Polytriazole/clay nanocomposites synthesized using in situ polymerization and click chemistry

Article abstract of DOI:10.1016/j.polymer.2009.11.015

This manuscript describes the preparation of polytriazole/clay nanocomposites through in situ polymerization of PTA, using click chemistry, in the presence of a propargyl-modified clay. The clay layers became exfoliated and dispersed well in the PTA matrix, thereby improving the thermal and mechanical properties of the clay. This approach can be extended to combine propargyl-modified clays with other azide- and alkyne-containing polymers.

Full text of DOI:10.1016/j.polymer.2009.11.015

Polymer 51 (2010) 430–436
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Polytriazole/clay nanocomposites synthesized using in situ polymerization and
click chemistry
*
Yun-Sheng Ye, Ying-Chieh Yen, Chih-Chia Cheng, Yu-Jyuan Syu, Yao-Jeng Huang, Feng-Chih Chang
Institute of Applied Chemistry, National Chiao-Tung University, Hsin-Chu, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
This manuscript describes the preparation of polytriazole/clay nanocomposites through in situ poly-
merization of PTA, using click chemistry, in the presence of a propargyl-modified clay. The clay layers
became exfoliated and dispersed well in the PTA matrix, thereby improving the thermal and mechanical
properties of the clay. This approach can be extended to combine propargyl-modified clays with other
azide- and alkyne-containing polymers.
Received 25 August 2009
Received in revised form
5 November 2009
Accepted 9 November 2009
Available online 27 November 2009
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Clay
In situ polymerization
Click chemistry
1. Introduction
achieve effective clay dispersion in the polymer matrix. In general,
exfoliated structures are more effective at improving properties of
One of the most effective click reactions at present is the Huisgen
1,3-dipolar cycloaddition reaction of azides and terminal alkynes
catalyzed by copper(I) complexes. This regioselective transformation
proceeds with short reaction times, a wide range of tolerated func-
tionality, high yields, and tolerance of humidity and oxygen [1–3]. As
a result, this reaction has been applied extensively to various fields of
materials science and polymer chemistry, such as branched den-
drimers [5,6], surface modification [4,7–9], macromolecular engi-
neering [10–14], nanostructured semiconductors [15] and polymer/
clay nanocomposites [16,17]. The elaboration of linear polytriazoles
(PTAs) through catalyzed and non-catalyzed click step growth
polymerizations of dialkyne and diazide monomers, oligomers, and
polymers has been investigated thoroughly [18–21]. Because PTAs
are 1,2,3-triazole resins, they are thermally and thermo-oxidatively
stable polymersdimportant characteristics for their application as
macromolecules [22,23].
the polymer (e.g., flame resistance and barrier, mechanical, elec-
tronic, and optical properties) than are intercalated structures
because exfoliated nanostructures exhibit stronger synergistic
effects of the polymer matrix and silicate layers. In situ polymeri-
zation appears to be a promising method for the preparation of
exfoliated nanocomposites [16,28–36].
In this paper, we report that PTA/clay nanocomposites (e.g., PTA 1,
Scheme 1) possess dramatically improved thermal (Tg ¼ 123.5 ꢀC;
Td10 ¼ 348.7 ꢀC; CTE ¼ 215.5
m
m/m ꢀC) and mechanical properties
(max. stress ¼ 34.9 MPa) relative to those of the neat PTA
(Tg ¼ 104.5 ꢀC; Td10 ¼ 337.6 ꢀC; CTE ¼ 337.9
m
m/m ꢀC; max.
stress ¼ 24.2 MPa). We prepared a propargyl-functionalized clay and
reacted it with azides and alkynes to form PTA polymers through
click reactions. In principle, this approach can be extended to the
reactions of other propargyl-modified clays with other azide- and
alkyne-containing polymers.
