Semiaromatic polyamides containing ether and different numbers of methylene (2-10) units: Synthesis and properties

Article abstract of DOI:10.1039/c4ra10074c

A series of semiaromatic difluorobenzamide monomers was synthesized by the reaction of diamine and 4-fluorobenzoic chloride using a facile interfacial method. These syntheses were conducted to react the monomers with 1,1-bis(4-hydroxyphenyl)-1-phenylethan

Full text of DOI:10.1039/c4ra10074c

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Semiaromatic polyamides containing ether and
different numbers of methylene (2–10) units:
synthesis and properties†
Cite this: RSC Adv., 2014, 4, 63006
a
Gang Zhang, Yu-xuan Zhou,b Yu Kong,c Zhi-min Li,c Sheng-Ru Longa
*
ad
*
and Jie Yang
A series of semiaromatic difluorobenzamide monomers was synthesized by the reaction of diamine and 4-
fluorobenzoic chloride using a facile interfacial method. These syntheses were conducted to react the
monomers with 1,1-bis(4-hydroxyphenyl)-1-phenylethane (BHPPE), so as to prepare semiaromatic
polyamides containing ether units by the method of nucleophilic polycondensation. These had excellent
thermal properties with glass transition temperatures (Tg) of 134.4–195.6 ꢀC and initial degradation
temperatures (Td) of 405–443 ꢀC. The activation energies of degradation were in the range of
180.1–275.9 kJ molꢁ1. The resultant polymers can be dissolved in strong polar solvents and supply a
tough film with a tensile strength of 89–105 MPa. Also, we found that the complex viscosities of these
semiaromatic polyamides ranged from 77 to 688 Pa s at 290 ꢀC. They had the appropriate complex
viscosities for melt processing. Moreover, they had much wider processing windows than those of
traditional semiaromatic polyamides such as poly(hexamethylene terephthalamide) (PA6T). Interestingly,
some of the resultant polymers were found to be naturally self-retardant.
Received 9th September 2014
Accepted 6th November 2014
DOI: 10.1039/c4ra10074c
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outstanding properties, they also have limited applications
because they can only be processed by special methods (they do
not melt below their decomposition temperatures).12,13 The high
Introduction
Nylons (such as PA6 or PA66) are a type of engineering ther-
moplastic that have been widely applied in modern industrial
and commercial applications in the last three decades. They can
be easily processed by melt processing to form different kinds of
structural parts, polymer lms and polymer bers.1–3 With
increasingly stringent requirements, applications of aliphatic
polyamides are limited in some elds because of their poor
dimensional stability and thermal properties, especially in
surface mount technology (SMT) and the shells of automobile
engines. To improve the thermal properties of polyamides, the
fabrication method for polyamide compounds,4 or the incor-
poration of aromatic rings, are efficient approaches.5–9 Aromatic
polyamides such as poly(p-phenylene terephthalamide)
(PPTA)10 and poly(m-phenyleneisophthalamide) (PMIA)11 have
been commercially accepted in industry for their excellent
balance of mechanical and thermal properties. Despite their
melting temperatures of aromatic polyamides are attributed to
the high density of aromatic rings and strong inter-chain forces,
mainly hydrogen bonding, that enhance an effective molecular
packing.14 Also, semiaromatic polyamides have been developed
rapidly in the last 20 years. The semiaromatic polyamides have
been noted for their high thermal stability and chemical resis-
tance. However, only a few semiaromatic polyamides are
commercially available. These include copolymers of PA6T,15
poly(nonamethylene terephthalamide) (PA9T)16–19 and the
products of Dupont, Evonik, Mitsui, and Solvay and so on.
