Soluble, semi-crystalline PEEK analogs based on 3,5-difluorobenzophenone: Synthesis and characterization

Article abstract of DOI:10.1016/j.polymer.2012.03.056

The solubility and thermal properties of poly(ether ether ketone) (PEEK) have been modified by utilizing various ratios of the traditional electrophilic component, 4,4′-difluorobenzophenone, 1, utilized to synthesize PEEK and a comonomer, 3,5-difluorobenzophenone, 2, which is simply a geometric isomer of 1. The resulting polymers ( m-PEEK ) have the same chemical composition as PEEK, allowing for accurate structure-property relationships to be determined. The thermal properties were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The ratio of monomer 1 to monomer 2 had a dramatic influence on the thermal properties and solubility characteristics of PEEK. At higher ratios, 90:10, 85:15, and 80:20, the materials were semi-crystalline and their solubility was very limited in solvents such as N-methyl-pyrrolidinone (NMP) while at lower ratios, 75:25 and 50:50, the PEEK derivatives were completely amorphous and soluble in NMP. TGA analysis indicated excellent thermal stability as most of the materials displayed 5% weight loss temperatures (T_d-5%) greater than 450 °C.

Full text of DOI:10.1016/j.polymer.2012.03.056

Polymer 53 (2012) 2327e2333
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Polymer
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Soluble, semi-crystalline PEEK analogs based on 3,5-difluorobenzophenone:
Synthesis and characterization
*
Andria Fortney, Eric Fossum
Department of Chemistry, Wright State University, 202 Oelman Hall, 3640 Colonel Glenn Highway, Dayton, OH 45435, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The solubility and thermal properties of poly(ether ether ketone) (PEEK) have been modified by utilizing
various ratios of the traditional electrophilic component, 4,40-difluorobenzophenone, 1, utilized to
synthesize PEEK and a comonomer, 3,5-difluorobenzophenone, 2, which is simply a geometric isomer of
1. The resulting polymers (“m-PEEK”) have the same chemical composition as PEEK, allowing for accurate
structureeproperty relationships to be determined. The thermal properties were investigated by ther-
mogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The ratio of monomer 1 to
monomer 2 had a dramatic influence on the thermal properties and solubility characteristics of PEEK. At
higher ratios, 90:10, 85:15, and 80:20, the materials were semi-crystalline and their solubility was very
limited in solvents such as N-methyl-pyrrolidinone (NMP) while at lower ratios, 75:25 and 50:50, the
PEEK derivatives were completely amorphous and soluble in NMP. TGA analysis indicated excellent
thermal stability as most of the materials displayed 5% weight loss temperatures (Td-5%) greater than
450 ꢀC.
Received 12 January 2012
Received in revised form
22 March 2012
Accepted 24 March 2012
Available online 3 April 2012
Keywords:
Poly(arylene ether)s
Copolymer
Crystallinity
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
developed NAS reactions that involve displacement of aryl fluo-
rides, which are activated by the presence of strong electron
Due to their excellent mix of properties poly(arylene ether)s,
PAEs, are widely used as engineering thermoplastics [1,2]. Poly(-
ether ether ketone), PEEK, is a semi-crystalline polymer consisting
of para linked phenyl and benzophenone units (Fig. 1) [3e5]. PEEK’s
structure and its semi-crystalline nature provide excellent
mechanical properties, thermooxidative stability, and solvent
resistance, however, its solubility is generally limited to harsh
solvents such as concentrated sulfuric acid. Thus, the processing of
PEEK can be somewhat challenging. A number of methods have
been developed to enhance the solubility and processability of
PEEK including: (1) introduction of functional groups [6e10], (2)
incorporation of comonomers [11e13], (3) disrupting the symmetry
by introducing meta or ortho linked monomer units [4,14e17], and
(4) increasing the number of ether bonds per repeat unit [18].