Polymer/clay nanocomposites have attracted great interest
because of their engineering properties are often superior to those of
the corresponding neat polymers [24–26]. Several approaches have
been developed for the preparation of polymer-layered silicate
nanocomposites, including solution exfoliation, melt intercalation,
and in situ polymerization [27]. The most important challenge,
however, when fabricating polymer/clay nanocomposites is how to
2. Experimental section
2.1. Materials
Ethanol (ꢁ99.5%, Aldrich), HCl (37%, Sigma–Aldrich), acetic
anhydride (ꢁ99%, Sigma–Aldrich), sodium hydroxide (ꢁ97.0%,
Sigma–Aldrich), sodium azide (ꢁ99.0%, Sigma–Aldrich), tetrabutyl-
ammonium bromide (99%, Aldrich), bromoundecanoic acid (99%,
Aldrich), anhydrous magnesium sulfate (99%, Sigma–Aldrich),
* Corresponding author. Tel.: þ886 3 5727077; fax: þ886 3 5719507.
E-mail address: changfc@mail.nctu.edu.tw (F.-C. Chang).
0032-3861/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2009.11.015

Y.-S. Ye et al. / Polymer 51 (2010) 430–436
431
+
NH3
+H3N
O
+
O
O
Clay
+
NH3
PBA
propargyl-functionalized clay
(b) In Situ Polymerization
(a) Model ''Click''Reaction
O
N3
N3
(C10H20)
O
O
+
+
N3
OH
ADA
BAB
PBPB
+H3N
HOOC-(C10H20
)
N
N
N
O
+H3N
O
N
N
N
(C10H20)-COOH
O
+
NH3
C10-Acid-functionalized clay
n
N
N
O
O
N
N
N
N
PTA-clay nano composites
Scheme 1. Propargyl-functionalized clay and its click reactions with ADA (a, mode click reaction) and PBPB and BAB (b, in situ polymerization).
p-aminophenol (99%, Acros Organics), copper(I) iodide (ꢁ97%, Rie-
del–de Hae¨n), and sodium montmorillonite (Naþ-MMT; cationic
exchange capacity: 1.45 meq/g; Nanocor Co) were used as received.
p-Xylylene dichloride (ꢁ98.0%, Sigma–Aldrich) was recrystallized
from MeOH prior to use. Propargyl bromide (ca. 80 vol% in toluene,
Fluka) was distilled prior to use.
9.80 (e) ppm (Figure S3); 13C NMR (DMSO-d6):
(3), 78.80 (1), 80.16 (2), 115.33 (5), 121.42 (6), 133.58 (7), 153.89 (4),
168.76 (8) ppm (Figure S4).
d
¼ 24.38 (9), 56.15
2.2.3. 4-(Prop-2-ynyloxy)benzenaminium (PBA)
HCl (36%, 70 mL) was added to a solution in N-[4-(prop-2-ynyl-
oxy)phenyl]acetamide (8.5 g, 45 mmol) in EtOH (70 mL) and then
the mixture was stirred at 60 ꢀC for 3 h. After cooling to ambient
temperature, the product was filtered off and washed with EtOAc to
give PBA as a brown solid (69%). M.p. ¼ 50 ꢀC; 1H NMR (DMSO-d6):
2.2. Preparation of monomers
2.2.1. N-(4-Hydroxphenyl)acetamide
Acetic anhydride (12.3 g, 120 mmol) was added to a stirred
solution of p-aminophenol (10.9 g, 100 mmol) in water (40 mL) and
then the suspension was stirred at 60 ꢀC until a clear solution was
obtained. After cooling to ambient temperature, the precipitate was
filtered off, washed with deionized water, and then recrystallized
d
¼ 3.57 (a), 4.78 (b), 7.05 (c), 7.32 (d), 10.37 (e) ppm (Figure S5); 13
C
NMR (DMSO-d6):
125.04 (7), 157.01 (6) ppm (Figure S6).