Usually, if the melting point of a semiaromatic polyamide is
higher than 340 ꢀC, it is thought to be not suitable for thermal
processing.20 Thus, melt processing is impractical for those
semiaromatic polyamides with short aliphatic diamines (2–7
CH2's) because their melt temperatures surpass the thermal
decomposition temperatures, such as PA4T (Tm ¼ 430 ꢀC, Td ¼
350 ꢀC) and PA6T (Tm ¼ 370 ꢀC, Td ¼ 350 ꢀC). Therefore, several
synthetic approaches have been developed, suchꢀas incorpo-
aInstitute of Materials Science & Technology, Analytical & Testing Center, Sichuan
University, Chengdu 610064, P. R. China. E-mail: gangzhang@scu.edu.cn; ppsf@
scu.edu.cn; Fax: +86-28-8541-2866
bCollege of Chemistry, Sichuan University, Chengdu, 610064, P. R. China
cCollege of Polymer Materials Science and Engineering of Sichuan University, Chengdu,
610065, P. R. China
rating naphthalene rings (Tm ¼ 320 C, Td ¼ 495 C),21 benzy-
ꢀ
lidene structure (Tm ¼ 290 C),22 bulky pendant groups (Tg z
ꢀ
270 ꢀC, Td z 500 ꢀC),14 noncoplanar biphenylene moieties
(Tg z 300 ꢀC, Td-10% z 510 ꢀC),23 azo groups,24,25 sulfone units,26
triazole units,27 thioether units28 and long-chain diamines
(Tm z 290 ꢀC, Td z 490 ꢀC)29 [such as PA9T (Tm ¼ 305 ꢀC,
Td-5% ¼ 464 ꢀC), PA-10T (Tm ¼ 315 ꢀC, Td-5% ¼ 472 ꢀC),30 PA-12T
dState Key Laboratory of Polymer Materials Engineering (Sichuan University),
Chengdu, 610065, P. R. China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c4ra10074c
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(Tm ¼ 295 ꢀC, Td ¼ 429 ꢀC),31 PA-18T (Tm ¼ 245 ꢀC), and so on] (N–H), 1633 (–CO–), 3053 (C–H aromatic ring), 2944, 2883
into the polymer backbones. It is known that the ether linkage is (–CH2–), 1604, 1559, 1506 (C]C aromatic ring), 854 (para
a exible bond. It can be incorporated into the polymer back- substituent of the aromatic ring). NMR [400 MHz, deuterated
bone to improve the resin's processability, as in the cases of dimethyl sulfoxide (DMSO-d6)/tetramethylsilane (TMS), ppm]:
poly(arylene ether amide)2 and poly(arylene ether sulfone).32 3.422–3.473 (m, 4H, H1), 7.266–7.325 (m, 4H, H2), 7.888–7.931
They all have excellent processability, mechanical, thermal and (m, 4H, H3), 8.627 (s, 2H, H4); 39.67 (C1), 115.23 (C2), 129.83
antioxidant properties. Therefore, in the work described here, (C3), 130.98 (C4), 162.54 (C5) and 165.41 (C6). The other
we expected to incorporate the ether (–O–) and different monomers were prepared using a similar method to that used
numbers of methylene units into the main chain of semi- for BFBE.
aromatic polyamides to improve their properties. In this study,
1,4-N,N0-bis(4-uorobenzamide) butane (BFBB)
ve kinds of semiaromatic diuorobenzamide monomers
which contained 2–10 CH2 groups were prepared by the reaction
of 4-FBC with different diamine (ethylenediamine, 1,6-hex-
anediamine, 1,4-butanediamine, 1,8-octanediamine, and 1,10-
decanediamine). Then these were reacted with BHPPE by
nucleophilic polycondensation to prepare semiaromatic poly-
amides (usually, the polyamides were prepared by the reaction
of dicarboxylic acid (dicarboxylic chloride) and diamine with
electrophilic substitution). The effects of chemical structure on
the thermal performances, mechanical properties, process-
ability, ame retardant properties and thermal degradation
kinetics of the resultant semiaromatic polyamides were inves-
tigated in detail.
Yield: 283.2 g, 85.3%. Elemental analysis (%): found: C, 65.33
(65.05); H, 5.41 (5.46); N, 8.48 (8.43) (data in brackets are
calculated). Melt point: 228.4–231.8 ꢀC. FT-IR (KBr, cmꢁ1): 3314
(N–H), 1630 (–CO–), 3036 (C–H aromatic ring), 2948, 2876
(–CH2–), 1605, 1540, 1504 (C]C aromatic ring), 850 (para
substituent of the aromatic ring). NMR [400 MHz, deuterated
dimethyl sulfoxide (DMSO-d6)/tetramethylsilane (TMS), ppm]:
1.558 (s, 4H, H1), 3.272–3.330 (d, 4H, H2), 7.261–7.306 (m, 4H,
H3), 7.886–7.922 (m, 4H, H4), 8.492 (s, 2H, H5); 26.65 (C1), 39.66
(C2), 115.17 (C3), 129.74 (C4), 131.07 (C5), 162.49 (C6) and
165.02 (C7).
1,6-N,N0-bis(4-uorobenzamide) hexane (BFBH)
Experimental
Materials
Yield: 320.0 g, 88.9%. Elemental analysis (%): found: C, 66.39
(66.65); H, 6.17 (6.15); N, 7.89 (7.77) (data in brackets are
calculated). Melt point: 197.8–200 C. FT-IR (KBr, cmꢁ1): 3317
ꢀ
BHPPE was prepared according to the method reported earlier
by our group,33 and 4-uorobenzoic chloride (4-FBC) (99.5%,
Lanning Chemical Company Limited), sodium hydroxide
(NaOH) (AR, SiChuan ChengDu ChangLian Chemical Reagent
Company), N-methyl-2-pyrrolidone (NMP) (JiangSu NanJing
JinLong Chemical Industry Company), ethylenediamine, 1,4-
butanediamine, 1,6-hexanediamine, 1,8-octanediamine, 1,10-
decanediamine and other reagents were obtained
commercially.
