Synthesis and characterization of poly(arylene ether sulfone)s with trans-1,4-cyclohexylene ring containing ester linkages

Article abstract of DOI:10.1002/pola.24911

trans-1,4-Cyclohexylene ring containing acid chloride monomers were incorporated into poly(arylene ether sulfone) (PAES) backbones to study their effect on mechanical and thermal properties. The trans-1,4-cyclohexylene ring containing acid chloride monome

Full text of DOI:10.1002/pola.24911

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Synthesis and Characterization of Poly(arylene ether sulfone)s with
trans-1,4-Cyclohexylene Ring Containing Ester Linkages
Bin Zhang, S. Richard Turner
Department of Chemistry, Macromolecules and Interfaces Institute (MII), Virginia Tech, Blacksburg, Virginia 24061
Correspondence to: S. R. Turner (E-mail: srturner@vt.edu)
Received 21 June 2011; accepted 24 July 2011; published online 22 August 2011
DOI: 10.1002/pola.24911
ABSTRACT: trans-1,4-Cyclohexylene ring containing acid chloride
monomers were incorporated into poly(arylene ether sulfone)
(PAES) backbones to study their effect on mechanical and ther-
mal properties. The trans-1,4-cyclohexylene ring containing acid
chloride monomers were synthesized and characterized by NMR
and high-resolution mass spectrum. trans-1,4-Cyclohexylene
containing PAESs were synthesized from the acid chloride
monomers and hydroxyl terminated polysulfone oligomers with
higher molecular weight polymers were obtained. Crystallinity
was promoted in the low molecular weight biphenol-based
PAES samples with the pseudo-interfacial method. The crystal-
linity was confirmed by both the DSC and the wide angle X-ray
diffraction results. The tensile test results of the high molecular
weight polymers suggested that incorporation of the trans-1,4-
cyclohexylene ring containing linkage slightly improved the ulti-
mate elongations while maintaining the Young’s moduli. The
trans-1,4-cyclohexylene ring containing PAESs also showed
a
pseudo-interfacial method and a solution method. These
PAESs, with trans-1,4-cyclohexylene ring containing ester link-
ages, were fully characterized by NMR, thermogravimetric anal-
ysis, differential scanning calorimetry (DSC), size exclusion
chromatography, and dynamic mechanical analysis (DMA). The
tensile properties were also evaluated. The polymers made with
the pseudo-interfacial method had relatively low molecular
weights when compared to the solution method where much
higher sub-Tg relaxations in DMA when compared with their ter-
C
V
ephthaloyl containing analog.
2011 Wiley Periodicals, Inc.
J Polym Sci Part A: Polym Chem 49: 4316–4324, 2011
KEYWORDS: biphenol; bisphenol-A; characterization; poly(ary-
lene ether sulfone)s; polycondensation; polyesters; poly(ether
sulfones); polysulfone-polyester; trans-1,4-cyclohexylene ring
INTRODUCTION Thermoplastic polyarylethers have been
extensively studied since their initial discovery in the early
1960s.1 Poly(arylene ether sulfone)s (PAESs), commonly
known as polysulfones, are important commercial polymers
with wide applications due to their excellent thermal and
mechanical properties.2–5 The literature contains many stud-
ies of PAES structures based on a variety of biphenols (BPs)
and diphenylsulfones. The most common PAES structure is
based on the reaction of bisphenol-A and 4,40-dichloro-
transition around 250 ꢀC was observed with a narrow crys-
tallization window about 30 ꢀC in the BPs-based copolymer
obtained by solution polymerization with terephthaloyl chlo-
ride (TC). Recently, Gaymans and coworkers13 reported their
synthesis of the bisphenol-A-based polysulfone polyester seg-
mented copolymers by using the hydroxyl terminated PAES
oligomer reacted with diphenyl terephthalate in melt or TC
in solution. The reaction parameters, such as the reaction
temperatures and the solvents, were systematically studied;
no mechanical properties, however, were reported.
R
diphenylsulfone. This polymer is commercially sold as UdelV
(Solvay Advanced Polymer LLC). However, some applications
of PAES are limited by drawbacks such as poor resistance to
some solvents, moderate impact resistance, and unacceptable
thermal dimensional changes especially near Tg due to the
PAES amorphous nature.1,6
It is well known that the incorporation of trans-1,4-cyclohex-
ylene rings into a polymer backbone can enhance the me-
chanical properties and affect the crystallization rate.14,15
Poly(1,4-cyclohexylenedimethylene dimethylene terephtha-
late) (PCT) is an important commercial crystalline polyester
and has a fast crystallization rate.14 Increasing the trans/cis
ratio of the cyclohexylene unit enhances the crystallization
rate. Other 1,4-cyclohexylene ring containing polycarbonates
and polyesters, such as poly(1,4-cyclohexylenedimethylene
1,4-cyclohexanedicarboxylate), and poly(butylene 1,4-cyclo-
hexanedicarboxylate), have also been widely reported in the
An important structure modification for property improve-
ment of polysulfone is to incorporate ester segments into
the backbone. There are many reports of the synthesis of
polysulfone polyester segmented copolymers for different
applications with different synthetic methods.7–11 In the
work reported by McGrath and coworkers,12 a glass-crystal
Additional Supporting Information may be found in the online version of this article.