d
¼ 56.40 (3), 79.0 (1,2), 116.44 (5,6), 80.16 (2),
2.2.4. 4,40-(Propane-2,2-diyl)bis[(prop-2-ynyloxy)benzene] (PBPB)
from water (79%). M.p. ¼ 168 ꢀC; 1H NMR (CDCl3):
d
¼ 2.00 (e), 6.73
PBPB was synthesized (89%) using a procedure similar to that
described above [N-(4-Hydroxphenyl)acetamide replaced by
bisphenol A]; its purification was performed using the same proce-
dure used for N-[4-(prop-2-ynyloxy)phenyl]acetamide. M.p. ¼ 78 ꢀC;
(b), 7.39 (c), 9.18 (a), 9.64 (d) ppm (Figure S1); 13C NMR (CDCl3):
d
¼ 24.53 (6), 115.86 (2), 122.0 (3), 131.78 (4), 153.80 (1), 168.51 (5)
ppm (Figure S2).
1H NMR (CDCl3):
d
¼ 1.68 (e), 2.53 (a), 4.68 (b), 6.89 (c), 7.17 (d) ppm
2.2.2. N-[4-(Prop-2-ynyloxy)phenyl]acetamide
(Figure S7); 13C NMR (CDCl3):
d
¼ 31.54 (9), 42.26 (8), 55.99 (3), 75.68
N-(4-Hydroxyphenyl)acetamide (9.7 g, 60 mmol), NaOH (3.2 g,
80 mmol), deionized water 100 mL and tetrabutylammonium
bromide (1.9 g, 6.0 mmol) were added into a three-necked round-
bottom flask equipped with a magnetic stirrer, a reflux condenser,
and a N2 gas inlet tube and then the system was heated to 70 ꢀC.
Propargyl bromide (9.5 g, 80 mmol) was added dropwise over 3 h
and then the mixture was maintained at 70 ꢀC for 10 h. The reaction
product was washed several times with deionized water to remove
tetrabutylammonium bromide and the salts formed in the reaction.
The product was recrystallized from EtOH (87%). M.p. ¼ 122 ꢀC; 1H
(1), 79.25 (2), 114.47 (5), 128.20 (6), 144.37 (7), 155.61 (4) ppm
(Figure S8).
2.2.5. 1,4-Bis(azidomethyl)benzene (BAB)
p-Xylylene dichloride (8.8 g, 50 mmol), NaN3 (9.75 g, 150 mmol),
DMF (100 mL), and benzene (100 mL) were added into a three-
necked round-bottom flask equipped with a magnetic stirrer and
a reflux condenser. The reaction mixture was slowly heated to 80 ꢀC
and then maintained at that temperature for 12 h. It was then poured
into a beaker containing deionized water (200 mL). The organic layer
was separated and then the aqueous layer was extracted three times
NMR (DMSO-d6):
d
¼ 2.00 (f), 3.51 (a), 4.74 (b), 6.89 (c), 7.49 (d),

432
Y.-S. Ye et al. / Polymer 51 (2010) 430–436
with benzene. All combined organic phases were dried overnight
(MgSO4) and then the benzene was distilled off to yield a light-yellow
temperature (Tg) was determined by using a TA2000 differential
scanning calorimeter (DSC) operated from 0 to 120 ꢀC at a heating
rate of 10 ꢀC/min. Molecular weights and molecular weight distri-
butions were determined through gel permeation chromatography
(GPC) using a Waters 510 HPLC equipped with a 410 Differential
Refractometer, a refractive index (UV) detector, and three Ultra-
styragel columns (100, 500, and 103 Aꢀ) connected in series in order
of increasing pore size. The polymer solution was purified by filtra-
solid (81%). M.p. ¼ 27–29 ꢀC; 1H NMR (CDCl3):
d
¼ 4.32 (b), 7.35 (a)
ppm (Figure S9); 13C NMR (CDCl3):
ppm (Figure S10).