The synthesis of PEEK is typically achieved via the nucleophilic
aromatic substitution (NAS) reaction of hydroquinone with 4,40-
difluorobenzophenone, 1 [3,5,19]. The reaction is carried out at
extremely high temperatures in order to overcome the solubility
difficulties associated with the resulting polymer. Recently, we have
withdrawing groups located in the meta position [20e22]. The end
result is a PAE in which the NAS activating group is present as
a pendant moiety, rather than being directly incorporated into the
backbone. Essentially, the geometric isomers of many of the more
common PAEs can be prepared as long as the corresponding 3,5-
difluoro aromatic systems are available. For example, a PEEK-like
derivative was prepared from 3,5-difluorobenzophenone, 2, and
bis-(4-hydroxyphenyl) ether (m-PEEEK) [21], which is the
geometric isomer of poly(ether ether ether ketone), PEEEK (Fig. 1)
[18]. While PEEEK is semi-crystalline, the polymer prepared with
3,5-difluorobenzophenone was completely amorphous.
This paper describes efforts to prepare a geometric isomer of the
more well known PEEK and subsequently tailor the crystallinity and
solubility properties by preparing copolymers with varying ratios of
4,40-difluorobenzophenone and 3,5-difluorobenzophenone. The
ultimate goal was to prepare a geometric isomer of PEEK that was
soluble in common organic solvents while maintaining a high level
of crystallinity, but also possessed a site for relatively straightfor-
ward functionalization. For discussion purposes we will refer to
what is essentially the homopolymer of hydroquinone and 3,5-
difluorobenzophenone as meta-PEEK (m-PEEK, Fig. 1) although it
is really an alternating copolymer of 1,3 and 1,4 poly(phenylene
oxide) bearing a pendant benzoyl group at the 5 position of each 1,3
* Corresponding author.
E-mail address: eric.fossum@wright.edu (E. Fossum).
0032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2012.03.056

2328
A. Fortney, E. Fossum / Polymer 53 (2012) 2327e2333
Fig. 1. Structures of PEEK, PEEEK, o-PEEK, m-PEEEK, PPO, and m-PEEK.
phenyl ring. In order to avoid the synthetic challenges associated
with using hydroquinone as the bisphenol component, such as
cyclization and oxidation issues, two isomeric forms of an oligo-
meric bisphenol were utilized, 4,40-bis(4-hydroxyphenoxy)benzo-
phenone, 3 [23], and 3,5-bis(4-hydroxyphenoxy)benzophenone, 4.
The structureeproperty relationships of the resulting polymers
were evaluated through a combination of thermal analysis, solu-
bility, and X-ray diffraction studies.
2.3. 3,5-Bis-(4-hydroxyphenoxy)benzophenone, 4
In a 50 mL RB flask, equipped with a stir bar, DeaneStark trap,
a condenser, and N2 gas outlet, were placed 2.0 g (9.1 mmol) of 3,5-
difluorobenzophenone, 3.41 g (27.5 mmol) of 4-methoxyphenol
and 5.7 g (41.2 mmol) of K2CO3 along with 10 mL of toluene and
14 mL of NMP. The DeaneStark trap was filled with toluene and the
mixture was heated to 150 ꢀC for approximately 4 h to ensure
complete dryness. The toluene was removed and the reaction
temperature was raised to 185 ꢀC for an additional 16 h at which
point the mixturewas cooled toroom temperature. The solutionwas
added dropwise, with vigorous stirring, to dilute aqueous HCl
(300 mL), pH w 4. The organic material was extracted into 200 mL
of toluene. The layers were separated and the organic layer was
dried over MgSO4 and concentrated under reduced pressure to
afford a yellow oil. The oil was then redissolved in 200 mL of toluene
and washed (5ꢁ) with 200 mL of a saturated sodium carbonate
and 300 mL of water (2ꢁ). The toluene layer was then dried over
MgSO4 and concentrated under reduced pressure, yielding a light
yellow oil, which was triturated with 200 mL of distilled water at
90 ꢀC for 6 h, followed by vigorous stirring at room temperature
resulting in 3.44 g (88%) of a yellow solid. The crude material
2. Experimental
2.1. Materials
All reactions were performed under a nitrogen atmosphere and
all transfers were done using syringes or cannula as necessary. N-
methyl-pyrrolidinone, (NMP), HPLC grade (SigmaeAldrich) was
dried over CaH2 and distilled under a nitrogen atmosphere prior to
use. Tetrahydrofuran (THF), ACS grade (VWR), was used as received.
3,5-Difluorobenzophenone, 2, was purchased from Alfa Aesar
and recrystallized from ethanol prior to use. 4,40-difluor-
obenzophenone, 1, was purchased from Oakwood Products, Inc.