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literature.16–21 However, to the best of our knowledge, there
are no report of trans-1,4-cyclohexylene ring containing
PAESs.
In this article, we describe a systematic study on the effect
of the incorporation of the trans-1,4-cyclohexylene ring con-
taining polyester segments in the PAES backbones. Acid chlo-
ride chemistry which has been widely used in polyarylate
and polyester synthesis.22,23 A series of acid chlorides was
designed and used as the trans-1,4-cyclohexylene ring con-
taining segments to react with the PAES oligomers to yield
the final PAESs with solution polymerization and pseudo-
interfacial polymerization.12 In contrast to the interfacial po-
lymerization technique where the reaction occurs at the
interface, the reaction in pseudo-interfacial polymerization
takes place in the organic phase and the side product is
transferred into the aqueous phase with the assistance of
the phase transfer agent. Two classes of oligomers, bisphe-
nol-A and BP-based PAES oligomers, were chosen. The ther-
mal and mechanical properties of the trans-1,4-cyclohexylene
ring containing PAESs were evaluated by comparing with
their terephthalic analogue and commercially available PAES
FIGURE 1 Structures of the acid chloride monomers.
a rate of 2 ꢀC/min. The DMA parameters are Mode: Multi-
Freq-Strain Tension film; Amplitude: 10 lm; Preload force:
0.01 N. The tensile test was performed on an Instron Model
4400 Universal Testing System with a rate of 2 mm/min at
room temperature. Size exclusion chromatography (SEC) was
used to determine the molecular weights and the molecular
weight distributions. The data were obtained in the SEC sol-
vent at 30 ꢀC on a Waters Alliance model 2690 chromatograph
equipped with a Waters HR 0.5þ HR 2þ HR 3þ HR 4 styragel
column set. Viscotek refractive index detector and a viscome-
ter were used for the molecular weight determination. Poly-
styrene standards were utilized to construct a universal mo-
lecular weight calibration curve. Chloroform and NMP were
used as the SEC solvents with a flow rate of 0.500 mL/min.
The high-resolution mass spectrum (HRMS) was obtained
from an Agilent LC/MS (liquid chromatography/mass spec-
trometry) mass spectrometer with a time of flight analyzer.
The wide-angle X-ray diffraction was performed using a
Rigaku S-Max 3000 3 pinhole SAXS/wide angle X-ray diffrac-
tion (WAXD) system. The X-ray source is the Cu Ka radiation,
and the wavelength is 0.154 nm. Silver behenate is used to cal-
ibrate the sample-to-detector distance and the sample-to-de-
tector distance is 82.5 mm. The WAXD two-dimensional
images were obtained using an image plate, with an exposure
time of 1 h and analyzed using the SAXSGUI software package.
R
R
UdelV and RadelV R provided by Solvay Advance Polymer. A
complementary study on the molecular dynamics using
solid-state NMR technique was also performed and described
elsewhere.24
EXPERIMENTAL
Materials
All the chemicals were purchased from Aldrich with the
exceptions of trans-1,4-cyclohexane dicarboxylic acid (CHDA)
and trans-1,4-cyclohexane dimethanol (CHDM) which were
R
provided by Eastman Chemical Company. The UdelV and
R
RadelV R samples were provided by Solvay Advanced Poly-
mers. Tetrahydrofuran (THF) was dried by PURE SOLV puri-
fication system from Innovative Technologies. Triethylamine
(TEA), chloroform, N,N-dimethylacetamide (DMAc), and N-
methyl-2-pyrrolidone (NMP) were treated with calcium
hydride then purified by the vacuum distillation and stored
over molecular sieves. All the other reagents were used as
received without further purification.
Instrumentation
The 1H and 13C NMR spectra were obtained by a JEOL 500
(500 MHz) spectrometer at room temperature with chemical
shifts relative to tetramethylsilane (TMS). The FTIR data
were obtained on an M2004 FTIR spectrometer from MIDAC
Corporation from 400 to 650 cmꢁ1 with a resolution of 4
cmꢁ1. The Tgs and Tms were determined by differential scan-
ning calorimetry (DSC). The data were obtained by using a
TA InstrumentsTM Q2000. Nitrogen was used as the carrier
gas with a sample flow rate of 20 mL/min and a heating
rate of 10 ꢀC/min. The Tgs were determined in the second
heatiꢀng cycle after the samples were quenched at nominally
100 C/min during the cooling cycle. The thermogravimetric
analysis was carried out by a TA InstrumentsTM Q10 from 25
Monomer Synthesis
The structures and the abbreviations of the trans-1,4-cyclo-
hexylene ring containing acid chloride monomers are shown
in Figure 1. TC is commercially available and used as the
aromatic analog.
