A novel aromatic-aliphatic copolyester consisting of poly(1,4-dioxan-2one) and poly(ethylene-co-1,6-hexene terephthalate): Preparation, thermal, and mechanical properties

Article abstract of DOI:10.1002/pola.24056

A novel multiblock aromatic-aliphatic copolyester poly(ethylene-co-1,6- hexene terephthalate)-copoly(1,4-dioxan-2one) (PEHT-PPDO) was successfully synthesized via the chainextension reaction of dihydroxyl teminated poly(ethylene-cohexane terephthalate) (PEHT-OH) with dihydroxyl teminated poly(1,4-dioxan-2-one) (PPDO-OH) prepolymers, using toluene2,4-diisocyanate as a chain extender. To produce PEHT-OH prepolymer with an appropriate melting point which can match the reaction temperature of PEHT-OH prepolymer with PPDOOH prepolymer, 1,6-hexanediol was used to disturb the regularity of poly(ethylene terephthalate) segments. The chemical structures and molecular weights of PEHT-PPDO copolymers were characterized by ¹H NMR, FTIR, and GPC The DSC data showed that PPDO-OH segments were miscible well with PEHT-OH segments in amorphous state and that the crystallization of copolyester was predominantly contributed by PPDO segments. The TGA results indicated that the thermal stability of PEHT-PPDO was improved comparing with PPDO homopolymer. The novel aromatic-aliphatic copolyesters have good mechanical properties and could find applications in the field of biodegradable polymer materials.

Full text of DOI:10.1002/pola.24056

A Novel Aromatic–Aliphatic Copolyester Consisting of Poly(1,4-dioxan-2-
one) and Poly(ethylene-co-1,6-hexene terephthalate): Preparation,
Thermal, and Mechanical Properties
JIE GONG, XIAO-JIE LOU, WEN-DA LI, XIN-KE JING, HONG-BING CHEN, JIAN-BING ZENG, XIU-LI WANG, YU-ZHONG WANG
Center for Degradable and Flame-Retardant Polymeric Materials (ERCEPM-MoE), College of Chemistry, State Key Laboratory of
Polymer Materials Engineering, Sichuan University, Chengdu 610064, China
Received 23 February 2010; accepted 30 March 2010
DOI: 10.1002/pola.24056
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A novel multiblock aromatic–aliphatic copolyester
poly(ethylene-co-1,6-hexene terephthalate)-copoly(1,4-dioxan-2-
one) (PEHT-PPDO) was successfully synthesized via the chain-
extension reaction of dihydroxyl teminated poly(ethylene-co-
hexane terephthalate) (PEHT-OH) with dihydroxyl teminated
poly(1,4-dioxan-2-one) (PPDO-OH) prepolymers, using toluene-
2,4-diisocyanate as a chain extender. To produce PEHT-OH pre-
polymer with an appropriate melting point which can match
the reaction temperature of PEHT-OH prepolymer with PPDO-
OH prepolymer, 1,6-hexanediol was used to disturb the regu-
larity of poly(ethylene terephthalate) segments. The chemical
structures and molecular weights of PEHT-PPDO copolymers
were characterized by 1H NMR, FTIR, and GPC. The DSC data
showed that PPDO-OH segments were miscible well with
PEHT-OH segments in amorphous state and that the crystalliza-
tion of copolyester was predominantly contributed by PPDO
segments. The TGA results indicated that the thermal stability
of PEHT-PPDO was improved comparing with PPDO homopoly-
mer. The novel aromatic–aliphatic copolyesters have good me-
chanical properties and could find applications in the field of
C
V
biodegradable polymer materials.
