Synthesis and performances of poly(butylene-succinate) with enhanced viscosity and crystallization rate via introducing a small amount of diacetylene groups

Article abstract of DOI:10.1016/j.cclet.2016.10.014

A cross-linkable comonomer containing a diacetylene group, named dimethyl 4,4′-(buta-1,3-diyne-1,4-diyl)dibenzoate (DA) was synthesized and copolymerized with dimethyl succinate and 1,4-butanediol to prepare a series of slightly cross-linked PBS copolyesters (PBDASx). The chemical structure, crystallization and rheological behaviours of PBDASx were well investigated. Compared to neat PBS, PBDASx showed the greatly increased crystallization rate because of the promoting nucleation of the cross-linking domains, and the XRD results indicated that it had no influence on crystallization structure of PBS. The rheological behaviours indicate that PBDASx possessed higher viscosity than neat PBS even at high shear rate and temperature. PBDAS0.3 exhibited better comprehensive properties than neat PBS, which will widen applications of PBS.

Full text of DOI:10.1016/j.cclet.2016.10.014

G Model
CCLET 3849 1–5
Chinese Chemical Letters xxx (2016) xxx–xxx
Contents lists available at ScienceDirect
Chinese Chemical Letters
journal homepage: www.elsevier.com/locate/cclet
1
Original article
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Synthesis and performances of poly(butylene-succinate) with
enhanced viscosity and crystallization rate via introducing a small
amount of diacetylene groups
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Q1
*
*
Gui-Cheng Liu, Wen-Qiang Zhang, Xiu-Li Wang , Yu-Zhong Wang
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Center for Degradable and Flame-Retardant Polymeric Materials (ERCPM-MoE), College of Chemistry, State Key Laboratory of Polymer Materials Engineering,
National Engineering Laboratory of Eco-Friendly Polymeric Materials (Sichuan), Sichuan University, Chengdu 610064, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Received 6 June 2016
Received in revised form 13 September 2016
Accepted 19 September 2016
Available online xxx
Q2
A cross-linkable comonomer containing a diacetylene group, named dimethyl 4,40-(buta-1,3-diyne-1,4-
diyl)dibenzoate (DA) was synthesized and copolymerized with dimethyl succinate and 1,4-butanediol
to prepare a series of slightly cross-linked PBS copolyesters (PBDASx). The chemical structure,
crystallization and rheological behaviours of PBDASx were well investigated. Compared to neat PBS,
PBDASx showed the greatly increased crystallization rate because of the promoting nucleation of the
cross-linking domains, and the XRD results indicated that it had no influence on crystallization structure
of PBS. The rheological behaviours indicate that PBDASx possessed higher viscosity than neat PBS even at
high shear rate and temperature. PBDAS0.3 exhibited better comprehensive properties than neat PBS,
which will widen applications of PBS.
Keywords:
Poly(butylene succinate) (PBS)
Slightly cross-linking
Diacetylene group
Crystallization property
Rheological behaviour
ã 2016 Xiu-Li Wang, Yu-Zhong Wang. Chinese Chemical Society and Institute of Materia Medica, Chinese
Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.
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1. Introduction
synthesized. It was found that DA can partly cross-linked at the
melt polymerization temperature (Fig. S1 in Supporting informa-
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The comprehensive properties of poly(butylene succinate)
(PBS) are comparable to the conventional polypropylene and
polyethylene, and it is considered to be a promising bio-based
polymers [1,2]. However, its melt strength/viscosity and crystalli-
tion), and therefore a small amount of DA is copolymerized with 1,
4-butanediol, and dimethyl succinate to prepare PBS copolyesters.
It is expected that the slightly-cross-linking reaction caused by DA
will increase the melt strength/viscosity and the crystallization
rate of PBS.
zation rate are low, which lead to
a poor blow-molding
processability. A cross-linking of PBS should be an effective way
to address those issues [3–7]. The traditional cross-linking
modification is achieved by post-processing. Not only extra
equipment is needed, but also some gels are formed during
modification, which will influence the reprocessability and
biodegradability of PBS. If we make PBS slightly cross-linking at
the polycondensation stage instead of post-processing, the cross-
linking degree is so low as not to affect PBS further thermal
processing.
Diacetylene group is prone to cross-linking reaction under
UV-irradiation or at high temperature [8–10]. In this study, a
functional monomer containing a diacetylene group, dimethyl
4,40-(buta-1,3-diyne-1,4-diyl)dibenzoate (DA), was designed and
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2. Results and discussion
2.1. Rheological behaviour of PBDASx
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The dynamic rheological behaviours of neat PBS and PBDASx
were studied systematically. Fig. 1a shows the complex viscosity–
frequency curves. For neat PBS, it presented low complex viscosity
and acted as a Newtonian behaviour. For PBDASx, it still showed
Newtonian behaviour like neat PBS, illustrating slightly cross-
linking did not change its flowing type. But it can be seen obviously
that the complex viscosity of PBDASx increased significantly
compared to PBS, which was due to the formation of slightly cross-
linking network and an increase in molecular weight caused by the
cross-linking of DA.
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From the storage modulus G0-frequency and loss modulus
G00-frequency curves (shown in Fig. 1b and c), we can see that G0 of
PBDASx was higher than that of PBS, suggesting that the PBDASx
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* Corresponding authors.
E-mail addresses: xiuliwang1@163.com (X.-L. Wang), yzwang@scu.edu.cn
(Y.-Z. Wang).
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http://dx.doi.org/10.1016/j.cclet.2016.10.014
1001-8417/ã 2016 Xiu-Li Wang, Yu-Zhong Wang. Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V.
All rights reserved.
Please cite this article in press as: G.-C. Liu, et al., Synthesis and performances of poly(butylene-succinate) with enhanced viscosity and
crystallization rate via introducing a small amount of diacetylene groups, Chin. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.cclet.2016.10.014