Synthesis of trans-1,4-Cyclohexanedicarbonyl Chloride
The glassware and the stir bar were predried in an oven at
80 ꢀC for 12 h. To a 250-mL three-necked round-bottom
flask equipped with a Teflon-coated magnetic stir bar, a con-
denser and an argon inlet, 16.00 g (93.02 mmol) of CHDA,
120.0 mL of thionyl chloride, and 0.1 mL of N,N-dimethylfor-
mamide (DMF) were added. The reaction was stirred in the
presence of argon at 60 C for 4 h. Then the excess amount
of thionyl chloride was distilled out at 60 ꢀC with vacuum.
The white crystals were obtained and dried in vacuum oven
ꢀ
ꢀ
ꢀ
to 600 C under nitrogen at a heating rate of 10 C/min. The
dynamic mechanical analysis (DMA) was performed on a TA
InstrumentsTM Q800 in nitrogen from ꢁ150 to 200 ꢀC with
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1H NMR (CDCl3, ppm): d 8.18 (m, 8H), d 4.22 (d, 4H), d 1.96
(d, 4H), d 1.84 (s, 2H), d 1.18 (m, 4H). 13C NMR (DMSO-d6,
ppm), d 168.0, 165.2, 136.7, 136.2, 131.3, 130.0, 70.5, 37.2,
29.0. HRMS (m/z) Calcd for C24H22O6Cl2: 476.0793; Found:
476.0762; Diff: ꢁ6.70 ppm.
Synthesis of trans-1,4-Cyclohexane-diylbis(methylene)
bis(4-(chlorocarbonyl)cyclohexanecarboxylate)
The compound trans-1,4-cyclohexane-diylbis(methylene)
bis(4-(chlorocarbonyl)cyclohexanecarboxylate) (CCC) was
synthesized in a similar way as compound TCT shown above.
trans-Cyclohexane-1,4-diylbis(methylene))bis(oxy))bis(carbo-
nyl))cyclohexane dicarboxylic acid was obtained as white
powder with a yield of 50.9%. No melting point was
observed due to thermal decomposition below melting point.
SCHEME 1 Synthesis of the bis-A-based and biphenol-based
PAESs.
1H NMR (CDCl3, ppm): d 3.89 (d, 4H), d 2.5–d 1.0 (m, 30H).
13C NMR (CDCl3, ppm), d 177.0, 175.3, 68.9, 42.3, 42.2, 37.2,
28.8, 28.2, 26.1. HRMS (m/z) Calcd for C24H36O8: 452.2410;
Found: 452.2429; Diff 4.14 ppm.
(ꢁ80 kPa) at room temperature for 12 h and then kept
under argon atmosphere. The product was used directly in
the next step without any further purification. Yield 94.4%.
No melting point was observed due to instability.
1H NMR (CDCl3, ppm): d 2.73 (m, 2H), d 2.30 (m, 4H), d 1.58
(m, 4H). 13C NMR (CDCl3, ppm): d 188.4, 50.6, 30.0.
CCC was obtained with a yield of 95.7% and used directly in
the next step without any further purification. No melting
point was observed due to instability.
Synthesis of trans-1,4-Cyclohexane-diylbis(methylene)
bis(4-(chlorocarbonyl)benzoate)
1H NMR (CDCl3, ppm): d 3.84 (d, 4H), d2.5–d 1.0 (m, 30H).
13C NMR (CDCl3, ppm), d 175.7, 175.2, 69.0, 51.9, 42.1, 37.2,
About 10.00 g (49.26 mmol) of terephthaloyl chloride (TC)
was dissolved in 80.0 mL dry THF in a three-necked round-
bottom flask with a magnetic stir bar, an addition funnel and
an argon inlet. A dry THF solution of 1.773 g (12.32 mmol)
of trans-1,4-CHDM and 4.975 g (49.26 mmol ) TEA was
added dropwise in a period of 1 h. The reaction mixture was
stirred at room temperature for 12 h. Then excess water and
TEA were added until a clear solution was obtained. After
acidification, filtration was applied. The solid obtained was
extracted with 600 mL of methanol twice and dried in a vac-
uum oven (ꢁ80 kPa) at 80 ꢀC for 12 h. The white solid
obtained after drying was identified as trans-1,4-cyclohex-
ane-bis(methylene)bis(oxy)bis(oxomethylene) dibenzoic acid
with a yield of 59.6%. No melting point was observed due to
thermal decomposition below melting point.
28.2, 28.1, 26.0. HRMS (m/z) Calcd for
488.1732; Found: 488.1720; Diff: ꢁ2.52 ppm.