2010 Wiley Periodicals,
Inc. J Polym Sci Part A: Polym Chem 48: 2828–2837, 2010
KEYWORDS: copolyester; copolymerization; synthesis
INTRODUCTION Aromatic polyesters, particularly poly(ethyl-
ene terephthalate) (PET), has found more and more applica-
tion in food packing and textile industry because of its excel-
lent thermal stability and high mechanical strength.1–3
Unfortunately, this polymer has resistance to microbial and
fungal attack and usually remains unaltered in the environ-
ment. On the contrary, most of the synthetic biodegradable
polymers are aliphatic polyesters, such as poly(lactic acid)
(PLA),4,5 poly(butylene succinate) (PBS),6,7 and poly(p-dioxa-
none) (PPDO).8,9 PPDO is an aliphatic polyether ester that
has attracted more and more attentions in the recent years
owning to its excellent biodegradability, biocompatibility, and
good mechanical properties.10,11 It is considered as a pro-
spective candidate not only for medical application but also
for universal application such as coatings, films, and molded
products.9,12
thesized successfully in which PBAT with 44 mol % adi-
pate component was already commercialized by BASF
R
company and with the trademark as EcoflexV. Besides,
PET-co-aliphatic polyester type multiblock copolyesters
also have been synthesized, such as poly(ethylene tereph-
thalate-co-butylene succinate),16 poly(ethylene terephtha-
late-co-e-caprolactone),17 and poly(ethylene terephthalate-
co-lactic acid) (PET-PLA).18–21 Compared with the other al-
iphatic polyester, PPDO not only has ester bond but also
has ether bond in their chemical structure which made it
have excellent flexibility. Combining PPDO with PET can
impart the copolymers with good biodegradability and
flexibility.
It is known that the onset decomposition temperature of
PPDO is much lower than that of PET, so PPDO would be
subjected to immediate thermal degradation if it were
reacted with the molten PET. The same problem also
appeared in the synthesis of PET-PLA copolyester. To avoid
this, some researchers had to polymerize the PET monomers
with PLA oligomers22,23 at a relatively low reaction tempera-
ture, which would restrict the reactivity of PET monomers,
or introduce aliphatic diol/acid component into the back-
bone of PET to get appropriate low melting point.18 How-
ever, the molecular weight of the resulting copolyesters
In recent years, considerable interest has been attracted
by the preparation and application of aliphatic–aromatic
copolymers, some of which even have been proved to
have good biodegradability when the aliphatic composition
was switched to a certain ratio. Aliphatic–aromatic random
copolymers such as poly(ethylene succinate-co-terephtha-
late),13 poly(butylene adipate-co-terephthalate) (PBAT),14
and poly(butylene succinate-co-terephthalate)15 were syn-
Correspondence to: X.-L. Wang (E-mail: xiuliwang1@163.com) or Y.-Z. Wang (E-mail: yzwang@scu.edu.cn)
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 2828–2837 (2010) 2010 Wiley Periodicals, Inc.
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synthesized via the above method was not very high. As we
know, the lower molecular weight would encumber the
application of the copolyester. An effective way to obtain
high-molecular-weight copolymer was the chain-extension
reaction, which has been widely used in the polyurethane
and polyester industry to link two or more macromolecules
to achieve high molecular weight.24,25 At present, there have
been few reports on the synthesis of the aliphatic–aromatic
copolyesters using chain-extension reaction. Du et al.’s
work26–28 revealed that the aliphatic–aromatic copolyester
with urethane bonds in the backbones still had good biode-
gradability. Therefore, we used toluene-2,4-diisocyanate
(TDI) as a chain extender to connect PET and PPDO units
into one polymer chain.
temperature, and the resulting PPDO-OH prepolymer was
reduced to small particles in a grinder. The obtained product
was dried in vacuum oven at 60 ꢀC for 48 h. The PPDO
homopolymer was prepared by chain extension reaction of
PPDO prepolymer, the synthetic method was followed by our
previous work.8
Synthesis of Dihydroxyl Terminated Poly(ethylene-co-
1,6-hexene terephthalate) (PEHT-OH) Prepolymers
Dihydroxyl teminated HO-PEHT-OH prepolymer was synthe-
sized via a two-step reaction, transesterification and polycon-
densation. At first, a predetermined molar ratio (DMT/EG ¼
1/2.2) of DMT and EG monomers with a catalyst, zinc ace-
tate (0.05 wt % amount of dimethyl terephthalate) were
added into a 250-mL single-necked round-bottomed flask
equipped with the mechanical stirrer. The mixture was
In this study, dihydroxyl terminated poly(ethylene-co-1,6-
hexene terephthalate) (PEHT-OH) prepolymer with suitable
melting point was synthesized by polymerization of ethylene
glycol, 1,6-hexanediol, and dimethyl terephthalate. Dihy-
droxyl terminated PPDO prepolymers were synthesized via
ring-opening polymerization of p-dioxanone monomer initi-
ated by 1,4-butanediol with stannous octoate as a catalyst.
Then, TDI was used as a chain extender to synthesize the
PEHT-PPDO copolyesters. The chemical structure, the ther-
mal stablility, the thermal transition behaviors, and the me-
chanical properties of the copolymer were well investigated.