(N–H), 1630 (–CO–), 3033 (C–H aromatic ring), 2937, 2868
(–CH2–), 1606, 1541, 1504 (C]C aromatic ring), 850 (para
substituent of the aromatic ring). 1H-NMR [400 MHz, deuter-
ated dimethyl sulfoxide (DMSO-d6)/tetramethylsilane (TMS),
ppm]: 1.333 (s, 4H, H1), 1.504–1.536 (t, 4H, H2), 3.217–3.266 (d,
4H, H3), 7.258–7.302 (m, 4H, H4), 7.880–7.915 (m, 4H, H5),
8.463 (s, 2H, H6); 26.20 (C1), 29.05 (C2), 39.67 (C3), 115.17 (C4),
129.73 (C5), 131.11 (C6), 162.47 (C7) and 164.97 (C8).
1,8-N,N0-bis(4-uorobenzamide) octane (BFBO)
1,2-N,N0-bis(4-uorobenzamide) ethane (BFBE) (Scheme 1)
Yield: 327.1 g, 84.3%. Elemental analysis (%): found: C, 68.35
(68.02); H, 6.73 (6.75); N, 7.34 (7.21) (data in brackets are
BFBE was prepared according to the following procedure: 4-FBC
(320 g, 2.02 mol) and dichloromethane (2000 ml) were added
into a 5000 ml three-necked ask equipped with mechanical
stirrer and thermometer. Then the mixture of ethylenediamine
(60 g, 1 mol) and NaOH (80 g, 2 mol) (dissolved in 1000 ml
deionized water) and sodium dodecyl sulfate (3 g, 0.01 mol) was
added into the ask dropwise within 2 h. The mixture was
calculated). Melt point: 174–176.8 C. FT-IR (KBr, cmꢁ1): 3318
ꢀ
(N–H), 1631 (–CO–), 3064 (C–H aromatic ring), 2935, 2855
(–CH2–), 1606, 1541, 1505 (C]C aromatic ring), 849 (para
substituent of the aromatic ring). 1H-NMR [400 MHz, deuter-
ated dimethyl sulfoxide (DMSO-d6)/tetramethylsilane (TMS),
ppm]: 1.97 (s, 8H, H1–H2), 1.510 (s, 4H, H3), 3.212–3.260 (m,
4H, H4), 7.259–7.303 (m, 4H, H5), 7.885–7.919 (m, 4H, H6),
8.457 (s, 2H, H7); 26.44 (C1), 28.72 (C2), 29.04 (C3), 39.68 (C4),
115.18 (C5), 129.72 (C6), 131.13 (C7), 162.46 (C8) and 164.93
(C9).
ꢀ
vigorously stirred at 5–10 C for about 6 h. Aer that the reac-
tion mixture was evaporated under 50 ꢀC to recover the solvent
dichloromethane. Then the crude product was washed with hot
deionized water, the mixture was ltered, and the above steps
were repeated three times. Next, the wet lter cake was recrys-
tallized from ethanol to afford needle-like crystals. The puried
product was then vacuum-dried at 80 ꢀC for more than 12 h to
yield colorless crystals of BFBE.
1,10-N,N0-bis(4-uorobenzamide) decane (BFBD)
Yield: 338.2 g, 81.3%. Elemental analysis (%): found: C, 69.39
Yield: 263.6 g, 86.7%. Elemental analysis (%): found: C, 62.93 (69.21); H, 7.24 (7.26); N, 6.96 (6.73) (data in brackets are
(63.15); H, 4.60 (4.64); N, 9.31 (9.21) (data in brackets are calculated). Melt point: 170–172.4 C. FT-IR (KBr, cmꢁ1): 3321
ꢀ
calculated). Melt point: 234–236.4 C. FT-IR (KBr, cmꢁ1): 3302 (N–H), 1631 (–CO–), 3068 (C–H aromatic ring), 2923, 2852
ꢀ
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(–CH2–), 1606, 1538, 1504 (C]C aromatic ring), 849 (para performed with a Waters 1515 performance liquid chromatog-
substituent of the aromatic ring). 1H-NMR [400 MHz, deuter- raphy pump, a Waters 2414 differential refractometer (Waters
ated dimethyl sulfoxide (DMSO-d6)/tetramethylsilane (TMS), Co., Milford, MA) and a combination of Styragel HT-3 and HT-4
ppm]: 1.269 (s, 12H, H1–H3), 1.483–1.516 (t, 4H, H4), 3.202– columns (Waters Co., Milford, MA), the effective molecular
3.252 (m, 4H, H5), 7.257–7.301 (m, 4H, H6), 7.878–7.913 (m, 4H, weight ranges of which were 500–30 000 and 5000–800 000,
H7), 8.448 (s, 2H, H8); 26.44 (C1), 28.73 (C2), 28.92 (C3), 29.92 respectively. N,N-Dimethyl formamide (DMF) was used as an
(C4), 39.68 (C5), 115.20 (C6), 129.73 (C7), 130.87 (C8), 162.18 eluent at a ow rate of 1.0 ml minꢁ1 at 35 ꢀC. Polystyrene
(C9) and 164.83 (C10).
standards were used for calibration.