C24H34O6Cl2:
Polymer Synthesis
Synthesis of Hydroxyl-terminated PAES Oligomers with
Controlled Molecular Weight
The reaction scheme is shown in Scheme 1. The hydroxyl-
terminated bisphenol(bis-A) and the BP-based PAES oligom-
ers with 2.0 kg/mol target molecular weight were synthe-
sized by using the stoichiometry imbalance technique based
on the Carothers equation. The bis-A-based PAES oligomer
with 2.0 kg/mol target molecular weight is shown as an
example. The BP-based oligomer was synthesized in a similar
fashion. 5.036 g (17.54 mmol) of dichlorodiphenyl sulfone,
5.000 g (21.90 mmol) of bis-A, 7.870 g (56.95 mmol) of
K2CO3, 80.0 mL of DMAc, and 40.0 mL of toluene were
added to a flask equipped with a mechanical stirrer, an ar-
gon inlet and a Dean-Stark trap. The reaction was heated to
140 ꢀC for 3 h to remove water by azeotropic distillation.
Then toluene was distilled out by increasing the temperature
slowly to 160 ꢀC in 2 h. After 20 h at 160 ꢀC, the reaction
mixture was cooled to room temperature. White solid was
obtained by the precipitation of the reaction mixture in a 5
wt % of HCl aqueous solution and filtration. The product
was thoroughly washed three times with 200-mL deionized
water and methanol respectively. After drying at 120 ꢀC for
12 h in vacuum oven (ꢁ80 kPa), the product was obtained
with a yield of 92.4%.
1H NMR (DMSO-d6, ppm): d 13.35 (s, 2H), d 8.07 (s, 8H), d
4.15 (d, 4H), d 1.85 (d, 4H), d 1.75 (s, 2H), d 1.13 (m, 4H).
13C NMR (DMSO-d6, ppm), d 167.2, 165.7, 135.5, 133.8,
130.2, 129.9, 70.2, 37.1, 28.8. HRMS (m/z) Calcd for
C24H24O8: 440.1471; Found: 440.1469; Diff: 0.51 ppm.
The glassware and stir bar were predried in an oven at 80
ꢀC for 12 h. To a 250-mL three-necked round-bottom flask
equipped with a Teflon coated magnetic stir bar, a condenser
and an argon inlet, 2.000 g trans-1,4-cyclohexane bis(methy-
lene) bis(oxy) bis(oxomethylene)dibenzoic acid, 120.0 mL of
thionyl chloride, and 0.1 mL of DMF were added. The reac-
tion was stirred in the presence of argon at 60 ꢀC for 4 h.
Then the excess amount of thionyl chloride was distilled out
at 60 C with vacuum. The fresh product (trans-1,4-cyclohex-
1H NMR (CDCl3, ppm): d 8.18 (m, 16.38), d 7.21 (m), d 7.06
(m), d 6.96 (m), d 6.91 (m), d 6.72 (m, 4.00), d 1.66 (m). In
the proton NMR, the integration area ratio between the pro-
tons with the chemical shift of d 6.72 and d 8.18 was used
to determine the number average molecular weights.
ꢀ
ane-diylbis(methylene) bis(4-(chlorocarbonyl)benzoate, TCT)
was used directly in the next step without any further purifi-
cation. A light yellow solid with a yield of 97.6% was
obtained. No melting point was observed due to instability.
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SCHEME 2 Synthesis of the trans-1,4-cyclohexylene ring containing PAES.
The actual molecular weights of the oligomers were very
close to the target. For the bis-A PAES oligomer, the number
average molecular weight was 2.0 kg/mol from the 1H NMR
end group analysis.
chloroethane was used as the solvent. A typical polymeriza-
tion for the copolymers is described below. 3.015 g (1.478
mmol) bis-A-based PAES oligomer was dissolved in 20.0 mL
of chloroform with addition of 0.373 g (3.695 mmol) TEA in
a two-necked round bottom flask equipped with an argon
inlet. Under vigorous stirring, 0.300 g (1.478 mmol) tereph-
thaloyl chloride in 20.0 mL chloroform was added slowly in
1 h. A viscous solution was obtained after the reaction was
performed at room temperature for another 8 h. After pre-
cipitation in methanol and filtration, the polymer was
washed three times with 100 mL water and 100 mL metha-
nol, respectively, to remove TEA hydrochlorides. With a yield
Synthesis of the High Molecular Weight Bis-A-Based and
Biphenol-based PAESs
Bis-A-based and BP-based PAESs were both synthesized with
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comparable molecular weights to the UdelV, RadelV R samples
and used as our lab-synthesized polymer controls in the
thermal and the mechanical property evaluation. These high
molecular weight samples were synthesized in the same way
as the hydroxyl-terminated PAES oligomers shown above but
with a different stoichiometry imbalance to control the mo-
lecular weights.