Hydrobromic acid (40%) and p-methoxyphenol were purchased
from Sigma Aldrich and used as received. 4,40-Bis-(4-
hydroxyphenoxy)benzophenone, 3, was prepared according to
a literature procedure [23].
was used without any further purification. 1H NMR (DMSO-d6
d):
3.76 (s, 6H); 6.80 (t,1H); 6.83 (d, 2H); 6.99 (d, 4H); 7.10 (d, 4H); 7.52 (t,
2H); 7.66 (m, 1H); 7.72 (m, 2H). GC/MS: m/z: 426.
In a 500 mL RB flask, equipped with a stir bar, reflux condenser,
and N2 gas inlet, were placed 3.44 g (8.1 mmol) of 3,5-bis-([p-
methoxyphenoxy]) benzophenone, 20 mL of 48% hydrobromic acid
and 200 mL of glacial acetic acid. The resulting mixturewas heated to
130 ꢀC for 4 days at which point the solution was allowed to cool to
room temperature and thenpoured into 500 mL of vigorously stirred
distilled water to afford a light brown semi-solid. The organic
material was extracted into 250 mL of chloroform and the layers
were separated. The chloroform layer was thenwashed with 500 mL
of saturated sodium bicarbonate (2ꢁ) and 500 mL of distilled water,
followed by drying over magnesium sulfate. The chloroform was
then removed using a rotary evaporator to afford a yellow oil, which
was dried further under vacuum affording 2.63 g (82%) of a light pink
solid. The crude product was triturated with 50 mL of ethanol:water
solution (50:50) leaving behind a yellow oil, which was redissolved
in 50 mL of chloroform. The chloroform solution was dried over
MgSO4 and concentrated under reduced pressure, followed by
drying under vacuumto afford 1.47 g (45.7%)of a cream colored solid.
2.2. Instrumentation
1H and 13C NMR spectra were obtained using a Bruker AVANCE
300 MHz instrument operating at 300 and 75.5 MHz, respectively.
Samples were dissolved in (dimethylsulfoxide)-d6 or chloroform-
d as required. Size Exclusion Chromatography (SEC) analysis was
performed using a system consisting of a Viscotek Model 270 Dual
Detector (viscometer and light scattering) and a Viscotek Model
VE3580 refractive index detector. Two Polymer Laboratories 5 mm
PL gel Mixed C columns (heated to 40 ꢀC) were used with tetra-
hydrofuran as the eluent and a Thermoseparation Model P1000
pump operating at 1.0 mL/min. Weight average molecular weights,
Mw, were determined using the SEC light scattering detector while
the polydispersity indices were calculated from the RI signal.
Differential Scanning Calorimetry (DSC) analyses were performed
under nitrogen on a TA Instruments Q200 DSC while Thermogra-
vimetic (TGA) analyses were performed under nitrogen and air
atmospheres on a TA Instruments Q500 TGA, at a heating rate of
20 ꢀC/min. X-Ray diffraction data were acquired using a Rigaku-
Miniflex II Desktop X-Ray Diffractometer measured from an angle
1H NMR (DMSO-d6
7.52 (t, 2H); 7.66 (tt, 1H); 7.72 (dd, 2H); 13C NMR (DMSO-d6
d): 6.74 (t, 1H); 6.80 (m, 6H); 6.98 (d, 4H);
d
):
109.0, 110.8, 116.4, 121.4, 128.5, 129.6, 132.9, 136.3, 139.2, 146.7,
154.4, 159.8, 194.5. GC/MS: m/z: 399.
(2
q
) range of 10ꢀe90ꢀ.

A. Fortney, E. Fossum / Polymer 53 (2012) 2327e2333
2329
was stirred at 185 ꢀC for 16 h at which point 0.11 g (0.50 mmol) of
4,40-difluorobenzophenone were added and the mixture was stir-
red at 185 ꢀC for an additional 8 h. The resulting dark brown
solution was diluted with 4 mL of NMP and heated for 2 h further at
150 ꢀC to ensure a homogeneous solution. The NMP solution was
then cooled to room temperature and added dropwise to 200 mL of
vigorously stirred distilled water to afford a light tan solid which
was isolated via filtration, followed by drying under vacuum. The
product was redissolved in NMP and reprecipitated twice, first
using distilled water and finally from isopropanol:water (95:5) to
provide a light tan colored solid, which was isolated via filtration
and dried under vacuum to afford 0.46 g (75%) of an off white solid.