The samples of monomers were measured with an
elemental analyzer (EURO EA-3000). The melting points of the
monomers were measured with a micro melting point appa-
ratus (XRC-1). FT-IR spectroscopic measurements were per-
formed on a Nexus670 FT-IR instrument. H nuclear magnetic
resonance (NMR) spectra were obtained on a Bruker-400 NMR
spectrometer in deuterated dimethyl sulfoxide. Differential
scanning calorimetry (DSC) was performed on a Netzsch DSC
200 PC thermal analysis instrument. The heating rate for DSC
Polymer synthesis (as shown in Scheme 1)
A typical polymerization was performed as shown in Scheme 1.
NMP (150 ml), toluene (20 ml), BHPPE (29.0 g, 0.1 mol),
potassium carbonate (27.6 g, 0.2 mol) and BFBE (30.4 g, 0.1 mol)
were added into a 500 ml three-necked ask equipped with
“Dean Stark” trap, mechanical stirrer and thermometer. The
ask was heated to 160 ꢀC and maintained for about 2 h; during
this period, 26.7 ml of liquid was removed. Then the reaction
ask was heated to 200 ꢀC and maintained for another 8 h. Aer
that, the reaction solution was poured into water, with stirring,
to precipitate white brous polymers. The collected
polymer was washed with water and ethanol, pulverized to a
powder, washed with water and ethanol again, and dried in a
vacuum oven at 100 ꢀC for 12 h to give BHPPE-2. (Yield: 51.4 g,
92.8%).
measurements was 10 C minꢁ1. Thermogravimetric analysis
ꢀ
(TGA) was performed on a TGA Q500 V6.4 Build 193 thermal
analysis instrument with a heating rate of 5–40 ꢀC min under a
nitrogen atmosphere. The polymer powder was processed into
the sheet shape by a hydraulic press (YJAC, Chengdu Hangfa
ꢀ
Group, China) at 290 C with a pressure of 8 MPa for 10 min.
Then the sheets were cut into specic shapes for the different
tests. The water absorption of the samples was measured
according to standard GB/T1034. An Instron Corporation 4302
instrument was used to study the stress–strain behavior of the
samples. Dielectric constants were measured on a TH2819A in
a frequency region of 0.1 KHz–100 KHz at 25 ꢀC. Dynamic
mechanical analysis (DMA) was performed on a TA-Q800
apparatus operating in tensile mode at a frequency of 1 Hz
BHPPE-4, BHPPE-6, BHPPE-8 and BHPPE-10 were prepared
by a similar procedure to that used for BHPPE-2. The yields were
as follows: BHPPE-4, 53.1 g (91.3%); BHPPE-6, 57.2 g (93.8%);
BHPPE-8, 59.0 g (92.6%); BHPPE-10, 61.0 g (91.6%).
Characterization
ꢀ
ꢀ
from 40 to 250 C with a heating rate of 5 C min. A parallel
plates rheometer (Bohlin Gemini 200, Britain) was tted with
2.5 cm diameter stainless steel parallel plates. Temperature,
frequency and time sweep tests were performed under a
nitrogen atmosphere. Quantitative information for the melt
ow of the samples could be obtained by recording the
complex viscosities versus temperature, time and shear
frequency during processing. The UL-94 vertical test was per-
formed according to the testing procedure of FMVSS 302/ZSO
3975 with a test specimen bar 127 mm in length, 12.7 mm in
width and about 1.27 mm in thickness. In the test, the poly-
mer specimen was subjected to two 10 s ignitions. Aer the
rst ignition, the ame was removed and the time for the
polymer to self-extinguish (t1) was recorded. Cotton ignition
was noted when polymer dripping occurred during the test.
Aer cooling, the second ignition was performed on the same
sample and the self-extinguishing time (t2) and dripping
characteristics were recorded. The ame test was performed
on ve specimens. If the average t1 plus t2 is less than 10 s
without any dripping, the polymer is considered to be a V-
0 material. If t1 plus t2 is in the range of 10–30 s without any
dripping, the polymer is considered to be a V-1 material.34 The
LOI was determined with an Atlas Limiting Oxygen Index
Chamber. The solubility of the polymers in various solvents
was tested at room temperature (or at the boiling points of the
solvents).