ꢀ
of 91.9%, the solid product was dried at 120 C in a vacuum
oven (ꢁ80 kPa) for 12 h.
Polymer Film Preparation
Synthesis of the trans-1,4-Cyclohexylene Ring-Containing
PAES
The film samples were obtained by the solution casting
method. The solid polymer sample was dissolved at room tem-
perature under stirring in chloroform, DMAc, or NMP depend-
ing on the results of solubility test to offer a homogeneous so-
lution with concentration of 10% wt. After the filtration
through a 45-lm microglass fiber filter, the polymer solution
was cast on a leveled glass substrate dried at 80 ꢀC for 12 h
and subsequently dried at 120 ꢀC under vacuum (ꢁ80 kPa)
for 12 h. The dog bone samples for the mechanical property
evaluation were prepared from the polymer films. The dimen-
sion parameters of the dog bone sample were 4.00 mm in
width and about 15 mm in length. The thickness of the sam-
ples was in the range of 60–100 lm. The polymers offered
transparent tough films with no color or light yellow color.
The trans-1,4-cyclohexylene ring containing PAES (Polymer 3
in Scheme 2) polymers were synthesized from the PAES
oligomers and the diacid chloride monomers by pseudo-
interfacial polymerization and solution polymerization.
Pseudo-Interfacial Polymerization
A typical polymerization for the copolymers is described
below. 3.015 g (1.478 mmol) bis-A-based PAES oligomer was
dissolved in 20.0 mL of chloroform in a two-necked round-
bottom flask equipped with an argon inlet. Then a 5.0-mL
aqueous solution of 1.020 g (7.389 mmol) K2CO3 was added
along with 0.038
g (0.150 mmol) tetraethylammonium
iodide (TEAI) which worked as the phase transfer reagent.
Under vigorous stirring, 0.300 g (1.478 mmol) terephthaloyl
chloride in 20.0 mL chloroform was added. The reaction mix-
ture was stirred at room temperature for 8 h. After precipi-
tation in methanol and filtration, the polymer was washed
three times with 100 mL water and 100 mL methanol,
respectively. With a yield of 81.2%, the solid product was
RESULTS AND DISCUSSION
Solubility Results of the trans-1,4-Cyclohexylene
Containing PAES
Solubility tests were performed at room temperature in chlo-
roform, DMSO, DMAc, and NMP. The bis-phenol A-based poly-
mers were readily dissolved in all the solvents listed. BP-
based polymers showed low solubility in chloroform and
DMSO and were soluble in DMAc and NMP. No solubility dif-
ferences were found between the trans-1,4-cyclohexylene-
ꢀ
dried at 120 C in a vacuum oven (ꢁ80 kPa) for 12 h.
Solution Polymerization
High molecular weight materials were prepared with the so-
lution method when dry chloroform or dry 1,1,2,2-tetra-
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monomers which are highly reactive. No melting points were
observed for both the diacid monomers and diacid chloride
monomers because they degrade below melting point.
The Bis-A and BP-Based trans-1,4-Cyclohexylene Ring
Containing PAES by Pseudo-Interfacial Polymerization
The bis-A and BP-based trans-1,4-cyclohexylene ring contain-
ing PAES polymers were synthesized from the PAES oligomers
with 2.0 kg/mol target number average molecular weights
and the diacid chloride monomer (structures shown in Fig. 1)
at stoichiometry ratio. In pseudo-interfacial polymerization,
the reaction took place in the organic phase and the side
product HCl was transferred across the interface with the as-
sistance of the phase transfer reagent TEAI. The polymer sam-
ples were characterized with FTIR. The appearance of the
peak at 1,738 cmꢁ1 which is a characteristic peak of an ester
carbonyl group showed up in the polysulfones containing
ester linkages; while in the polysulfone oligomer samples, no
peak was observed in this wavenumber range (shown in the
supplemental material). This result combined with the
disappearance of the hydroxyl characteristics IR peak at
3,455 cmꢁ1 in the bis-A PAES with the ester segments con-
firmed the formation of the ester linkage and the successful
polymerization. The molecular weight results shown later in
this article also confirmed the successful polymerization. The
1
samples were characterized by H NMR in order to determine
the trans-1,4-cyclohexylene ring conformation in the polymer
backbone. A typical 1H NMR spectrum of the trans-1,4-cyclo-
hexylene ring containing PAES is shown in Figure 2 with the
polymer structure. The enlarged area in the middle of Figure
2 shows the peak of the protons A which are the cyclohexyl
protons next to the carbonyl groups. Only one signal (broad-
ened by multiple splitting) was observed for proton A which
indicated that no isomerization reaction occurred during the
polymerization. Isomerization was not expected as the poly-
merizations were designed to be performed at low
temperatures.
SCHEME 3 Synthesis of the trans-1,4-cyclohexane bis(methy-
lene) bis(4-(chlorocarbonyl)benzoate) (TCT).
containing and the 1,4-phenyl-containing polymers in the
solvents studied.