d
¼ 54.59 (1),128.98 (3),135.97 (2)
2.2.6. 11-Azidoundecanoic acid (ADA)
NaN3 (6.5 g, 100 mmol) was added to a solution of 11-bro-
moundecanoic acid (7.95 g, 30 mmol) in DMSO and then the clear
colorless solution was stirred at room temperature overnight. The
reaction mixture was diluted with water and then HCl was added
cautiously. After cooling the reaction mixture, the aqueous phase
was then extracted three times with EtOAc. The combined organic
layers were washed three times with water and then with brine
before drying (MgSO4). After filtration, all volatiles were evaporated
under reduced pressure to yield the crude product as pale yellow
oil. Purification through flash column chromatography (hexane)
tion through a 0.2-mm syringe filter before the GPC measurement.
The coefficients of thermal expansion (CTEs) were obtained using
a TA 2940 thermomechanical analyzer (TMA); the applied force
applied was 0.005 N and the sample was heated from 25 to 120 ꢀC at
a rate of 5 ꢀC/min. The morphology of the clay in the hybrids was
observed using a JEOL JEM-1200CX-II transmission electron micro-
scope operated at 120 kV. Wide-angle X-ray diffraction (WAXD)
spectra were recorded for powdered samples using a Rigaku D/max-
2500 type X-ray diffraction instrument. The tensile properties were
measured according to ASTM 638 on a Shimadzu AG-50kNE
universal tester. The crosshead speed was set at 1 mm/min.
gave the product as a waxy solid (75%). 1H NMR (CDCl3):
e), 1.58 (c), 2.31 (b), 3.20 (f), 10.29 (a) ppm (Figure S11); 13C NMR
(CDCl3):
d
¼ 1.26 (d,
d
¼ 26.86 (3), 27.01 (7), 29.20 (4,5), 34.24 (2), 51.59 (6),
180.59 (1) ppm (Figure S12).
3. Results and discussion
2.3. Modification of clay
3.1. Characterization of propargyl-functionalized modified clay
The propargyl-functionality modified clay was prepared through
cationic exchange between Naþ-MMT and the clay-modifying agent
(PBA) in an aqueous solution. Na-MMT was dispersed in deionized
water at 60 ꢀC, and a separate solution of PBA in deionized water was
heated and mixed at 60 ꢀC for 24 h. The propargyl-functionality
modified clay was recovered by filtration, followed by repeated
washings of the filter cake with deionized water to remove the
excess of ions. The final product was dried in a vacuum oven at room
temperature for 24 h.
Scheme 1 summarizes the various stages during the in situ
intercalative polymerization of PTA using MMT nanoclays. In the
first stage, the silica layers of the clay were modified with prop-
argyl-functionality through ion exchange. In the XRD pattern in
Fig. 1(b), the pristine MMT exhibits a basal spacing of 1.27 nm at
a value of 2q
of 6.98ꢀ. This signal shifted slightly to 6.28ꢀ after the
pristine clay had been modified with PBA, suggesting interlayer
expansion. In the FTIR spectrum of pristine MMT [Fig. 1(a)], the
band at 3628 cmꢂ1 is typical of smectities, resulting from the
internal OH groups of the clay minerals. We assign the signal at
1647 cmꢂ1 to the water deformation band. After modification with
propargyl-functionality, a characteristic propargyl signal appears
near 3288 cmꢂ1. Moreover, the XRD pattern in Fig. 1(b) reveals that
2.4. Model click reaction
The propargyl-modified clay (0.25 g), ADA (0.8 mL, 3.9 mmol),
and DMF (10 mL) were placed in a round-bottom flask and stirred. A
solution of CuI (5 mol%) in water (0.5 mL) was added to the mixture,
which was heated overnight in an oil bath at 70 ꢀC. The particles
were recovered using the procedure described above.
the peak at a value of 2q
of 6.98ꢀ shifted to 6.51ꢀ after modification.
These FTIR spectra and XRD patterns provide evidence for the
successful preparation of the propargyl-functionalized clay.