The intrinsic viscosities of BHPPE-(2–10) were obtained at 30 ꢂ
0.1 ꢀC with 0.500 g of polymer dissolved in 100 ml of NMP, using
a Cannon-Ubbelodhe viscometer. The values were obtained by
the one-point method (or Solomon–Ciuta equation):
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
À
Á
2 hsp ꢁ ln hr
hint
¼
C
Where hr ¼ h/h0, hsp ¼ h/h0 ꢁ 1.
The number-average molecular weights (Mn) and weight-
average molecular weight (Mw) were obtained via GPC
Scheme
1 Synthesis routes of semiaromatic difluorobenzamide
monomers and polymers.
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Chemical chain structure of BHPPE-(2–10)
Results and discussion
The chemical structure of the resultant polymers was charac-
terized by FT-IR and 1H-NMR. The FT-IR spectra (Fig. 1) of
polymers exhibited the characteristic ether stretching near 1100
cmꢁ1. The absorptions near 3320 and 1640 cmꢁ1 were attrib-
uted to the amide group. Comparing with the spectra of the
monomers, the characteristic absorption around 1340 cmꢁ1
(C–F) had disappeared. Fig. 2 shows the 1H-NMR spectra of
BHPPE-(2–10). The signals of protons on a benzene ring ranged
from 6.6 to 8.0 ppm. The chemical shis were so close that the
proton peaks could not be distinguished. The signals near 2.12
and 8.5 ppm were assigned to –CH3 and the amide unit. From
Fig. 2 we found that the proton signals shied to high eld with
an increase of carbon numbers of the diamine used in the
reaction. This may be caused by the shielding effects of the
methylene unit. Combined with the FT-IR results, this suggests
that the polymerization proceeded as depicted in Scheme 1.
Synthesis of semiaromatic diuorobenzamide monomers
(BFBE, BFBB, BFBH, BFBO, BFBD)
The synthesis route of monomers is shown in Scheme 1. The
monomers were prepared with a facile interfacial reaction
through a one-step procedure. The reaction temperature in this
procedure could not exceed 30 ꢀC because the reaction was
difficult to control and side-effects could occur, in which case
the resultant product was difficult to purify and the yield was
low.
Chemical structure of monomers
The FT-IR spectra of monomers (ESI Fig. 1†) showed the char-
acteristic absorptions of –CONH– near 3300 and 1630 cmꢁ1. The
characteristic absorption of benzene rings (C–H) was observed
near 3050 cmꢁ1. The aliphatic chain (–CH2–) was observed near
2970 and 2850–2880 cmꢁ1. The absorptions near 1340 cmꢁ1 and
850 cmꢁ1 were attributed to the vibrations of C–F and para-
Tensile properties
1
substituted benzene rings. The H-NMR and 13C-NMR spectra
The average tensile strength values of BHPPE-(2–10) are
summarized in Table 2. As shown in Table 2, the average tensile
strengths of BHPPE-(2–10) were 89–105 MPa. The elongation at
break was in the range 13.2–18.7%. This suggests that BHPPE-
(2–10) have similar mechanical properties to those of the
commercial product PA9T.
of monomers (BFBE) (ESI Fig. 2 and 3†) showed two groups of
peaks ranging from 7.2 to 8.0 ppm that were attributed to the
two proton signals of a benzene ring. The aliphatic chain proton
signals ranged from 1.2 to 3.5 ppm. The signals near 8.5 ppm
were assigned to amide units. Six groups of peaks, C1–C6, were
39.67, 115.23, 129.83, 130.98, 162.54 and 165.41. Combining the
FT-IR and elemental analysis results suggests that the mono-
mers were synthesized as depicted in Scheme 1.
Dynamic mechanical analysis
DMA was carried out to characterize the resulting semiaromatic
polyamides. As shown in Fig. 3, one obvious transition behavior
was observed, dened as the a relaxation. It is well-known that
the glass transition temperature (Tg) of a polymer can be deter-
mined by a relaxation, as it is usually related to the segment
movements in the noncrystalline area.35 The a relaxation
temperatures of these semiaromatic polyamides were found to
be 150.6, 159.5, 171.3, 186.1 and 210.8 ꢀC, respectively. They are
nearly the same as those obtained by the DSC method. The slight
differences are mainly attributed to the different responses of
the polymers to these two measurements. The a-relaxation
temperatures (glass transition temperature) decreased with the
Synthesis of BHPPE-(2–10)
The polycondensation reaction was carried out by nucleophilic
substitution polymerization using potassium carbonate as the
catalyst. The reaction temperature was in the range 160–200 ꢀC.
The purpose of the rst step was mainly to form the bisphenol
salt and dehydrate water (with the azeotropic role of toluene).