Synthesis of trans-1,4-Cyclohexylene Ring-Containing
Diacid Chloride Monomers
Terephthaloyl chloride is commercially available and was
used as the aromatic analogue. The 1,4-cyclohexanedicar-
bonyl chloride (CHDC) monomer (structure shown in Fig. 1)
was obtained from the high conversion reaction of trans-
CHDA with thionyl chloride.
The molecular weights and the thermal properties of the
pseudo-interfacial polymerization products were characterized
(summarized in Table 1). All the polymer samples were dried
in a vacuum oven thoroughly before characterization. Inde-
pendent of polysulfone oligomer used, pseudo-interfacial poly-
merization yielded polymers with the number average molec-
ular weights lower than 10 kg/mol. The polydispersity values
of the polymers were all lower than the ideal value of 2.0.
The low-polydispersity results from the loss of some low mo-
lecular weight fractions during the precipitation isolation pro-
cedure. In both bis-A PAES and BP PAES series, the terephtha-
loyl containing polymers (Bis-A_TC and BP_TC) had the
highest glass transition temperatures. With the incorporation
of the trans-1,4-cyclohexylene ring, the glass transition tem-
perature decreased in the monomer sequence of CHDC > TCT
> CCC. This Tg trend was as expected because the cyclohexy-
lene ring incorporated in the polymer backbone can provide
flexibility and facilitate the chain segment motion resulting in
a decreased Tg. The bisphenol-A containing PAES polymers
did not show melting transitions due to the tetrahedral iso-
propylidene units.
In the synthesis of the new TCT and CCC trimer diacid chlo-
ride monomers, the corresponding diacid monomers were
first synthesized by using an excess amount of terephthaloyl
chloride (in case of TCT) or CHDC (in case of CCC). The syn-
thesis scheme of TCT is shown in Scheme 3 as an example.
After hydrolysis and acidification, the excess of terephthaloyl
chloride ensured that only the trimer diacid monomer was
formed in the first step with the terephthalic acid. The diacid
monomer mixtures required a purification step to obtain the
pure trimer diacid compound. This was accomplished by
extraction twice with 600 mL methanol to remove the ter-
ephthalic acid. The obtained diacid monomer structures
were confirmed by 1H NMR, 13C NMR, and HRMS. With the
subsequent treatment of the trimer diacid with thionyl chlo-
ride, the desired trimer diacid chlorides TCT and CCC were
obtained. This synthetic route was designed due to the diffi-
culty to fully characterize the TCT and CCC diacid chloride
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FIGURE 2 1H NMR spectrum of a typical trans-1,4-cyclohexylene ring containing PAES.
When the bis-A PAES oligomers were replaced by the BP
PAES oligomers, crystallinity was found in all four polymer
samples. Independent of the acid chloride monomers, the
melting transitions of the polymers were all in the vicinity of
240 ꢀC. The melting transition data of the BP_TC sample is
in close agreement with the reported value.12 The DSC melt-
ing transition results were further confirmed by the WAXD
measurements. All four BP-based PAESs showed similar
WAXD pattern. An example pattern of BP_TC is shown in Fig-
ure 3. Similar to the bis-A system, decreasing glass transition
temperatures in the monomer sequence of TC > CHDC >
TCT > CCC were found. Because of the structure independ-
ency of the melting transition, the decreasing glass transition
temperatures enlarged the crystallization window defined as
the temperature difference between Tg and Tm (shown as DT
in Table 1). The DSC curve of samples BP_CCC is shown in Fig-
ure 4 with a crystallization window of 77 ꢀC. In the DSC study,
the samples were quenched at nominally 100 ꢀC/min or
ꢀ
cooled at a rate of 2 C/min in the cooling cycles. It needs to
be noted that independent of the cooling rate, neither recrys-
tallization nor melting transition were observed in the cooling
cycle and the second heating cycle of the DSC curves in all the
polymers. These results indicated that the semicrystallinity
was a result of the solvent-induced crystallization with rela-
tively low molecular weight samples. A slow crystallization
rate in the melt inhibits polymer recrystallization.
TABLE 1 Molecular Weights, Tgs and Tms of the Bis-A and BP
Based trans-1,4-Cyclohexylene Ring Containing PAES by
Pseudo-Interfacial Polymerization
Molar
Mass
(kg/mol)
Polymers
Mn
Mw
PDI
Tg (ꢀC)
Tm (ꢀC)
DT (ꢀC)
Bis-A_TC
Bis-A_CHDC
Bis-A_TCT
Bis-A_CCC
BP_TC
11.5
10.5
6.9
22.7
16.3
10.9
17.4
9.2
1.9
1.5
1.6
1.6
1.5
1.6
2.1
1.3
182
168
160
155
200
186
177
167
–
–
–
–
–
–
10.8
6.2
–
–
247
244
241
244
47
48
64
77
BP_CHDC
BP_TCT
5.2
8.4
3.6
7.7
FIGURE 3 Small-angle X-ray diffraction pattern of the BP_TC
BP_CCC
4.2
5.6
sample.