Scheme 1. Synthesis of 3,5-bis(4-hydroxyphenoxy)benzophenone, 4.
2.4. Synthesis of m-PEEK, 5
In a 25 mL RB flask, equipped with a stir bar, reflux condenser,
and N2 gas inlet, were placed 0.29 g (0.72 mmol) of 3,5-bis-(4-
hydroxyphenoxy)benzophenone, 4, and 0.16 g (0.72 mmol) of 3,5-
difluorobenzophenone, 2, along with 1.1 mL of NMP. The resulting
mixture was heated to 185 ꢀC and held there for 48 h. The resulting
dark brown solution was then allowed to cool to room temperature,
followed by diluting with 3 mL of NMP. The polymer solution was
added dropwise to 300 mL of vigorously stirred acidified water (w4
pH) to afford dark brown, fine particulates, which were isolated via
filtration and dried under vacuum to afford 0.33 g (75%) of 5 as
a dark brown solid. The crude material was redissolved in 4 mL of
NMP and precipitated from 250 mL of isopropanol to afford 0.18 g
3. Results and discussion
3.1. Polymer synthesis
Initial attempts to prepare m-PEEK via the reaction of hydro-
quinone and 3,5-difluorobenzophenone, 2, resulted in the forma-
tion of only relatively low molecular weight materials, which
included a high percentage of cyclic species. In order to overcome
this apparent limitation in the synthesis of m-PEEK, an oligomeric
bisphenol species, 3,5-bis(4-hydroxyphenoxy)benzophenone, 4,
was prepared according to the procedure outlined in Scheme 1. It
was anticipated that the use of 4 would hinder the formation of
cyclic species and also lessen the possibility of oxidation of the
hydroquinone structure to a benzoquinoid structure.
(42%) of a dark tan solid. 1H NMR (CDCl3,
d
): 6.78 (b, 1H); 6.96 (b,
6H); 7.32 (m, 2H); 7.45 (m, 1H) 7.68 (m, 2H); 13C NMR (CDCl3,
d
):
112.0,113.9,121.0, 128.6, 130.1,132.8,136.8,140.3, 152.3, 159.0, 195.1.
Reaction of 3,5-difluorobenzophenone, 2, with a slight excess of
4-methoxyphenol under typical NAS conditions (NMP, K2CO3, heat)
provided the corresponding protected bisphenol in good yield.
Deprotection of the phenolic groups was achieved via reaction with
HBr in acetic acid to afford the desired bisphenol, 3,5-bis(4-
hydroxyphenoxy)benzophenone, 4, in good yield. The structure of
4 was confirmed via GC/MS analysis as well as 1H and 13C NMR
spectroscopy.
The synthesis of m-PEEK was then carried out as depicted in
Scheme 2. Reaction of equimolar amounts of 2 and 4, at 185 ꢀC for
48 h, resulted in the formation of m-PEEK, 5, with a weight average
molecular weight, Mw, of 15,600 Daltons (Da). Structural charac-
terization was provided via a combination of 1H and 13C NMR
(Fig. 2a) spectroscopy, which both showed the presence of all of the
anticipated peaks. As expected, m-PEEK was soluble in a variety of
solvents ranging from tetrahydrofuran (THF) and chloroform to
N,N-dimethylacetamide (DMAc). Differential scanning calorimetry
(DSC) indicated that m-PEEK was completely amorphous, with only
a glass transition temperature, Tg, of 105 ꢀC observed in heating
2.5. P50-Alt-m-P50 copolymer using 3,5-bis-(4-hydroxyphenoxy)
benzophenone, 6
The alternating copolymer 6 was prepared according to the
same procedure as utilized for the synthesis of m-PEEK, except that
4,40-difluorobenzophenone, 1, was used in place of 2.
(45% yield). 1H NMR (CDCl3,
d
): 6.83 (t,1H); 6.95, (d, 4H); 7.01, (b,
10H); 7.38 (t, 2H); 7.50 (t, 1H); 7.71 (bd, 6H); 13C NMR (CDCl3,
d):
112.0, 113.9, 117.1, 121.0, 128.6, 130.1, 132.2, 132.3, 132.8, 136.8, 140.3,
152.0, 152.3, 159.0, 161.5, 194.0, 195.1.