This was benecial for obtaining polymers with a large molec-
ular weight. The molecular weights of the polymers were
measured by intrinsic viscosity and GPC. As shown in Table 1,
the hint values of BHPPE-(2–10) ranged from 0.71 to 1.01 dL gꢁ1
,
the Mn and Mw values were in the ranges 6.0 ꢃ 104 to 10.5 ꢃ 104
and 1.26 ꢃ 105 to 2.02 ꢃ 105, respectively. This suggests that
the resultant polyamides had more than 100 repeated units.
The polydispersity indices (PDIs) of polymers were in the range
1.8–2.3.
Table 1 Intrinsic viscosities (hint) and molecular weights of polymers
(BHPPE-(2–10))
Polymers
hint (dL gꢁ1
)
Mn (g molꢁ1
)
Mw (g molꢁ1
)
PDI (Mw/Mn)
BHPPE-2
BHPPE-4
BHPPE-6
BHPPE-8
0.71
0.84
0.95
1.01
6.0 ꢃ 104
7.9 ꢃ 104
9.4 ꢃ 104
1.05 ꢃ 105
8.6 ꢃ 104
1.26 ꢃ 105
1.56 ꢃ 105
1.72 ꢃ 105
2.02 ꢃ 105
1.99 ꢃ 105
2.10
1.97
1.83
1.92
2.31
BHPPE-10 0.89
Fig. 1 The FT-IR spectra of BFBE and polymers (BHPPE-(2–10)).
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Fig. 2 The 1H-NMR spectra of polymers (BHPPE-(2–10)).
Table 2 Thermal and mechanical properties of BHPPE-(2–10) and PA9T
Char yield
(%)
Tensile strength
(MPa)
Young's
modulus (GPa)
Elongation at
break (%)
Storage modulus
at 125 ꢀC (GPa)
Glass transition
Polymers
Tg (ꢀC)
T5% (ꢀC)
temperaturea (ꢀC)
BHPPE-2
BHPPE-4
BHPPE-6
BHPPE-8
BHPPE-10
PA9T
195.6
170.4
156.5
145.6
134.4
115
405
417
441
442
443
464
28.3
7.5
4.1
2.3
0.9
—
97
103
105
94
89
86
2.1
1.9
1.8
1.5
1.1
2.7
14.4
16.7
19.8
18.7
23.2
4.2
1.9
1.6
1.6
1.7
1.4
—
210.8
186.1
171.3
159.5
150.6
—
a
Detected by dynamic mechanical analysis (DMA).
increase in carbon number of the aliphatic chain (methylene) in in Table 3. As shown in Table 3, the water absorptions of
the polymeric backbone. Fig. 4 displays the storage modulus BHPPE-(2–10) were found to be 0.31%, 0.30%, 0.27%, 0.24%
curves of BHPPE-(2–10). As listed in Table 2, the semiaromatic and 0.24%, respectively, which were close to that of the
polyamides exhibited high storage moduli of 2.1, 1.7, 1.8, 1.9 commercial product PA9T (0.17%). The results indicate that
and 1.5 GPa. We also found that the polymers maintained above these semiaromatic polyamides have low water absorption,
the 70% storage modulus (1.5 GPa) at 125 ꢀC compared with that which is good for their dimensional and mechanical stability.
of samples at 40 ꢀC, which indicates that these semiaromatic We also found that the water absorption decreased with
polyamides have excellent mechanical properties.
lengthening of the aliphatic chain of the polyamides. The
main reason was that the high content of methylene group
can improve the hydrophobic property of the semiaromatic
polyamides.
Water absorption
The water absorption of BHPPE-(2–10) was measured
according to standard GB/T1034. The results are summarized
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Thermal properties of BHPPE-(2–10)
The thermal properties of BHPPE-(2–10) were examined by DSC
and TGA. The results are displayed in Fig. 5 and 6, respectively.
As shown in Fig. 5, the Tg values of BHPPE-(2–10) were in the
ꢀ
range 134.4–195.6 C (Table 2). They were higher than that of
ꢀ
commercial products such as PA9T (Tg ¼ 126 C) and copoly-
mers of PA6T (Tg is about 135 ꢀC). Following the decreasing
carbon number of the aliphatic chain, BHPPE-2 exhibited the
ꢀ
highest Tg value (195.6 C) in this series. We did not nd the
melting endothermic peaks from the DSC curves, which
suggests the amorphous nature of the resultant semiaromatic
polyamides. This was different to the other semiaromatic
polyamides reported earlier.28 The main reason was that the
introduction of a large pendent benzene group limited the
locomotion of the molecular chain, so it could not be arranged
in order. As shown in Fig. 6, the initial degradation tempera-
tures (T5%) of BHPPE-(2–10) in nitrogen were 405, 417, 441, 442,
and 443 ꢀC, which are much higher than the glass transition
temperature and close to those of PA9T (Td ¼ 464 ꢀC) and PA10T
(Td ¼ 472 ꢀC). The char yield of BHPPE-(2–4) at 800 ꢀC in
nitrogen was about 28.3% and 7.5%, much higher than that of
PA6T and PA9T. These results suggest that the thermal stability
was almost maintained, with the incorporation of the ether
Fig. 3 The DMA curves (Tan delta) of BHPPE-(2–10).