As far as we know, this is the first report on the synthesis of
PET-PPDO copolymer using this method.
ꢀ
stirred at 175 C for 4 h under nitrogen, and the product of
transesterification reaction, bishyroxyethyl terephthalate, was
obtained. The water separator was used to collect the metha-
nol which was produced in the reaction so as to calculate
the yield. Then, bishyroxyhex terephthalate was also pre-
pared via the same transesterification procedure, and the
feed ratio of monomers and the mount of catalyst were the
same as in the preparetion of bishyroxyethyl terephthalate.
Second, PEHT-OH prepolymer was prepared by the conden-
sation polymerization of predetermined molar ratio of bish-
yroxyethyl terephthalate and bishyroxyhex terephthalate.
Bishyroxyethyl terephthalate and bishyroxyhex terephthalate
were mixed in a 500-mL three-necked round-bottomed flask,
and antimony trioxide (0.8 wt % amount of dimethyl tereph-
thalate) was added as a catalyst. Initially, the temperature of
the reaction mixture was gradually increased to 210 ꢀC and
kept for 1 h. Then, the system was heated to 250 ꢀC and
maintained for another 1 h. Furthermore, the vacuum was
gradually reduced to 60 Pa in 0.5 h, and the temperature
was increased to 280 ꢀC. About 1 h later, a viscous liquid
was produced, and then cooled down to the room tempera-
ture under nitrogen. The resulting product was purified by
dissolving in chloroform and then precipitating in excessive
methanol. The white powder ꢀproduct was dried to constant
weight in vacuum oven at 60 C for the further investigation.
EXPERIMENTAL
Materials
p-Dioxanone (PDO) was provided by the Center for Degrad-
able and Flame-Retardant Polymeric Materials (Chengdu,
China). The monomer was distilled under reduced pressure
until the purity was greater than 99.8% before use. Stannous
octoate (Sn(Oct)2) was purchased from Sigma (USA) and
used as received. Ethylene glycol (EG, AR grade) and 1,4-
butanediol (BD, AR grade) were received from Kelong Chem-
ical Corp. (Chengdu, China) and were used without futher
purification. Dimethyl terephthalate (DMT) was obtained
from Guoyao Chemical Plant (Chengdu, China). Toluene-2,4-
diisocyanate (TDI) (AR grade) obtained from Bodi Chemical
Plant (Tianjin, China) was used without further purification.
All the other chemicals with AR grades were used as
received.
Synthesis of PEHT-PPDO Copolyesters by
Chain-Extension Reaction
The chain-extension reaction was accomplished using a glass
reactor under nitrogen atmosphere. PPDO-OH and PEHT-OH
prepolymers were put into the reactor which was evacuated
and purged with nitrogen for three times, and then the reac-
Synthesis of Dihydroxyl Terminated Poly(1,4-dioxan-2-
one) (PPDO-OH) Prepolymers
ꢀ
Ring-opening polymerization of PDO was carried out in a
flame-dried glass reactor with the magnetic stirring. The re-
actor was dried and purged with nitrogen three times before
addition of PDO whose purity was more than 99.9%. 1,4-
Butanediol was injected bꢀy a syringe and the reactor was
heated in a oil bath at 80 C with stirring for 10 min. Then,
the catalyst SnOct2/toluene solution was introduced into the
flask with the molar ratio of 500:1 (PDO:SnOct2), and the
mixture was stirred for 48 h in nitrogen atmosphere. After
the reaction, the reactor was fast cooled down to the room
tor was immersed in a silicone oil bath at 150 C. When the
prepolymers were molten completely,
a predetermined
amount of TDI was injected into the reactor. The chain-
extension reaction proceeded for 1 h with a mechanical stir-
rer under nitrogen protection. After reaction, the reactor was
cooled down to the room temperature rapidly. The resulting
copolymers were also purified by dissolving in chloroform
and then precipitating in excessive methanol and then the
white ꢀpowder was dried to constant weight in vacuum oven
at 60 C for further investigation.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 The synthetic pro-
cesses of PPDO-OH (A) prepoly-
mer, PEHT (B) prepolymer and
PEHT-PPDO copolyester (C).
Intrinsic Viscosity
Gel Permeation Chromatography
The intrinsic viscosities of PPDO-OH, PEHT-OH, and PEHT-
PPDO were measured with an Ubbelohde viscometer at
30 ꢀC using phenol/1,1,2,2-tetrachloroethane (1/1, v/v) as
solvent.