2.6. General procedure for copolymers 7(aee)
As an example procedure the synthesis of P75-co-m-P25, 7b, will
be described. In a 25 mL RB flask, equipped with a stir bar,
condenser, and gas inlet were placed 0.40 g (1.0 mmol) of 4,40-
bis(4-hydroxyphenoxy)benzophenone, 3, 0.11 g (0.50 mmol) of 3,5-
difluorobenzophenone, 2, and 1.8 mL of NMP. The resulting mixture
Scheme 2. Synthesis of m-PEEK, 5, and P50-alt-m-P50 Copolymer, 6.

2330
A. Fortney, E. Fossum / Polymer 53 (2012) 2327e2333
Fig. 2. 75.5 MHz 13C NMR spectra (CDCl3) of (a) m-PEEK (5), (b) copolymer 6, and (c) copolymer 7a.
ramps up to 400 ꢀC (see Fig. 3). The somewhat low Tg value,
compared to PEEK (144 ꢀC), is most likely a result of the highly
flexible poly(phenylene oxide), PPO, backbone (Fig. 1, Tg of 95 ꢀC)
and the lack of any crystalline regions. The thermal stability of m-
PEEK was evaluated via thermogravimetric analysis (TGA) and it
was found that the 5% weight loss temperature (Td-5%) was 428 ꢀC,
somewhat less thermally stable than PEEK. However, this might
also be attributed to the lack of any crystallinity in m-PEEK.
To explore the impact of incorporating m-PEEK segments into
PEEK, an alternating copolymer, 6, was prepared by reacting equal
amounts of 1 with 4 at 185 ꢀC for 15 h. The resulting polymer was
soluble in chloroform, THF, and NMP, which allowed the polymer to
be fully characterized (see Table 1). The Mw was determined to be
62,500 Da with a polydispersity index of 4.8. The 13C NMR spectrum
(Fig. 2b) confirmed the presence of all of the expected signals from
both the PEEK and m-PEEK components. Thermal analysis of this
sample also indicated a completely amorphous material with only
a Tg, 127 ꢀC, being observed in heating ramps up to 400 ꢀC (Fig. 3).
In an effort to enhance the potential for crystallization, a series
of copolymers, in which progressively decreasing levels of m-PEEK
segments were introduced, was prepared as outlined in Scheme 3.
For discussion purposes the copolymers will be labeled Pxx-co-m-
Pxx where xx is the mol% of each type of repeat unit while P and m-P
represent PEEK and m-PEEK, respectively. The synthesis of a more
PEEK-like structure required the synthesis of an alternative
bisphenol, 4,40-bis-(4-hydroxyphenoxy)benzophenone, 3, which
was prepared according to the procedure reported by Hwang et al.
[23] As shown in Scheme 3, reaction of equimolar amounts of 2
with 3, to form 7a, provided the same alternating (P50-alt-m-P50
)
material prepared via the pendant bisphenol route (1 þ 4, Scheme
2), 6, which was confirmed by NMR spectroscopy (Fig. 2c). Because
it contains one “built in” PEEK repeat unit, in addition to the
requisite hydroquinone, this alternative bisphenol afforded the
opportunity to prepare more “PEEK-like” copolymers.
Table 1
Formulations and molecular weight data for polymers 5, 6, and 7aee. All reactions
were performed in NMP at a temperature of 185 ꢀC.
Polymer Bisphenol
1
2
Molar 1st
2nd
% Yield Mw (Da) PDI
ratio
step (h) step (h)
5
6
4
4
3
3
3
3
3
0
1
0
1
0
1
0:100 48
50:50 15
50:50 24
e
e
e
8
8
8
42%
45%
62%
71%
75%
49%
77%
15,600 3.1
62,500 4.8
45,600 2.6
7a
7b
7c
7d
7e
0.5 0.5 75:25 16
0.6 0.4 80:20 16
0.7 0.3 85:15 16
0.8 0.2 90:10 16
e
e
e
e
e
e
e
e
8
Fig. 3. DSC traces (2nd heat) of m-PEEK, 5, and the alternating copolymers 6 and 7a.