Fig. 4 The DMA curves (storage modulus) of BHPPE-(2–10).
Dielectric constant
Table 3 summarizes the dielectric constants of BPPPE-(2–10),
which are in the range 3.33–3.68 at 100 kHz. These low dielectric
constants may be attributed to the low polarizability of the C–H
bonds of the alkyl groups and the low water absorption of the
polymers.
Fig. 5 The DSC curves of BHPPE-(2–10) at a heating rate of 10 ꢀC
minꢁ1 in N2.
Table 3 The water absorption and dielectric properties of BHPPE-(2–10) compared to those of PA9T
Dielectric constant
Polymers
Water absorption (%)
Thickness (mm)
0.1 kHz
1 kHz
10 kHz
100 kHz
BHPPE-2
BHPPE-4
BHPPE-6
BHPPE-8
BHPPE-10
PA-9T
0.31
0.30
0.27
0.24
0.24
0.17
1.142
1.130
1.126
1.127
1.125
1.137
4.41
4.33
4.17
4.05
3.96
4.06
4.13
4.07
3.94
3.80
3.75
3.78
3.95
3.82
3.68
3.62
3.54
3.92
3.68
3.56
3.49
3.42
3.33
3.64
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Fig. 7 TGA curves of BHPPE-2 at heating rates of 5 ꢀC minꢁ1, 10 ꢀC
Fig. 6 The TGA curves of BHPPE-(2–10) at a heating rate of 10 ꢀC
minꢁ1, 20 ꢀC minꢁ1, 40 ꢀC minꢁ1 in N2.
minꢁ1 in N2.
Table 4 The maximum thermal degradation temperatures of BHPPE-
(2–10)
linkage and different numbers of methylene units into the
polymeric backbone.
Tmax (ꢀC)
Heating rates BHPPE-2 BHPPE-4 BHPPE-6 BHPPE-8 BHPPE-10
Thermal degradation kinetics
ꢀC min
421
432
452
465
465
472
485
498
468
476
494
513
471
482
501
516
471
483
500
515
The thermal decomposition behavior of these semiaromatic
polyamides was studied with a differential method, the Kis-
singer method, which is the basis of the most powerful methods
for the determination of kinetic parameters. The changes in
thermogravimetric data, caused by variation of the heating rate,
were analyzed. This method can be used to determine the
activation energy of solid state reactions from plots of the
logarithm of the heating rate versus the inverse of the temper-
ature at the maximum reaction rate in constant heating rate
experiments, and does not need a precise knowledge of the
reaction mechanism, using the following eqn (1):
5
10 ꢀC min
20 ꢀC min
40 ꢀC min
ꢀ
ꢁ
ꢂ
ꢃ
h
i
b
AR
E
E
nꢁ1
ln
¼
ln
þ ln nð1 ꢁ amax
Þ
ꢁ
(1)
2
RTmax
Tmax
where b is the heating rate, Tmax is the temperature corre-
sponding to the inection point of the thermal degradation
curves at the maximum reaction rate,
A is the pre-
exponential factor, amax is the maximum conversion, and n
is the reaction order. The activation energy E can be calcu-
lated from the slope of the plot of ln(b/T2max) versus 1000/
Tmax and tting to a straight line. The thermal degradation
curves obtained at different heating rates, 5, 10, 20, 40 ꢀC
minꢁ1, are shown in Fig. 7. The values of the maximum
decomposition rate (Tmax) are shown in Table 4. Fig. 8 shows
the curves of the Kissinger method applied to experimental
data at different heating rates. The activation energy (as
shown in Table 5) of the decomposition of BHPPE-(2–10) was
Fig. 8 Kissinger method applied to eꢁx1perimental data at heating rates
of 5 ꢀC minꢁ1, 10 ꢀC minꢁ1, 20 ꢀC min , 40 ꢀC minꢁ1 of BHPPE-(2–10).
semiaromatic polyamides. This suggests that the long
aliphatic chain is benecial for the thermal stability of these
semiaromatic polyamides. The reaction order (n) can be
calculated by the peak value of the TGA secondary derivative
curves. Then we can obtain the pre-exponential factor (ln A)
value from eqn (1).