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G.-C. Liu et al. / Chinese Chemical Letters xxx (2016) xxx–xxx
100000
10000
1000
100
100000
100000
10000
1000
100
(a)
(d)
PBS
(c)
(b)
PBS
PBDAS0.3
PBDAS0.4
PBDAS0.5
PBS
PBDAS0.3
PBDAS0.3
PBDAS0.4
PBDAS0.5
10000
PBDAS0.4
PBDAS0.5
1000
1000
100
10
1
10
PBS
100
PBDAS0.3
PBDAS0.4
PBDAS0.5
10
1
1
0.1
0.01
0.1
1
10
100
0.01
0.1
1
10
100
10
100
1000
10000
100000
0.01
0.1
1
10
100
Frequency (Hz)
Frequency (Hz)
Frequency (Hz)
Loss modulus G'' (Pa)
Fig. 1. Dynamic rheological (a) complex viscosities vs. frequency, (b) storage modulus G0 vs. frequency, (c) loss modulus G00 vs. frequency and (d) storage modulus G0 vs. loss
modulus G00 for neat PBS and PBDASx.
1000
1000
(a)
(b)
100
10
100
10
PBDAS0.3-130
PBS-130
PBDAS0.3-140
PBS-140
100
1000
100
1000
Shear rate (s-1
)
Shear rate ( )
s-1
Fig. 2. Capillary rheological shear viscosities vs. shear rate (a) at 130 ꢀC and (b) at 140 ꢀC for neat PBS and PBDAS0.3.
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have an improved elastic response. Meanwhile, PBDASx also kept
that of neat PBS, even at different cooling rates (Fig. S3b in
Supporting information). To make clear how diacetylene group
affects the crystallization process of PBDASx, isothermal crystalli-
zation processes were investigated at 94 ꢀC by DSC. Avrami
equation was used to analyse the isothermal crystallization
kinetics [14]:
higher G00 than neat PBS, demonstrating that copolyesters have an
enhanced molecular interaction and reduced chain mobility [11].
This phenomenon may owe to the formation of cross-linking
network at the polycondensation step, which can be demonstrated
in Fig. 1d. The curves of PBDASx shown in Fig. 1d were almost
superimposed and deviated with that of neat PBS, suggesting that
some microstructure change occurred in PBDASx [11–13]. From the
above rheological data we can make a conclusion that a small
amount of DA monomers cross-linked at the polycondensation
step, and some cross-linking networks formed at the same time.
The capillary rheological behaviours of the neat PBS and
PBDAS0.3 are shown in Fig. 2. We can see that PBDAS0.3 showed
higher shear viscosity at the whole shear region, and even at the
testing temperature up to 140 ꢀC, PBDAS0.3 still remained higher
shear viscosity than PBS. This demonstrated that with the
introduction of DA content, the melt viscosity of PBDASx was
improved due to the formation of cross-linking network, which
will benefit the blow molding processing in the future.
1 ꢁ Xt = exp(ꢁktn)
(1)
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The equation can be rewritten as:
log[ꢁln(1 ꢁ Xt)] = log k + n log t
(2)
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A plot of log[ꢁln(1 ꢁ Xt)] versus log t (shown in Fig. S3c in
Supporting information) gives a straight line from which both the
Avrami exponent and the rate constant could be determined. n is
the Avrami exponent, which denotes the nature of the nucleation
and growth process. By calculation, the n values of PBS and PBDASx
were 2.6, 2.2, 2.1 and 2.4, suggesting that the crystallization of the
neat PBS corresponded to a three dimensional growth with
heterogeneous nucleation, while the segments of PBDASx tended
to be gathered on a two dimensional axial axe because of the
decreased segment integrity and mobility caused by the cross-
linking, the copolyesters corresponded to a two dimensional growth
with heterogeneous nucleation. The half-time of crystallization
(t1/2) values of PBS and PBDASx were 14.7, 1.2, 1.4, and 2.6 min,
respectively, illustrating PBDASx crystallized faster than PBS.
It is well known that the crystallization process of the melting
polymer can be divided into two steps, nucleation and crystal
growth. We can reasonably suppose that the cross-linking and
rigid DA unit structure may prevent the segment motion to a
certain extent, and, therefore, the crystal growth because they
reduce the segment regularity of PBS chain. However, the
crystallization rate and temperature were not decreased, but
increased considerably. Therefore, the increase in crystallization
rate can only be ascribed to the improvement in nucleation
efficiency by the introduction of cross-linkable DA unit structure.
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2.2. Crystallization behaviour of PBDASx
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The crystallization behaviour of PBDASx was evaluated by DSC
(Fig. S3a in Supporting information). The detailed crystallization
data are summarized in Table 1. It can be observed clearly that the
crystallization temperatures (Tc) of PBDASx were much higher than
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Table 1
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Crystallization data of PBS and PBDASx.
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100
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102
103
104
105
Sample
Cooling
n
t1/2 (min)
NE
Tc (ꢀC)
DHc (J/g)
PBS
71.1
85.4
85.2
82.4
62.9
67.2
58.5
65.3
2.6
2.2
2.1
2.4
14.7
1.2
1.4
0
PBDAS0.3
PBDAS0.4
PBDAS0.5
29.9
29.4
23.6
2.6
Please cite this article in press as: G.-C. Liu, et al., Synthesis and performances of poly(butylene-succinate) with enhanced viscosity and
crystallization rate via introducing a small amount of diacetylene groups, Chin. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.cclet.2016.10.014