A. Fortney, E. Fossum / Polymer 53 (2012) 2327e2333
2331
Table 2
however, it was soluble in room temperature DMAc, and NMP, but
required heating in DMSO. As expected, the higher percentages of
PEEK segments lead to diminished solubility properties. For
example, the P85-co-m-P15 sample was only soluble in hot NMP
while the P90-co-m-P10 was insoluble, even in hot NMP. Unfortu-
nately, the limited solubility prevented the determination of Mw
values for all of the samples with PEEK contents above 50%.
Solubility characteristics of polymers 5, 6, and 7aee. Solubility tests were performed
with 3 mg samples in 1 mL of the solvent.
Solvent
5
6
7a
7b
7c
7d
7e
CHCl3
THF
DMF
DMSO
DMAC
NMP
þ
þ
þ
þ
þ
þ
e
þ
þ
þ
þ
þ
þ
e
þ
þ
þ
þ
þ
þ
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
þ/ꢂ
þ
e
e
e
e
þ
þ/ꢂ
e
þ/ꢂ
e
3.2. Thermal properties
Toluene
e
þ ¼ soluble at room temperature.
þ/ꢂ soluble when heated.
e ¼ insoluble.
The thermal properties of m-PEEK, 5, and the copolymers, 6,
7aee, were evaluated via thermogravimetric analysis (TGA) and
differential scanning calorimetry (DSC) and the data is summarized
in Table 3. All of the samples possessed relatively good thermal
stability, both under nitrogen and air atmospheres. The 5% weight
loss temperatures, Td-5%, values under nitrogen increased from
480 ꢀC for 7a to 531 ꢀC for 7e, showing a steady rise as the
percentage of PEEK segments increased. Similar trends were
observed in the TGA data acquired in air.
The DSC cooling curves and the second heating traces for 7aee
are shown in Fig. 4a and b, respectively. In the cooling curves all of
the polymers displayed a glass transition temperature, Tg, however,
two of the samples, 7d and 7e, also displayed a crystallization
temperature, Tc, indicating that they were semi-crystalline mate-
rials. Since these two samples had 85 and 90% of PEEK segments,
the observation of crystallization was not unexpected. The
observed Tg values showed a significant increase as the ratio of
PEEK to m-PEEK was increased. For example, the Tg of P50-alt-m-P50
(7a) was 128 ꢀC, while that of P85-co-m-P15 (7d) increased to 148 ꢀC.
The increased values of Tg at higher levels of PEEK can be attributed
to both the change in backbone structure and the presence of some
crystallinity.
Subsequently, a series of Pxx-co-m-Pxx materials, with ratios of
75:25, 80:20, 85:15, and 90:10, were prepared by first reacting 3
with varying molar ratios of 2 (See Table 1) for 16 h at 185 ꢀC,
followed by the addition of the appropriate quantity of 4,40-
difluorobenzophenone, 1, (Scheme 3) and continuing the reaction
for 8 additional hours. At higher percentages of PEEK segments
there were immediate differences in the solution viscosity and
solubility characteristics. For example, the viscosity of the reaction
mixture was visually much higher for the P80-co-m-P20 sample, 7c,
than the P50-alt-m-P50 sample, 7a, after the same 24-h reaction
time. The final yield of polymer generally increased as the m-PEEK
component decreased. In part, this observation can be attributed to
the removal of cyclic oligomers during the reprecipitation process.
When more of the monomer 2 is present in the reaction mixture,
the formation of cyclic material is highly likely as shown in previous
examples with 3,5-difluoro aromatic systems [20e22].
The solubility characteristics of the series are summarized in
Table 2 and it is readily apparent that the more PEEK-like structures
possessed considerably lower solubility in all of the solvents tested.
While the P50-alt-m-P50 sample was soluble in THF, chloroform,
etc., the P75-co-m-P25, was insoluble in THF and chloroform,
The Tg’s observed for 7aee, in the second heating traces,
essentially mirrored those from the cooling curves, however, the
transition was less intense at higher ratios of PEEK to m-PEEK. The
Table 3
Thermal analysis data for polymers 5, 6, and 7aee.