calculated from a straight line t of a plot of ln(b/T2
)
max
versus 1000/Tmax. The value obtained from Fig. 8 for the
activation energy (E) of BHPPE-(2–10) was in the range
180.1–275.9 kJ molꢁ1, respectively. The activation energy
increased with lengthening of the aliphatic chain of the
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Table 5 Results of BHPPE-(2–10) according to the Kissinger method
Activation energy
Degradation
order (n)
Pre-exponential
Polymers
E (kJ molꢁ1
)
factor ln A (minꢁ1
)
BHPPE-2
BHPPE-4
BHPPE-6
BHPPE-8
BHPPE-10
180.1
185.9
199.9
203.6
213.4
1.2
2.7
2.3
2.2
2.2
22.9
23.4
23.9
24.5
26.1
Rheological properties of polymers
A parallel plates rheometer was used to study the effects of the
structure of the resulting polyamides on their rheological
properties. As shown in Fig. 9, the complex viscosities of
BHPPE-(2–10) were in the range 32–1890 Pa s at different
temperatures (250–320 ꢀC). We found that when a long aliphatic
chain was introduced into the main chain of the polyamide, the
complex viscosity of the polymer increased, and the longer the
polyamide aliphatic chain, the higher the viscosity. This result
mainly arises because the interactions between molecules
become stronger as the polymer molecular chains become
longer. Consequently, more entangled points should exist, and
the complex viscosity of the polymer melts should get much
higher. Also, we studied the effects of shear frequency (0.01–55
Hz, 290 ꢀC) on the complex viscosities of the resultant poly-
amides (Fig. 10). The viscosities ranged from 94.4 to 1488 Pa s at
different shear frequencies. The melts of these polyamides
exhibited much more stability under high shear rates. In addi-
tion, we found that the complex viscosities of samples which
contained a long aliphatic chain had a much larger change.
This suggests that the sensitivity of the resins to the shear
frequency increases with lengthening the aliphatic chain of the
semiaromatic polyamides. The rheological study (both of
temperature and frequency sweep) revealed that the resultant
semiaromatic polyamides had good processability.
Fig. 10 Plot of complex viscosities versus shear frequency for BHPPE-
(2–10).
Flame retardancy
The LOI values of BPPPE-(2–4) are summarized in Table 6, and
were 34 and 30, respectively. We found that BPPPE-2 had a
larger LOI value than BPPPE-(4–10). Table 6 also lists the UL-94
data for BPPPE-(2–10). The ame retardancy of BPPPE-(2–4)
could reach grades V-1 and V-2, respectively, while the
commercial products such as PA6T and PA9T were combus-
tible. Combing the results of LOI and UL-94 data, we nd that
the introduction of an aromatic ring and short aliphatic chain
into the semiaromatic polyamides chain is benecial for its
ame retardancy. The main reason is that the high content of
char yield formed during combustion of BPPPE-(2–4) segre-
gated the samples from air, so that its ame retardancy was
improved.
Solubilities
Table 7 reports the solubilities of BPPPE-(2–10). These materials
were found to be soluble in strong polar solvents such as NMP,
DMF, and DMSO. They had better solubility than that of PA6T
and PA9T. However, they were insoluble in formic acid, toluene,
1,4-dioxane, HCl, phosphoric acid and so on. Compared to alkyl
polyamides (PA6), BPPPE-(2–10) showed better corrosion
resistance.
Table 6 LOIs and UL-94 data for BHPPE-(2–10)
1st burning
time/s
2nd burning
time/s
UL-94
grade
Sample
LOI
Dripping
BHPPE-2
BHPPE-4
BHPPE-6
BHPPE-8
BHPPE-10
34
30
7.8
18.2
5.6
13.3
No
No
V-1
V-2
Combustible
Combustible
Combustible
Fig.
9 Plot of complex viscosities versus temperature for
BHPPE-(2–10).
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Table 7 Solvent resistance of BPPPE-(2–10) and PA6a
Polymers
Solvents
PA6
BPPPE-2
BPPPE-4
BPPPE-6
BPPPE-8
BPPPE-10
Concentrated sulfuric acid
Formic acid
NMP
+
+
+
+
+
+
+
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
+
+
+
+
+
CF3COOH
+
+
+
+
+
+
HCl (6 mol Lꢁ1
)
ꢁ
+
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
+
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
+
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
+
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢂ
ꢂ
+
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢂ
ꢂ
+
ꢁ
ꢁ
ꢁ
Phosphoric acid
NaOH (1 mol Lꢁ1
Acetone
)
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
Chloroform
DMSO
1,4-dioxane
Toluene
Phenol + tetrachloroethane
a
+: soluble at room temperature; ꢂ: swelling; ꢁ: insoluble with heating.
Conclusions
References
Semiaromatic diuorobenzamide monomers with different
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series of semiaromatic polyamides [BHPPE-(2–10)]. The semi-
aromatic polyamides were prepared by nucleophilic poly-
condensation. The effects of the chemical structure of the
semiaromatic polyamides on the physical performance of the
polymers were investigated in detail. The properties of the
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resultant semiaromatic polyamides are suitable for melting
processes even when the number of repeat units (methylene) in
the aliphatic diamine that reacted with BHPPE is 2. With this
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