N
O
O
NH
+
O
1
BCP
O
O
O
O
C H
6 5
ε-Caprolactone
O
O
O
O
O
O
Sn(Oct)
n
1
2
O
C H
6 5
O
CH CO CH C H
2 2 2 6 5
P(CL-co-BVL)
2
BVL
O
Pd/C H
2
O
O
n
1
O
CH CO H
2 2
P(CL-co-CVL)
Chin. J. Chem. 2011, 29, 343— 350
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345

Zeng, Zhang & Lang
FULL PAPER
ε-caprolactone (CL) can be easily homopolymerized,
and δ-valerolactone (VL) represents a “middle ground”
between BL and CL. When the hydrogen of 5-position
of VL was substituted by benzyloxycarbonylmethyl, the
ring-opening polymerization became much more diffi-
cult. Only few of BVL was converted into its ho-
mopolymer with low molecular weight although lots of
different polymerization conditions were tried. However,
the copolymerization of BVL with CL was carried out
successfully to produce the copolymers P(CL-co-BVL)
under the same polymerization condition. As shown in
Table 1, the actual molar fraction of BVL unit in the
copolymer was lower than that in the comonomer feed.
With increasing the amount of BVL monomers in the
feed, both the molecular weight and the yield of co-
polymer decreased. This may be due to the lower reac-
tivity of BVL as compared with CL and the steric hin-
drance of 5-benzyloxycarbonylmethyl functional
groups.
1
13
The
H
NMR and
C
NMR spectra of
P(CL-co-BVL) are shown in Figures 3(a) and 4(a). By
13
1
comparison with H and
C NMR spectra of
1
13
P(CL-b-VL), each group of peaks in H and C spectra
of P(CL-co-BVL) were assigned in the corresponding
39 1
figures. H NMR (CDCl3, 500 MHz) δ: 2.25 and 2.62
(2H, e,e', CHCH2CO), 2.30 (4H, a＋h, COCH2CH2),
13
Figure 2 Typical C NMR spectra of (a) BCP and (b) BVL.
5.10 (1H, d, CH), 5.25 (2H, f, CH2C6H5), 7.35 (5H, d,
13
C6H5); C NMR (CDCl3, 125 MHz) δ: 18.79 and 20.95
found, which was much different from the reported
oxidation of α-chlorocyclohexanone by MCPBA that
results in a mixture of two isomeric lactones
(b,b', CH2CH2CH2), 25.16 (p, CH2CH2CH2), 25.98 (j,
CH2CH2CH2), 28.80 (k, CH2CH2CH2), 29.67, 34.12
(a,a', COCH2), 33.78 and 27.92 (c,c', CH2CH2CH),
34.56 (m, COCH2CH2), 39.57 and 41.02 (e',e,
COCH2CH), 65.21 (l, COCH2CH2), 66.58 and 66.93
(f',f, CH2C6H5), 70.25 (d, CH), 128.66—136.49 (g,
C6H5), 170.50 (h, CH2COOCH), 173.20 (i, CO), 173.98
(n, CO). Figure 5(a) shows the typical spectra of
34
(α-Cl-ε-CL/ε-Cl-ε-CL) in a 95/5 molar ratio.
Synthesis of poly(CL-co-CVL)
The structure and properties of poly(CL-co-BVL)
The ability of the ring-opening polymerization de-
35-37
pended critically on the ring size of the monomer.
In
P(CL-co-BVL): 1730 (υC O), 1180 (υC
＝
Cas), 1046
—
—
O
－
1
), 733, 704 (δ CH) cm .
the case of polyesters prepared from lactones, the par-
ticular lactone used affected not only the polymerization
(υC
—
—
＝
O
Cs
Sequence analysis The properties are closely re-
rate but the thermal and degradation properties of the
38
lated to the sequence distribution of the two components
1 13
in the copolymers. Both H NMR and C NMR spectra
polymer.
γ-butyrolactone (BL) was very difficult to homopoly-
merize under most of the conditions, whereas
On the basis of the ring stability,
are considered in the sequence analysis of P(CL-co-
13
BVL). C NMR spectrum has been proved to be an
Table 1 Molecular characteristics and properties of poly(CL-co-BVL)
Conversion/%
Poly dispersity
－
a
a
c
4
Yield/% Mn /10 Mw /10
c
4
d
d
1
d
Entry
fV
XV
Tm /℃ ∆Ha /(J•g ) Tg /℃
b
b
(Mw/Mn)
BVL
CL
P(CL-co-BVL)-1 0.111 0.048
P(CL-co-BVL)-2 0.143 0.048
P(CL-co-BVL)-3 0.200 0.064
P(CL-co-BVL)-4 0.333 0.091
P(CL-co-BVL)-5 0.500 0.132
34.0
24.5
21.7
13.2
8.2
84.1
82.6
79.2
65.7
53.6
78.6
74.2
67.7
48.2
30.9
1.58
1.35
1.31
1.13
1.13
2.84
2.50
2.18
1.84
1.7.