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Table 2
Mechanical properties of neat PBS and PBDASx.
Sample
Tensile strength (MPa)
Elongation at break (%)
Young’s modulus (MPa)
PBS
33.7 ꢃ 0.9
33.6 ꢃ 1.3
38.5 ꢃ 0.2
37.3 ꢃ 0.4
331 ꢃ 16
322 ꢃ 17
24 ꢃ 2
286 ꢃ 20
291 ꢃ 19
343 ꢃ 20
337 ꢃ 17
PBDAS0.3
PBDAS0.4
PBDAS0.5
25 ꢃ 1
106
107
108
139
140
To estimate the nucleating efficiency (NE) of PBDASx, the
following method put forward by Fillion et al. is used [15,16]
(Fig. S4 in Supporting information):
of DA content. To take all this into account, PBDAS0.3 was
considered to possess optimum comprehensive properties.
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3. Conclusions
TcNA ꢁ Tc
NE ¼
ꢂ 100
ð3Þ
Tc max ꢁ Tc
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In summary, a comonomer containing a diacetylene group (DA),
was synthesized and introduced into PBS main chains successfully
via melt polymerization to prepare a series of slightly cross-linked
PBS copolyesters (PBDASx). PBDASx had high molecular weights
and showed good solubility in chloroform. The cross-link points
could be regarded as crystal nucleus favouring crystallization, and
PBDASx copolyesters had higher Tc and faster crystallization rate
than neat PBS. PBDASx had higher melt viscosity than neat PBS due
to the formation of cross-linking network caused by introducing
DA into its polymer chains. PBDAS0.3 exhibited better compre-
hensive properties than neat PBS, which will widen applications of
PBS.
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The detailed NE values of PBDASx are given in Table 1. It was
found that cross-link points can be regarded as crystal nucleus in
the nucleation step [7,17], therefore, it is beneficial to high
nucleating efficiency (NE), which will lead to a higher crystalliza-
tion temperature and faster crystallization. At the same time, we
can see that the Tc of PBDASx decreased a little with the increase of
DA content, illustrated that more cross-linking networks would
inhibit the crystal growth. However, due to the very low cross-
linking content, PBDASx still kept higher crystallization tempera-
ture than the neat PBS.
Meanwhile, compared to PBS, the crystalline morphology
showed that the crystals for PBDASx were tiny and imperfect
(Fig. S5 in Supporting information). WAXD was used to investigate
the crystalline structure of PBS and PBDASx (Fig. S3d in Supporting
information). It was found that although cross-linking enhanced
the crystallization rate, it had no influence on the crystalline
structure of PBS.
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4. Experimental
4.1. Materials
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1,4-Butanediol (BDO, AR grade), and zinc acetate (Zn(OAc)2, AR
grade) were purchased from Kelong Chemical Corporation
(Chengdu, China). Dimethyl succinate (DSA, AR grade) was
purchased from Alfa Aesar Chemical Corporation (Tianjin, China).
Tetrabutyl titanate (TBT), used as a catalyst, was also provided by
Kelong Chemical Corporation, and dissolved in anhydrous toluene
to prepare 0.2 g/mL solution. Methyl 4-iodobenzoate (AR grade),
ethynyltrimethylsilane (AR grade), copper(I) iodide (CuI, AR grade)
and bis(triphenylphosphine)palladium(II) chloride (Pd(PPh3)2Cl2,
AR grade) were purchased from Yinuokai Chemical Corporation
(Beijing, China). Copper(I) chloride (CuCl, AR grade), dimethyl
sulfoxide (DMSO, AR grade), potassium carbonate (K2CO3, AR
grade), triethylamine (Et3N), tetrahydrofuran (THF), hydrochloric
acid (HCl), methanol and ethanol were purchased from Kelong
Chemical Corporation. DA monomer (described in Supporting
information) is synthesized according to the following synthetic
procedures (Scheme 1).
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2.3. Tensile properties of PBDASx
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The mechanical properties play an important role in the
application of materials, and the tensile properties of PBDASx are
provided in Table 2. We can see that the tensile strength of
PBDAS0.3 was close to neat PBS while the elongation at break
decreased slightly. The Young’s modulus increased with the
increase of DA content. This was ascribed to the cross-linking
network and the increased rigidity of copolyesters, which will
reduce the segment mobility. As a result, the elongation at break
decreased, and the tensile strength and Young’s modulus
increased. Although the introduction of DA content can improve
the melt viscosity and crystallization properties of PBDASx, the
segment regularity of copolyesters was reduced with the increase
Scheme 1. Synthetic routes of DA.
Please cite this article in press as: G.-C. Liu, et al., Synthesis and performances of poly(butylene-succinate) with enhanced viscosity and
crystallization rate via introducing a small amount of diacetylene groups, Chin. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.cclet.2016.10.014