Polymer
TGAa
DSC cooling
curveb
DSC 2nd heating curvec
N
2 Td-5%
Air Td-5%
(ꢀC)
Tg
(ꢀC)
Tc
(ꢀC)
D
(J/g)
H
Tg (ꢀC)
Tc
(ꢀC)
D
(J/g)
H
Tm
(ꢀC)
DH
(J/g)
(ꢀC)
5
6
428
530
480
508
519
529
531
426
519
467
476
511
517
522
104
124
128
136
140
148
154
e
e
105
127
126
137
138
143
147
e
e
e
e
e
e
e
e
e
e
7a
7b
7c
7d
7e
e
e
e
e
e
e
e
e
e
e
e
e
e
e
216
e
8.6
e
284
307
316
10.3
19.1
27.2
226
254
25.9
33.4
e
e
a
Heating rate of 20 ꢀC/min.
Cooling rate of 10 ꢀC/min.
Heating rate of 10 ꢀC/min.
b
c
Scheme 3. Synthesis of Pm-co-meta-Pn Copolymers, 7aee.

2332
A. Fortney, E. Fossum / Polymer 53 (2012) 2327e2333
Fig. 5. X-ray diffraction patterns of (a) polymer 6, (b) 7a, (c) 7b, (d) 7c, (e) 7d, and (f)
7e.
4. Conclusions
PEEK analogs (m-PEEK), based on 3,5-difluorobenzophenone, 2,
were prepared by polycondensation reactions with two oligomeric
bisphenols, 4,40-bis(4-hydroxyphenoxy)benzophenone, 3, and 3,5-
bis(4-hydroxyphenoxy)benzophenone, 4. In both cases, completely
amorphous polymers resulted, even with the “built in” PEEK
segments found in 3. The glass transition temperatures of these two
polymers were 127 and 105 ꢀC, respectively. Semi-crystalline PEEK
analogs were prepared using 3 and varying ratios of 4,40-difluor-
obenzophenone, 1, and 2. The samples with 80 mol% or higher of
PEEK segments possessed some degree of crystallinity, as deter-
mined by DSC and X-ray diffraction, but were also soluble, to
a limited extent in organic solvents such as NMP. The glass transi-
tion temperatures, Tg, of the copolymers increased from 126 to
147 ꢀC as the percentage of PEEK was increased from 50 to 90 mol%.
The melting temperatures, Tm, also showed a similar trend with the
80:20 and 90:10 samples displaying Tm values of 284 and 316 ꢀC,
respectively. In addition, the use of monomer 2 affords PEEK
systems that carry pendant benzoyl groups, which provide versatile
sites for the introduction of functional groups and exploration of
this particular aspect is ongoing.
Fig. 4. DSC traces of copolymers 7aee under nitrogen: (a) first cooling curves and (b)
second heating curves.
P80-co-m-P20 (7c) sample displayed both a Tc (216 ꢀC) and melting
temperature, Tm, (284 ꢀC) indicating that it possessed the ability to
crystallize. Both the P85-co-m-P15 (7d) and P90-co-m-P10 (7e)
samples displayed very weak Tg’s, but quite visible Tm’s. The
enthalpy for the Tm increased substantially on going from 7c to 7d
to 7e (10.3, 19.1, and 27.2 J/g) and the Tm also shifted to higher
values, 284, 307, and 316 ꢀC, respectively. While the observed Tm
values are significantly lower than that of PEEK itself, which has
a Tm of 343 ꢀC, the materials, with the exception of 7e, also dis-
played significantly better solubility characteristics.
3.3. Crystallinity via X-ray diffraction
Confirmation of the semi-crystallinity present in 7cee was
provided through powder X-ray diffraction studies as depicted in
Fig. 5. Polymer 7e exhibited the most noticeable diffractions,
located at w19, 21, 23, and 29ꢀ, which are quite similar to the (110),
(111), (200), and (211) reflections that are the reported values for
PEEK [17,24]. As the percentage of PEEK segments decreased, the
distinct signals broadened and eventually disappeared into the
amorphous halo (samples 6 and 7a), which is consistent with the
observations from the DSC analysis. Interestingly, the diffraction
pattern for 7b seems to indicate the presence of a very low level of
crystallinity, which was not readily observed in the corresponding
DSC traces.
Acknowledgments
This material is based upon work supported by the National
Science Foundation under CHE-1012392. Professor David Grossie of
Wright State University is acknowledged for his assistance in
obtaining the X-ray diffraction data.

A. Fortney, E. Fossum / Polymer 53 (2012) 2327e2333
2333
[13] Carlier V, Devaux J, Legras R, Bunn A, McGrail PT. Polymer 1994;35(2):
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