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DMAc/Chloroform were used. In agreement with a previous
report,13 in our system, the solvents listed above resulted in
low molecular weight products probably due to a small
amount of water which hydrolyzed some of the diacid chlo-
ride and disrupted the stoichiometry balance. Successful so-
lution polymerization was obtained in 1,1,2,2-tetrachloro-
ethane which provided good solubility to the starting
materials and the products. The polymer products from solu-
tion were also characterized by FTIR and 1H NMR. The
results were similar to the results from the polymers by
pseudo-interfacial polymerization as shown earlier. The suc-
cessful polymerization was confirmed by the appearance of
the ester carbonyl peak in the FTIR of the products. The
trans-1,4-cyclohexylene ring conformation was confirmed by
the 1H NMR peak of the cyclohexyl protons next to the car-
bonyl groups.
FIGURE 4 DSC curves of the BP based trans-1,4-cyclohexylene
ring containing PAES synthesized from CCC(BP_CCC sample).
The molecular weights and thermal properties of the poly-
mer products with solution polymerization are summarized
in Table 2. For both of the bis-A- and BP-based PAES, the
solution method yielded polymers with higher molecular
weights than those from the pseudo-interfacial polymeriza-
tion. The molecular weights of cyclohexylene ring containing
polymers were comparable to the molecular weight of the
The Bis-A and BP-Based trans-1,4-Cyclohexylene Ring
Containing PAES by Solution Polymerization
Attempts to cast films from the trans-1,4-cyclohexylene
ring containing polymers prepared by pseudo-interfacial po-
lymerization resulted in brittle films due to the low molecu-
lar weights. In order to obtain high quality films for the
mechanical property characterizations, trans-1,4-cyclohexy-
lene ring containing PAESs were prepared from solution by
using the same starting materials at stoichiometry ratio. For
the bisphenol-A series, chloroform was chosen, because it is
easy to dehydrate and the oligomer and the product are
both soluble. Chloroform was not used for the BP series,
because the solubility of the starting oligomer is very low to
provide a high concentration for the solution polymerization.
Furthermore, the solubility of the polymer product is limited.
Different solvent systems including DMAc, DMF, NMP, and
R
R
UdelV and RadelV R controls so that the mechanical proper-
ties of those polymers were evaluated without having molec-
ular weight as a factor. The SEC traces of the polymers from
the solution method were all observed with monomodal
peaks with no sign of branching or crosslinking. No crystal-
linity was found in the BP-based PAES samples listed in
Table 2. As the repeat unit structures are the same for the
samples with the pseudo-interfacial and solution polymeriza-
tion, the loss of crystallinity could be due to the combination
of higher molecular weights and slightly larger PDIs (Poly-
dispersity Index) with the solution method compared to
those with the pseudo-interfacial methods. The fact that
TABLE 2 Molecular Weights, Tgs, and Tms of the Bis-A and BP
Based trans-1,4-Cyclohexylene Ring Containing PAES by
Solution Polymerization with Controls
TABLE 3 Tensile Test Results of the Bis-A and BP Based trans-
1,4-Cyclohexylene Ring Containing PAES by Solution
Polymerization with Controls
Molar
Mass
(kg/mol)
Polymers
Modulus (MPa)
Strain at Failure (%)
a
Polymers
Mn
Mw
PDI
Tg (ꢀC)
Tm (ꢀC)
Td (ꢀC)
R
UdelV control
1304 6 86
N/Aa
6.4 6 0.5
N/A
R
UdelV
22.8
20.8
24.6
23.2
11.0
9.6
41.7
36.0
49.9
36.1
28.7
18.4
28.8
37.4
32.5
24.7
17.8
28.9
1.8
1.7
2.0
1.5
2.6
1.9
2
189
186
189
181
163
159
220
227
220
211
196
185
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
498
537
480
466
429
450
526
565
541
497
448
469
Bis-A PAES
Bis-A_TC
BisA PAES
Bis-A_TC
1550 6 106
1504 6 108
1318 6 73
1417 6 169
1353 6 92
1498 6 140
1758 6 137
1175 6 92
1216 6 100
1329 6 315
15.4 6 3.9
13.9 6 3.6
17.5 6 8.6
14.4 6 2.4
8.1 6 1.3
7.9 6 0.8
8.4 6 0.8
34.9 6 11
8.2 6 1.2
9.9 6 1.5
Bis-A_CHDC
Bis-A_TCT
Bis-A_CCC
Bis-A_CHDC
Bis-A_TCT
Bis-A_CCC
R
RadelV R control
R
RadelV R
14.2
21.6
10.8
9.3
BP PAES
BP_TC
BP_CHDC
BP_TCT
BP_CCC
a
BP PAES
BP_TC
BP_CHDC
BP_TCT
BP_CCC
a
1.7
3.0
2.6
2.1
2.7
8.6
10.5
N/A, not available, the sample resulted in brittle film in solution
casting.