The molecular weights and polydispersity of the polymers
were determined by gel permeation chromatography at 35
ꢀC with Waters instrument equipped with a 2414 refractive
index detector, a model 1515 pump, and a Waters model
717 autosampler. Chloroform was used as the eluant at a
flowing rate of 1.0 mL/min, and the sample concentration
was 2.5 mg/mL.
Fourier Transform Infrared Spectroscopy
Fourier transform infrared (FTIR) spectra of the samples
were recorded on a Fourier transform infrared spectrometer
in a range of wave numbers from 4000 to 300 cmꢁ1. The
specimens were milled into powders and then mixed and
laminated with KBr. The resolution and scanning time were
4 cmꢁ1 and 32 times, respectively.
Differential Scanning Calorimetry
Differential scanning calorimetry analysis was carried out on
a TA Instrument DSC-Q100. Samples were quickly heated to
160 ꢀC and kept for 5 min to remove thermal history, then
were cooled to ꢁ20 ꢀC at a rate of 10 ꢀC/min, and finally
ꢀ
were reheated to 160 C at the same rate.
Nuclear Magnetic Resonance Spectroscopy
Thermogravimetric Analysis
The chemical structures and compositions of the obtained
polymers were characterized by a Varian Inova 400 NMR
spectrometer at ambient temperature, using CDCl3 as the
corresponding solvent and tetramethylsilane as the internal
chemical shift standard.
Thermogravimetric analysis (TGA) was used to determine
the thermal stabilities of PPDO-OH, PEHT-OH, and PEHT-
PPDO. The thermograms were recorded from room tempera-
ture to 500 ꢀC at a heating rate of 10 ꢀC/min under N2
atmosphere on a TA Instruments TGA-Q500. The isothermal
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FIGURE
PPDO-OH.
1
1H NMR spectra of
stability of PEHT-PPDO was carried out to monitor the varia-
tion of intrinsic viscosity with time above its melting temper-
ature from which the degradation of PEHT-PPDO in process-
ing conditions could be simulated. The samples were put
3.81 ppm (dHd) were assigned to the three methylene of
PPDO, respectively. The signals occurring at 4.11 ppm (dHb)
and 1.74 ppm (dHa) were assigned to the methylene protons
0
of BD. Futhermore, the signals of 3.77 ppm (dHd ) and 3.75
0
ppm (dHe ) were assigned to the terminal methylene group of
ꢀ
into an isothermal oven at 120 C and taken out for intrinsic
viscosity testing for a given interval time.
PPDO-OH. The integral area ratio of dHb to dHa was about
1:1, demonstrated that BD was incorporated into the polymer
chain and PPDO had two terminal hydroxyl groups. The num-
ber-average molecular weight (Mn) of PPDO-OH prepolymers
could be determined according to the following equation:
Mechanical Properties
Tensile strength and elongation at break of PEHT-PPDOs
were tested on an Instron Universal Testing Machine (Model
4302, Instron Engineering Corp., Canton, MA) at crosshead
speed of 50 mm/min at room temperature. The samples
were prepared via hot pressing and cutting with a dumbbell-
shaped cutter. The thickness and width of samples were 0.5
mm and 4 mm, respectively. The length of the sample
between two pneumatic grips of testing machine was 20
mm. Each sample was tested for seven times, and the results
were averaged to gain a mean value.
MnPPDOꢁOH ¼ 2 ꢂ ½ðI3:81 þ I3:77Þ=I3:75ꢃ ꢂ 102 þ 90
(1)
where I3.81 and I3.77 were the intensity of the internal, and
terminal methylene groups of the PPDO-OH, respectively.
I3.75 was the intensity of the methylene groups which were
close to the terminal hydroxyl groups. The values 102 repre-
sented the molecular weight of the repeating units of PPDO,
and 90 was the molecular weight of BD.