To confirm that clay layers could undergo click chemistry, we
performed a model reaction between the propargyl-functionalized
clay and the azide groups of ADA. The characteristic propargyl
signal at 3288 cmꢂ1 disappeared and a new signal appeared near
1740 cmꢂ1, corresponding to the carbonyl group of ADA [Fig. 1(a)].
Moreover, the XRD pattern in Fig. 1(b) reveals that the peak at an
initial value of 2q
of 6.51ꢀ shifted to 5.58ꢀ after the click reaction.
These results indicate that the azide-functionalized ADA had
become attached to the clay layerdin particular, onto the surface of
the interlayer of the silicatedthrough click chemistry.
2.5. Preparation of PTA/clay nanocomposites
The propargyl-functionalized modified clay (1, 3, or 5 wt% of the
monomer) was mixed with the monomers PBPB and BAB and DMF
in a three-necked flask and heated at 70 ꢀC for 30 min. CuI
(5.0 mol%) was added and the mixture was stirred for 4 h. The PTA-
clay nanocomposites were obtained through precipitation; they
were then dried at 50 ꢀC under vacuum for 24 h 1H NMR (DMSO-
d6):
d
¼ 1.53 (e), 5.03 (c), 5.51 (b), 6.85 (c), 7.08 (h), 7.33 (d,g), 8.23
(a) ppm (Figure S13); 13C NMR (DMSO-d6):
d
¼ 31.25 (1), 36.61 (11),
3.2. Synthesis and characterization of PTA/clay nanocomposites
41.74 (12), 53.12 (6), 61.67 (7), 114.62 (8), 125.46 (4), 128.25 (3,30),
128.88 (9), 136.84 (5), 143.70 (10), 156.78 (7) ppm (Figure S14).
We mixed the propargyl-functionalized modified clay with the
BAB and PBPB monomers to undergo polymerization to produce
a series of PTA-clay composites (Scheme 1). Table 1 shows the
intrinsic viscosity, molecular weights (Mw) and polydispersity
indices (PDIs) of the PTA and its composites. The addition of clay
resulted in a slight increase in the intrinsic viscosity and Mw. It is
attributed to that MMT might either act as a catalytic agent or
inactivates polymerization; resulting in a higher molecular weight
of the PTA with proceeding polymerization [37]. This is also resulted
in a slight decrease of PDI as clay loading was increased [38,39]. The
efficiency of the click polymerizationwas clearlyevident through 1H
NMR spectroscopic analysis (Fig. 2). The formation of triazole units
2.6. Characterization
FTIR spectra were recorded on a Nicolet Avatar 320 FTIR spec-
trophotometer over the range 4000–400 cmꢂ1 at a resolution of
1.0 cmꢂ1 under a continuous flow of N2. 1H NMR spectra were
recorded at 25 ꢀC on an INOVA 500 MHz NMR spectrometer. A
DuPont Q100 thermogravimetric analyzer (TGA) was used to
investigate the thermal stability of the nanocomposites; the samples
(ca. 10 mg) were heated from ambient temperature to 850 ꢀC under
a N2 atmosphere at a heating rate of 20 ꢀC/min. The glass transition

Y.-S. Ye et al. / Polymer 51 (2010) 430–436
433
h
n
a
g
e
c
d
a
N
N
N
N
O
b
O
f
(1) Clay
N
H2O
N
d,g
h
e
f
b
(2) propargyl-functionalized clay
c
a
d6
PTA
3288 cm-1
Propargyl groups
(3) C10-acid-functionalized clay
PTA 5
1740 cm-1
C=O
10
8
6
4
2
4000
3500
3000
2500
2000
1500
Wavelength (cm-1)
Chemical shift (ppm)
Fig. 2. 1H NMR spectra of PTA and PTA 5.