1.80
1.85
1.67
1.62
1.54
53.7
52.0
51.6
48.7
45.0
86.1
71.3
70.7
69.9
61.8
－56.5
－51.6
－49.1
－48.0
－44.9
a
1
fV is the molar fraction of BVL in the comonomer feed; XV is the molar fraction of BVL in the copolymer, and calculated by H NMR
b
1
c
integration according to the benzyl signal at δ of about 7.4—7.5. Measured by H NMR spectrum (CDCl3). Determined by SEC in THF
d
using polystyrene as calibration standard. The melting points Tm, heat of fusion ∆Hm and glass transition temperature Tg were measured
by the first scan at a heating rate of 10 ℃/min.
346
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Chin. J. Chem. 2011, 29, 343— 350

Poly(ε-caprolactone-co-δ-valerolactone) with Pendant Carboxylic Functional Groups
1
Figure 3 Typical H NMR spectra of (a) P(CL-co-BVL)-3 and
(b) P(CL-co-CVL)-3.
13
Figure 4 Typical C NMR spectra of (a) P(CL-co-BVL)-3 and
more effective method in the sequence analysis of poly-
24,27,40
1
esters, while H NMR spectrum was seldom used.
13
(b) P(CL-co-CVL)-3.
The expanded C NMR spectrum of the P(CL-co-
BVL) is shown in Figure 6. CL and BVL units in co-
polymer were abbreviated with C and V, respectively.
The methylene carbon signals of j—j''', p—p''', m—m'''
of the central C units in the sequences C-C-C, V-C-C,
C-C-V, V-C-V were assigned as follows. Peaks j, p, and
m can be easily assigned to the C-C-C sequence by
comparison with the corresponding methylene carbon
39
signals in PCL. It was found that the smaller the mole
fraction of the BVL was in the copolymer, the weaker
the signals of j''', p''' and m''' were. So the signals of j''',
p''' and m''' can be assigned to the V-C-V sequence. It
will cause a larger upshift of these methylene carbons
that replacing a C unit by a V unit at the side of the
carbonyl group than at the other side of the central
39
ε-oxycaproyl unit (C). According to this, peaks j', p',
Figure 5 FT-IR spectra of (a) P(CL-co-BVL)-3 and (b)
P(CL-co-CVL)-3.
m' and peaks j'', p'', m'' were assigned to the sequences
of V-C-C and C-C-V, respectively. Figure 6 also indi-
cates that Cn, Cl and Ck only show diad sensitivity.
13
Compared with the data from C NMR spectrum of
41
39
13
Compared with the data from C NMR spectrum of
PVL and PCL-b-PVL, and considering the low mo-
lar fraction of BVL in copolymer, the low intensity peak
groups of a, b, c, d, e, h, f and i are assigned to the V-V
sequence, a', b' and i' are assigned to V-C sequence, c',
d', e', h', and f' are assigned to C-V sequence.
PCL, peaks n, k and l were assigned to the C-C-C se-
quence. Furthermore, peak n' was signed to C-V dyad, l'
and k' were assigned to the V-C dyad, because their
signal intensities increased when XV was raised.
All the peak assignments of the copolymer P(CL-co-
13
BVL)-3 in the C NMR spectrum were summarized in
When V was considered as the central unit, all the
carbon signals of it show diad sensitivity (Figure 6).
Table 2. The average length of homogenous C block
Chin. J. Chem. 2011, 29, 343— 350
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347

Zeng, Zhang & Lang
FULL PAPER
13
Figure 6 Expanded C NMR spectrum (CDCl3) of P(CL-co-BVL)-3. C and V represent CL unit and BVL unit, respectively.
Table 2 Average length of C blocks (LC) and V blocks (LV)
Carbon atoms in C block LC Carbon atoms in V block LV
age lengths were shown in Table 3. It was found that the
data of LC and LV of P(CL-co-BVL)-3 calculated from
different carbon peaks have small error. The average LC
was 20.41 and LV was 1.45.
Cl
Cn
Cm
Cp
Cj
19.06
20.18
20.84
21.06
21.63
19.70
Ci
1.40
1.44
1.50
1.38
1.37
1.47
1.45
1.60
1.45
Ca
On the basis of the average block length, the mole
fraction of BVL (XV) in P(CL-co-BVL) can be calcu-
20
Cb
lated from the following equation:
Cc
L
V
Cd
X ＝
(3)
V
L ＋L
V
C
Ck
Ce
Ch
XV of P(CL-co-BVL)-3 calculated from LV according to
above equation was 0.066, which was in reasonable
1
agreement with 0.064 calculated from H NMR spec-
Cf
Avg of LC
20.41
Avg of LV
trum (Table 1). This result further confirmed the inter-
13
pretation of the C NMR spectra of poly(CL-co-BVL).
(LC) and V block (LV) were calculated by the following
24,27,40,42
equations:
The DSC results were summarized in Table 1. Both
the Tg and the heat of fusion values of the P(CL-co-
BVL)s tended to remarkably decrease with increase of
the BVL unit contents as a result of the disruption of
polymer crystallinity. However, the glass transition
temperatures of the product P(CL-co-BVL)s tended to
increase with the increase of their BVL unit contents.
These results indicated that the higher the BVL unit
content was, the lower the chain/segmental mobility
would be detected for copolyester P(CL-co-BVL).