RESULTS AND DISCUSSION
PEHT prepolymers were synthesized by ethylene glycol, 1,6-
hexanediol, and dimethyl terephthalate by two-step reac-
tions: transesterification and polycondensation [Scheme
1(B)]. The chemical structures and number-average molecu-
lar weights of PEHT prepolymers were characterized by 1H
NMR and shown in Figure 2. It can be seen in Figure 2 that
the component ratio of the 1,6-hexanediol segments in PEHT
prepolymers was higher than the feed ratio. The reason for
this was that the boiling point of EG (196–198 ꢀC) was
Characterization of the Synthesized PPDO-OH
and PEHT-OH
PPDO-OH was synthesized by ring-opening polymerization of
PDO with 1,4-butanediol (BD) as an initiator, using SnOct2 as
a catalyst [Scheme 1(A)]. The chemical structure and num-
ber-average molecular weights of PPDO-OH were character-
ized by 1H NMR spectra (shown in Fig. 1). We can see that
resonances located at 4.36 ppm (dHe), 4.21 ppm (dHc), and
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 2 1H NMR spectra of PEHT-OH.
much lower than that of HD (253–260 ꢀC), thus the former
was easier to be evaporated from the reaction system than
the latter during the condensation polymerization.
lar weight of resulting PEHT prepolymer was deduced
according to the following two equations:
Is þ It
1H NMR spectrum (Fig. 2) revealed the chemical structure
and number-average molecular weights of PEHT-OH. The
peak occurring at 4.70 ppm (dHf) could be assigned to meth-
ylene protons of the repeating AOCH2CH2OA units, and the
terminal methylene protons of AOCH2CH2OA units could be
observed at 3.98 ppm (dHk) and 4.50 ppm (dHj), respec-
tively. The signals at 8.08–8.11 ppm (dHs, dHt) could be rea-
sonably attributed to methine proton of the phenyl groups,
and these two peaks could not be obviously distinguished as
their chemical shifts were very close to each other. It was
found that the three different methylene protons of the
repeating AO(CH2)6OA units were observed at 4.35 ppm
(dHg), 1.82 ppm (dHh), and 1.59 ppm (dHi). Moreover, the
peaks at 4.35 ppm (dHp), 3.66 ppm (dHr), and 1.47 ppm
(dHq), belonging to the terminal methylene protons of
AO(CH2)6OA units based on the distance to the phenyl
groups, respectively. Therefore, the number average molecu-
DP ¼
(2)
ðIi þ IrÞ=2
If
Ih
Mn:PEHT ¼ DP ꢂ ð
ꢂ 62 þ
ꢂ 118 þ 166 ꢁ 18Þ
If þ Ih
If þ Ih
(3)
where Dp was the polymerization degree of PEHT prepoly-
mer, It and Is designated the peak intensities of methane pro-
tons of phenyl groups. Ij and Ir represented the peak
intensities of the terminal methylene protons of
AOCH2CH2OA and AO(CH2)6OA units, respectively. If and Ih
were the intensities of methylene protons of the repeating
AOCH2CH2OA and AO(CH2)6OA units; the proportion of
which could provide the molar ratio of ethylene glycol units
to 1,6-hexanediol units in PEHT prepolymers. The molecular
weights of ethylene glycol, 1,6-hexanediol, terephthalic acid,
and H2O were 62, 118, 166, and 18, respectively.
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FIGURE 3 1H NMR spectra of PEHT-PPDO copolyester.
Synthesis and Characterization of PEHT-PPDO
Copolyesters
2.19 (dHw) could be attributed to methyl protons of TDI, and
the phenyl protons of TDI units located at about 7.08 (dHz),
7.06 (dHu) and 6.72 (dHv). The composition of the copolyest-
ers was determined by 1H NMR, which could be calculated
according to the following equation:
PEHT-PPDO copolyesters were prepared through chain-
extension of PPDO-OH ꢀand PEHT-OH prepolymers in the
presence of TDI at 150 C for 1 h. The reaction process was
shown in Scheme 1(C). Based on our previous work,21 the
molar ratio of ANCO/AOH should be 1:1 to obtain the prod-
ucts with high molecular weight and the high efficiency of
the chain extension. Therefore, in this study, the molar ratio
of ANCO/AOH was fixed at 1:1.
PEHT=PPDOðmol=molÞ ¼ ½ðIs þ ItÞ=4ꢃ=ðId=2Þ
(4)
where It and Is designated the peak intensities of methane
protons of phenyl groups belonged to PEHT component, Id
was the intensity of the internal methylene groups of the
PPDO component.