b
6.98 o
For the PTA 1 nanocomposite, the d001 signal of the pristine MMT
had disappeared completely, indicating the formation of an exfo-
liated structure in the nanocomposite. Moreover, upon incorpo-
rating 1 wt% of clay, the amorphous peak of the neat PTA
(1) Clay
(2
q
¼ 20.23ꢀ) shifted to a slightly lower value and a new amorphous
peak appeared at a value of 2q
of 30.81ꢀ. A high distribution of clay
plates in the PTA matrix tends to expand the intermolecular main
chain spacing and reduce the intramolecular distance between the
rigid polymer backbones [40–43]. PTAs 3 and 5 exhibited small and
broad peaks having d-spacings of 1.48 and 1.67 nm, indicating that
both exfoliated and intercalated structures were present. The
intensity of the intercalated peak increased upon increasing the
concentration of the clay, suggesting a higher fraction of interca-
lated clay [44].
(2) propargyl-functionalized clay
(3) C10-acid-functionalized clay
5
10
15
20
25
30
35
40
To further investigate the dispersion of the clay in the polymer
matrix, we recorded TEM micrographs, In Fig. 4, the dark lines
represent clay layers; the bright areas, the PTA matrix. The XRD
spectrum of PTA 1 exhibited only the broad peak of PTA matrix; its
TEM micrographs [Fig. 4(a) and (d)] reveal that most of the clay layers
lost their stacking structure and disorderly dispersed in the PTA
2-Theta (degree)
Fig. 1. (a) FTIR spectra of (1) the clay, (2) the propargyl-functionalized clay, and (3) the
C10-acid-functionalized clay. (b) X-ray diffraction curves of (1) the clay, (2) the prop-
argyl-functionalized clay, and the (3) C10-acid-functionalized clay.
was evidenced through the appearance of a signal at 8.21 ppm and
shifts of the signals of the methylene protons adjacent to the alkyne
(4.71 ppm) and azide (4.33 ppm) units to 5.57 and 5.06 ppm,
respectively. Moreover, the broad signals in the spectrum of the
polymer reveal that a high molar mass PTA/clay composite had
formed.
d=1.29 nm
(a) MMT
(b) Neat PTA
(c) PTA 1
(d) PTA 3
(e) PTA 5
d=0.44 nm
3.3. Morphology of the PTA/clay nanocomposites
(a)
Fig. 3 displays XRD patterns of the pristine MMT, neat PTA, and
a series of PTA-clay composites incorporating various clay contents.
(b)
(c)
Table 1
(d)
(e)
Polymerization of PTA in the presence of various amounts of clay.
Sample
Theoretical clay
loading (wt%)a
Intrinsic viscosity
Mw (ꢃ106)
Mw/Mn
b
(dL gꢂ1
)
PTA
0
1
3
5
0.63
0.69
0.73
0.71
5.54
5.89
5.95
6.12
2.98
2.75
2.49
2.58
PTA 1
PTA 3
PTA 5
10
20
30
40
2-Theta (degree)
a
Determined from the initial clay loading and the mass of the monomer used.
Determined at 25 ꢀC.
Fig. 3. Wide-angle X-ray diffraction patterns of the neat PTA and PTA-clay nano-
composites incorporating various clay contents.
b

434
Y.-S. Ye et al. / Polymer 51 (2010) 430–436
Fig. 4. TEM images of the (a) PTA 1 (80k), (b) PTA 3 (80k), (c) PTA 5 (80k), and (d) PTA 1 (10k) nanocomposites.
matrix. As the clay loading increased, certain degrees of aggregation
led to the formation of intercalated stacks, as observed in Fig. 4(b) and
(c). The TEM images in Fig. 4(a) and (b) clearly reveal that the exfo-
liated and intercalated structures coexisted in the PTA matrix.