Ij＋Ij'
Ij''＋Ij'''
Ik
Ip＋Ip'
Im＋Im'
LC＝
＋1＝
＋1＝
＋1＝
Ip''＋Ip'''
Im''＋Im'''
(1)
Il
In
＋1＝ ＋1＝ ＋1
Il'
Ik'
In'
Il
Ia
Ib
Ic
Id
L ＝ ＋1＝ ＋1＝ ＋1＝ ＋1＝ ＋1＝
V
Il'
Ia'
Ib'
Ic'
Id'
Debenzylation of P(CL-co-BVL) to produce
P(CL-co-CVL) The debenzylation of the pendant
benzyloxycarbonylmethyl groups of P(CL-co-BVL) was
performed by catalytic hydrogenolysis with H2 over
(2)
Ie
Ih
If
＋1＝ ＋1＝ ＋1
I represented the peak intensity. The results of the aver-
Ie'
Ih'
If'
348
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© 2011 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2011, 29, 343— 350

Poly(ε-caprolactone-co-δ-valerolactone) with Pendant Carboxylic Functional Groups
Conclusion
Pd/C (10%) as a catalyst in the solvent of anhydrous
tetrahydrofuran at room temperature over 30 h to pro-
duce the corresponding copolymer P(CL-co-CVL) with
The novel functionalized lactone monomer
5-(benzyloxycarbonylmethyl)-δ-valerolactone BVL has
been successfully synthesized, and copolymerized with
ε-caprolactone in bulk at wide range of mole fractions in
the feed initiated by Sn(Oct)2 to produce poly(ε-caprol-
actone-co-δ-valerolactone) containing the lateral ben-
zyl-protected carboxyl functional group. The average
molecular weight of P(CL-co-BVL) deceased with the
increase of the molar feed ratio of BVL/CL, while the
melting point (Tm) and the heat of fusion (∆Hm) de-
creased and the glass transition temperature (Tg) in-
1 13
pendant carboxyl groups. The H NMR, C NMR and
FT-IR of P(CL-co-CVL) were shown in Figures 3(b),
1
4(b) and 5(b). Compared with the H NMR spectrum of
the protected copolymer P(CL-co-BVL), the peaks
around δ 5.2 and 7.3 which were assigned to the hydro-
gen atoms of the benzylprotected groups (CH2 and Ar-H,
respectively) disappeared in the spectrum of the depro-
tected copolymer P(CL-co-CVL) after 30 h of hydro-
genation [Figure 3(b)]. No benzyl signals were detected
13
in the C NMR spectrum either [Figure 4(b)]. All of
13
creased. The C NMR interpretation and the sequence
these clearly demonstrated that the benzyl groups were
removed completely. The other effective evidence of
this deprotection method was the disappearance of the
analysis of the copolymer with the feed ratio of 0.25
showed a random sequence distribution for the compo-
sition of the copolymer.
－
1
δCH vibrations of benzyl group at 733 and 703 cm in
The deprotection method using Pd/C as catalyst was
proved to be effective to transform benzyl-protected
P(CL-co-BVL) into benzyl-deprotected P(CL-co-CVL)
bearing the lateral carboxyl group with little main-chain
cleavage. The melting point (Tm), the glass transition
temperature (Tg) and the hydrophilicity of the ben-
zyl-deprotected P(CL-co-CVL) bearing the lateral car-
boxylmethyl functional group were higher than those of
the benzyl-protected P(CL-co-BVL), however, the
crystallinity was reversed.
the FT-IR spectrum [Figure 5(b)]. In addition, the
－
1
—OH stretching band centered at 3444 cm
was
strengthened tremendously after hydrogenolysis due to
the formation of pendant —COOH groups. All of these
clearly demonstrate that the benzyl groups were re-
moved completely.
The debenzylation of the pendant groups sharply af-
fected the copolymer thermal properties. For example,
Tm of the benzyl-deprotected P(CL-co-CVL)-3 was
much higher than that of the benzyl-protected
P(CL-co-BVL)-3 (Table 3), and P(CL-co-CVL)-3 ex-
hibited a little higher glass transition temperature than
that of the corresponding P(CL-co-BVL)-3. However,
∆Hm of the benzyl-deprotected P(CL-co-CVL)-3 was
much lower than that of the benzyl-protected
P(CL-co-BVL)-3. It might be attributed to the two pos-
sible reasons: (i) a carboxylic side group with less steric
hindrance would be more energetically favorable for
accommodating a secondary CVL unit than the BVL
unit; (ii) an intermolecular interaction caused by the
possible intermolecular hydroxyl bond between two
neighboring hydroxyl and hydroxyl or carbonyl groups
can stabilize the aggregated solid crystalline structure
The presence of carboxylic acid pendant-groups in
the P(CL-co-CVL) is expected to improve the biode-
gradability and hydrophilicity of the copolymer. Mean-
while, the achieved copolymer architecture gives versa-
tility to further derivatization, such as the introduction
of some moiety such as RGD, biotin etc. through the
carboxylic acid pendant groups.
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Chin. J. Chem. 2011, 29, 343— 350