The chemical structures of PEHT-PPDO were characterized
by FTIR and 1H NMR. The 1H NMR spectrum of the copo-
lyesters was shown in Figure 3. It was found that all the
characteristic signals ascribed to both repeated segments of
PPDO-OH (dHc, dHd) and PEHT-OH (dHf, dHg, dHh, dHi) pre-
The FTIR spectra of PEHT-OH, PPDO-OH prepolymers, and
PEHT-PPDO copolyester were illustrated in Figure 4. It
can be seen clearly that the characteristic absorptions of
PPDO-OH prepolymer such as 1736 cmꢁ1, 1533 cmꢁ1, and
1431 cmꢁ1, which belonged to the absorption of carbonyl
group, methylene and CAOAC stretching, respectively, were
found. OAH vibration at about 3500 cmꢁ1 assigning to both
prepolymers disappeared in PEHT-PPDO spectrum, which
polymers were presented in the spectrum of PEHT-PPDO.
0
Furthrermore, the signals which belonged to PPDO-OH (dHe ,
0
dHd ) and PEHT-OH (dHj, dHk, dHq, dHr) disappeared respec-
tively, indicating that all the terminal hydroxyl groups of pre-
polymers had thoroughly reacted. The peaks occurring at
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 4 FT-IR spectra of PEHT-OH, PPDO-OH, and PEHT-
PPDO copolymer.
FIGURE 5 GPC diagrams of PEHT-OH, PPDO-OH, and PEHT-
PPDO copolyesters.
demonstrated that the hydroxyl groups of the prepolymers
were consumed completely. The new peak at around 3350
cmꢁ1 attributed to NAH stretching vibration can be found,
meanwhile the ANCOA stretching at 2200 cmꢁ1 disap-
peared, all of which evidenced that TDI was thoroughly
reacted and the isocyanate groups had been changed to ure-
thane groups. It illustrated that the chain extension pro-
ceeded just as we expected and the ratio of ANCO/AOH we
chose was effective for the reaction.
tio of prepolymers kept growing. As we know, the reactivity of
hydroxyl groups of these prepolymers was different, when the
feed ratio of PEHT-OH to PPDO-OH was 75:25, the hydroxyl
groups in reaction system had the highest reactivity, which
made the chain-extension efficiency achieve the maximum.
The molecular weights of PEHT-OH, PPDO-OH prepolymers,
and PEHT-PPDO copolyester were determined by GPC
(shown in Fig. 5), and the detailed results were also listed in
Table 1. The GPC traces of PEHT-PPDO1 to PEHT-PPDO5
showed a single peak, demonstrated that a complete reaction
took place without unreacted prepolymers remaining.29 The
GPC results can prove that using NMR to calculate the
amount of chain extender TDI was a useful method in chain-
extension reaction. From Table 1, we can see that all co-
polyesters had higher molecular weights, indicated that the
chain-extension reaction was successfully achieved. Mean-
while, it could be found that the molecular weights of PEHT-
OH and PPDO-OH prepolymers calculated by NMR spectra
To investigate the effect of the chemical strucuture on the
properties of the copolyesters, PEHT-PPDOs with different
compositions had been synthesized, which was named as
PEHT-PPDO1–PEHT-PPDO5. The compostions of the obtained
copolymers were listed in Table 1. It can be seen from Table 1
that the intrinsic viscosity of PHET-PPDO copolymers
increased with the increasing feed weight ratio of PEHT-OH
and reached the maximum when the feed ratio of PEHT-OH to
PPDO-OH was 75:25 (PEHT-PPDO3). After that, the intrinsic
viscosity of PEHT-PPDO decreased gradually when the feed ra-
TABLE 1 The Composition and the Molecular Weights of PEHT-PLLA Copolyesters
Composition Ratio
Feed Ratio (wt %)
PEHT-OH PPDO-OH
(wt %)
Mn,NMR
Mn,GPC ꢂ10ꢁ4
Mw,GPC ꢂ10ꢁ4
[g]
Samplea
PEHT-OH PPDO-OH
(g/mol)
(g/mol)
(g/mol)
PDb
(dL/g)
PPDO-OH
100
–
–
–
–
6,353
8,181
0.78
0.82
4.96
5.75
7.87
6.94
5.96
1.45
1.91
1.86
2.33
2.88
2.76
3.94
3.45
2.42
0.33
0.38
0.81
0.90
1.10
0.80
0.70
PEHT-OH
100
–
–
c
PEHT-PPDO1
PEHT-PPDO2
PEHT-PPDO3
PEHT-PPDO4
PEHT-PPDO5
a
56.3
43.7
58.7
60.9
70.8
83.4
98.0
41.3
39.1
29.2
16.6
2.0
–
14.28
15.87
31.01
23.94
14.42
c
65.9
75.0
86.5
93.5
34.1
25.0
13.5
6.5
–
c
–
c
–
c
–
All samples are synthesized at 150 ꢀC for 1 h.