3.4. Thermal and mechanical properties of PTA-clay
nanocomposites
Fig. 5 and Table 2 summarize the glass transition temperatures
(Tg) of the PTA-clay nanocomposites obtained from DSC measure-
ments. All of the PTA-clay nanocomposites exhibited higher values of
Tg than that of the neat PTA, due to restriction of the PTA chain
motion. The fully exfoliated PTA 1 possessed a higher value of Tg
relative to those of the partially exfoliated or intercalated composites
(PTAs 3 and 5). An excessive level of clay plates above the saturation
content tended to result in aggregation, thereby reducing the
content of exfoliated clay in the PTA matrix. As a result, the ability to
restrict chain motion was reduced, resulting in lower values of Tg
(PTA 1 > PTA 3 > PTA 5).
(a)
104.6 °C
(b)
(c)
123.5 °C
Fig. 6 displays TGA thermograms of the PTA/clay nanocomposites;
Table 2 summarizes the data. The values of Td10 of the PTA/clay
(d)
112.8 °C
Table 2
111.5 °C
(a)
Neat PTA
PTA 1
Thermal and mechanical properties of PTA-clay nanocomposites.
(b)
(c)
(d)
Sample Tg
Td10
(ꢀC)a (ꢀC)
Td60
(ꢀC)
CTE
(m
Tensile
Tensile
Elongation
PTA 3
m/mꢀC) strength modulus at break (%)
PTA 5
30–100 ꢀC (MPa)
(GPa)
PTA
104.5 337.6 386.1 337.9
123.5 342.9 431.9 215.5
112.8 345.7 431.8 208.9
111.5 348.7 431.9 191.0
24.2
36.9
32.0
29.9
3.95
3.79
4.63
4.50
6.01
8.81
6.51
6.60
25
50
75
100
125
150
175
PTA 1
PTA 3
PTA 5
Temperature (°C)
Fig. 5. DSC thermograms of the neat PTA and PTA-clay nanocomposites incorporating
various clay contents.
a
Determined using DSC.

Y.-S. Ye et al. / Polymer 51 (2010) 430–436
435
clay in the PTA matrix and, thereby, decrease its ability to enhance
the mechanical properties.
100
90
100
80
348.7 °C
Td10
4. Conclusions
80
337.6 °C
70
We have prepared PTA/clay nanocomposites through in situ
polymerization of PTA using click chemistry in the presence of
a propargyl-functionalized modified clay, as a new route toward
high-performance PTA materials. The clay layers of PTA 1 were fully
exfoliated and well dispersed in the PTA matrix, resulting in the
greatest improvement in its thermal and mechanical properties. A
clay content greater than the optimized saturation content caused
these clay plates to aggregate (in the form of intercalation) and
reduce the degree of exfoliation to below its saturation level within
the PTA matrix; as a result, both the thermal and mechanical
properties deteriorated.
60
300
320
340
360
380
400
431.9 °C
60
Td60
386.1 °C
Neat PTA
PTA 1
PTA 3
PTA 5
40
100
200
300
400
500
600
700
800
Temperature (°C)
Fig. 6. TGA thermal degradation patterns of the neat PTA and PTA-clay nano-
composites incorporating various clay contents.
Appendix. Supplementary data
Supplementary data associated with this article can be found in
the online version, at doi:10.1016/j.polymer.2009.11.015.
nanocomposites improved only slightly, whereas the value of Td60
showed a large increase, by 46 ꢀC, relative to that of the neat PTA. We
attribute the improvement in thermal stability of the PTA polymer
filled with the nanoclay to the formation of a clay char that acted as
a mass transport barrier and an isolator between the bulk polymer
and the surface, where combustion occurred [44–47]. In addition, the
restricted thermal motion of the polymer chains localized within the
clay galleries also promoted the thermal stability of the polymer.
Table 2 reveals that the CTEs of the PTA/clay nanocomposites
decreased upon increasing the clay content. We attribute the lower
CTEs for the composites to the silicate rigidity and fine dispersion of
the clay platelets in the PTA matrix. The incorporation of the
modified clay reduced the CTEs and provided products exhibiting
improved dimensional stability.
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