5 % weight loss temperature in nitrogen.
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ture relaxation suggested that the incorporation of the trans-
1,4-cyclohexylene ring can potentially enhance the impact
strength without sacrificing modulus.
CONCLUSIONS
The incorporation of the trans-1,4-cyclohexylene rings into a
polymer backbone is well known to have a dramatic influence
on the polymer properties such as crystallinity, thermal, and
mechanical properties. In this article, trans-1,4-cyclohexylene
ring units were successfully introduced into the PAES back-
bones by the reactions of a series of diacid chloride mono-
mers and the hydroxyl-terminated PAES oligomers. Crystallin-
ity was achieved in the BP-based trans-1,4-cyclohexylene ring
containing PAESs with the pseudo-interfacial method but not
in the bisphenol-A-based polymers. Recrystallization was not
observed in the second heating cycle of the DSC measurement
likely due to the slow crystallization rate of the copolymer in
the melt state. The mechanical properties of the high molecu-
lar weight trans-1,4-cyclohexylene ring polymers from the so-
lution polymerization were evaluated. Both the tensile proper-
ties and the DMA results suggested that the incorporation of
trans-1,4-cyclohexylene ring ester linkages improves the ulti-
mate elongation and promotes sub-Tg relaxations while main-
taining the moduli of the polymers.
FIGURE 5 DMA curves of the bis-A-based trans-1,4-cyclohexy-
lene ring containing PAES and its aromatic analogue.
higher molecular weight results in lower crystallinity has
been reported in polymer such as polyethylene and polye-
theretherketone.25–27 Similar to the results in the pseudo-
interfacial polymerization, in both series, the terephthaloyl
containing polymers had the highest glass transition temper-
atures and the glass transition temperature decreased in the
sequence of TC > CHDC > TCT > CCC as expected.
This research was sponsored by the Army Research Laboratory
and was accomplished under Cooperative Agreement Number
W911NF-06-2-0014. The views and conclusions contained in
this document are those of the authors and should not be inter-
preted as representing official policies, either expressed or
implied, of the Army Research Laboratory or the U.S. Govern-
ment. The U.S. Government is authorized to reproduce and dis-
tribute reprints for Government purposes notwithstanding any
copyright notation hereon. The authors acknowledge the assis-
tance of the Department of Chemistry and the Macromolecules
and Interfaces Institute at Virginia Tech. The authors are grate-
ful to Solvay Advanced Polymers L.L.C. and Eastman Chemical
Company for supplying chemicals. The authors appreciate the
assistance of Professor Long’s, Professor Riffle’s, and Professor
McGrath’s groups at Virginia Tech. The authors also appreciate
assistance from Professor Moore’s group at Virginia Tech for
WAXD measurements on the Rigaku S-Max 3000 3 pinhole
SAXS/WAXD system from NSF DMR-0923107.
The bis-A-based and BP-based PAESs were both synthesized
R
R
with comparable high molecular weights to the UdelV, RadelV
R samples and used as our lab-synthesized polymer controls
in mechanical property evaluation. The film tensile test
results, summarized in Table 3, suggested that the trans-1,4-
cyclohexylene ring containing PAES exhibited approximately
the same Young’s moduli as their aromatic analogue and the
property controls. Moderate ultimate elongation improve-
ments were observed in the trans-1,4-cyclohexylene ring con-
taining polymers. This result is in agreement with a similar
moderate elongation enhancement in trans-1,4-cyclohexylene
containing polyketone polysulfone previously published.28
In the DMA tests, the trans-1,4-cyclohexylene ring containing
PAES showed a higher relaxation, with the peak temperature
value in the vicinity of ꢁ70 ꢀC, than their aromatic analog.
Typical DMA curves of the trans-1,4-cyclohexylene containing
PAES and the terephthaloyl containing PAES are shown in
Figure 5. The enlarged area is the DMA low ꢀtemperature
region. At the peak value in the vicinity of ꢁ60 C, the trans-
1,4-cyclohexylene ring containing PAES showed a large low-
temperature relaxation which was absent in the aromatic
analogue. The observed sub-Tg relaxation has been well
reported in the literature. Similar relaxations were observed
in a series of 1,4-cyclohexylene ring containing polyesters
with a peak value at around ꢁ55 ꢀC.17 In the secondary
relaxation study reported by Chen and Yee,15 a low-tempera-
ture relaxation with the peak value about ꢁ75 ꢀC was
observed in PCT. On the basis of the references, we propose
that the origin of the secondary relaxations in our PAESs
samples is the conformation transition of the backbone
trans-1,4-cyclohexylene ring.29 This enhanced low-tempera-
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