Polydispersity.
The molecular weight can not be calculated by 1H NMR.
b
c
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ARTICLE
tion temperature from 230 to 270 ꢀC belonged to the
decomposition of PPDO segments, and the second stage with
ꢀ
a maximum decomposition temperature of aroud 400 C was
due to the PEHT segments. From Table 1, we can find that
all PEHT-PPDO samples had a higher initial decomposition
temperature (T5%) and maximum decomposition tempera-
ture (Tmax1) than those of PPDO homopolymer, even though
PPDO homopolymer had much higher intrinsic viscosity ([g]
¼ 2.0 dL/g), demonstrated that all PEHT-PPDO copolyesters
have better thermal stability than PPDO homopolymer. It
was also be found from Table 1 that the values of T5% were
increased with the increase of PEHT content in the copo-
lyesters, but Tmax2 that was ascribed to the decompositon of
PEHT almost invaried with the composition. This demon-
strated that the presence of aromatic groups, which derived
from PEHT, can obviously reduce the unzipping depolymer-
ization of PPDO segments and eliminated to generate PDO
monomers.31
FIGURE 6 TG curves of PEHT-OH, PPDO, and PEHT-PPDO
copolyesters.
Thermal and Crystallization Behaviors of PEHT-PPDO
Copolyesters
were lower than those determined by GPC; this phenomenon
could be explained by the different characteristics of two
testing methods.30 The molecular weight distribution of
PEHT-PPDO copolyesters were a little broader than that of
prepolymers, which could ascribed to the fast reaction rate
and the difficult controllability of the chain extension. It
could be observed that the polydispersity of PEHT-PPDO3
was the broadest of five PEHT-PPDO samples, which can be
ascribed reasonably to its high molecular weight.
The DSC cooling and heating scans of PEHT-OH, PPDO-OH,
and PEHT-PPDO with different weight ratios were shown in
Figures 7 and 8, respectively. The relevant data determined
from Figure 7 and Figure 8 were summarized in Table 2. No
crystallization peak could be detected in the cooling scans
for all the samples due to their slow crystallization rate, and
only glass transition temperatures could be observed from
their cooling scans. However, in the heating scans, all the
samples showed the obvious melting point, indicated that
the copolyesters were semicrystallization polymer.
Themal Stability of PEHT-PPDO Copolyesters
The thermal stabilities of PEHT-PPDO were studied by TGA.
The TG curves of PEHT-OH prepolymer, PPDO homopolymer,
and PEHT-PPDO were shown in Figure 6, and the relevant
thermal decomposition temperatures were summarized in
Table 2. There was no residue left for PEHT-OH prepolymer
When PEHT content was low, such as PEHT-PPDO1ꢄ 3, the
cold crystallization exothermal peaks could be detected, and
it became wider and weaker with the increase of PEHT con-
tent. For PEHT-PPDO4 and PEHT-PPDO5, we can not find the
cold crystallization exothermal peaks. As we know, the crys-
talizability of PPDO segment was better than that of PEHT
due to its chain regularity. So, the decrease of PPDO content
would decrease the crystalizability and the crystallization
rate of the copolyesters. Beside this, the introduction of TDI
ꢀ
and only 0.2wt % residue for PPDO homopolymer at 500 C.
At the same time, the residue of PEHT-PPDO1 to PEHT-
PPDO5 copolyesters ranged from 2.18 to 3.93%. It can be
found that the PEHT-PPDO curves included two thermal deg-
radation stages. The first stage with a maximum decomposi-
TABLE 2 The Thermal Degradability and Thermal Transition Data of PEHT-OH, PPDO, and PEHT-PPDO Copolyesters
Tm (ꢀC) Td (ꢀC)
a
b
c
d
Sample
Tg1 (ꢀC)
Tg2 (ꢀC)
Tc (ꢀC)
DHc (J/g)
Tm1
Tm2
DHm (J/g)
T5%
Tmax1
Tmax2
PEHT-OH
PPDO
–
15.7
–
72.6
44.0
54.6
66.3
67.7
–
33.2
54.8
32.0
3.0
14.4
–
105.9
101.4
99.6
99.3
99.4
99.5
–
117.1
–
21.8
64.2
37.3
12.0
24.6
8.2
364.1
194
–
399.1
–
ꢁ9.3
ꢁ7.9
ꢁ6.6
ꢁ6.4
ꢁ5.7
–
234.3
245.3
250.0
275.5
269.2
272.1
PEHT-PPDO1
PEHT-PPDO2
PEHT-PPDO3
PEHT-PPDO4
PEHT-PPDO5
a
19.7
22.0
24.6
24.5
29.8
117.6
117.7
119.2
117.1
117.2
224.1
233.7
258.4
260.2
272.8
400.1
400.2
400.5
400.2
400.2
–
–
7.3
d
DHm concluded the progress of Tm1 and Tm2.