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G.-C. Liu et al. / Chinese Chemical Letters xxx (2016) xxx–xxx
Scheme 2. Synthetic procedure of PBDASx copolyesters.
Table 3
Composition and molecular weight data of PBDASx copolyesters.
Sample
fa (mol%)
Molecular weight
(dL/g)
fDA
fDSA
[
h b
]
Mn ꢂ 104 (g/mol)
Mw ꢂ 104 (g/mol)
PDIc
c
c
PBS
0
100
99.7
99.6
99.5
0.81
0.97
0.88
0.95
7.4
8.4
7.6
7.5
16
26
23
28
2.2
3.0
3.0
3.8
PBDAS0.3
PBDAS0.4
PBDAS0.5
0.3
0.4
0.5
a
Molar fraction of diesters in the feed.
Intrinsic viscosity measured in chloroform at 30 ꢀC.
Obtained by GPC.
b
c
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174
199
200
4.2. Synthesis and characterizations of PBS copolyesters containing DA
(PBDASx)
the Program for Changjiang Scholars and Innovative Research
Teams in University of China (No. IRT1026).
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The copolyesters (PBDASx) containing DA were synthesized by a
two-step melt polymerization (esterification and polycondensa-
tion, shown in Scheme 2). In the abbreviations, x refers to the molar
percentage (mol%) of DA units relative to the total diesters. In the
first esterification step, diesters (the compositions of DSA and DA
mixtures are shown in Table 3) and BDO with the molar ratio of
1:1.06, as well as the transesterification catalyst Zn(OAc)2 (0.2 wt%)
were added into a three-necked round-bottom flask equipped with
mechanical stirrer, water separator, and nitrogen inlet pipe. The
reactor was heated to 175 ꢀC and maintained for 4 h, and then the
catalyst TBT (0.1 wt%) was added to the reaction system. The
polycondensation was carried out at 230 ꢀC for 6 h under the
vacuum of 20–70 Pa. All the characterizations were described in
Supporting information. 1H NMR spectra of PBDASx (shown in
Fig. S2) confirm that DA has been successfully introduced into PBS
main chains. PBDASx show good solubility in chloroform and their
intrinsic viscosities are in the range of 0.81–0.97 dL/g (Table 3). The
molecular weights can be determined by GPC, and the data are also
shown in Table 3. We can see that the Mw values of PBDASx are
greater than that of PBS, which all are higher than 23 ꢂ104 g/mol,
and their PDI values are also increased when DA is introduced.
Appendix A. Supplementary data
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Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.cclet.2016.10.014.
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Please cite this article in press as: G.-C. Liu, et al., Synthesis and performances of poly(butylene-succinate) with enhanced viscosity and
crystallization rate via introducing a small amount of diacetylene groups, Chin. Chem. Lett. (2016), http://dx.doi.org/10.1016/j.cclet.2016.10.014