Decomposition temperature of polymers at weight loss of 5%.
The maximum-decomposition-rate temperature in the first stage
The maximum-decomposition-temperature in the second stage (PEHT
segment).
b
c
(PPDO segment).
NOVEL AROMATIC–ALIPHATIC COPOLYESTER, GONG ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TABLE 3 The Mechanical Properties of PEHT-PPDO
Copolyesters
Tensile
Elongation
Sample
Strength (MPa)
at Break (%)
PEHT-PPDO 1
PEHT-PPDO 2
PEHT-PPDO 3
PEHT-PPDO 4
PEHT-PPDO 5
31.4 6 1.2
36.0 6 0.6
36.9 6 2.4
38.0 6 0.8
40.2 6 1.7
417.1 6 34
302.4 6 23
364.3 6 16
318.9 6 9
332.6 6 28
Mechanical Properties
Mechanical properties of polymers are extremely important
for potential applications. In this study, the tensile properties
of the copolyesters have been investigated and the results
were listed in Table 3. It was found that the tensile strength
of the copolymers increased with the increase of PEHT com-
ponent, which should be ascribed to the gradual increase of
aromatic segment content. For PEHT-PPDO1, the content of
aliphatic and aromatic segments was approximately the
same, which resulted in the minimal tensile strength and
maximal elongation at break. When the PEHT content further
increased, however, the elongation at break decreased, but
its decrease extent had no direct relationship with their
PEHT content. PEHT-PPDO3, which had the maximal molecu-
lar weight, had a higher elongation at break than the other
samples, but it was still lower than that of PEHT-PPDO1.
FIGURE 7 DSC cooling scans of PEHT-OH, PPDO-OH, and
PEHT-PPDO copolyesters.
further disturbed the regularity and flexibility of copolyester
chains. The above reasons made the crystalline enthalpy
(DHc) and the melting enthalpy (DHm) decreased gradually
with the increase of PEHT content.
From Table 2, it can be seen that there were two glass tran-
sition temperatues and melting points for PEHT-PPDO1ꢄ 3.
For example, PEHT-PPDO1 presented an obvious glass transi-
tion temperature (ꢁ7.9 ꢀC) which was close to the Tg of
PPDO (ꢁ9.3 ꢀC) and an inconspicuous Tg at 19.7 ꢀC which
was approached Tg of PEHT. With the increase of PEHT con-
tent, PEHT made main contribution to the Tgs and Tms of the
copolyesters, and finally it made PEHT-PPDO4 and PEHT-
PPDO5 have only one Tg and Tm close to those of PEHT.
From Table 2, it can be found that PEHT-PPDO3 had the
highest Tm2 of the five copolymer samples, which may be
due to its the highest molecular weight.
CONCLUSIONS
A series of PEHT-PPDO copolyesters with different composi-
tons have been successfully synthesized by chain-extension
reaction, using TDI as the chain extender, which were con-
firmed by FTIR and the molecular weights determined from
1H NMR or GPC. When the weight ratio of PEHT-OH to
PPDO-OH was suitable, the copolyester with the maximal
molecular weight could be obtained. The TG results indicated
that the thermal stability of PEHT-PPDO was improved com-
pared with PPDO homopolymer. The crystallization rate was
lowed due to their chain irregularity. The crystallization
behaviors of PEHT-PPDO were predominantly contributed by
PPDO segments. All the copolyester showed the good elonga-
tion at break and tensile strength which had great relation-
ships with their PEHT content. A study on the biodegradabil-
ity of the copolyesters is underway.
The authors gratefully acknowledge the National Key Technol-
ogy R and D Program (Contract Nos. 2007BAE28B06 and
2007BAE42B05), and the NMR analysis provided by the Ana-
lytical and Testing Center of Sichuan University.
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