Poly(imino ketone)s as new high-performance polymers

Article abstract of DOI:10.1021/ma0490101

A series of novel poly(imino ketone)s (PIK) have been synthesized via palladium-catalyzed polycondensation (Hartwig-Buchwald reaction) of aromatic dichloro or dibromo ketones with various aromatic diamines. The influence of the halogen-containing monomers

Full text of DOI:10.1021/ma0490101

Macromolecules 2004, 37, 8269-8277
8269
Poly(imino ketone)s as New High-Performance Polymers
Aym a n S. Al-Hu ssa in i, Ma r k u s Kla p p er , Ta d eu sz P a k u la , a n d Kla u s Mu1 llen *
Max Planck Institute for Polymer Research, Ackermannweg 10, D-55128 Mainz, Germany
Received May 19, 2004; Revised Manuscript Received August 8, 2004
ABSTRACT: A series of novel poly(imino ketone)s (PIK) have been synthesized via palladium-catalyzed
polycondensation (Hartwig-Buchwald reaction) of aromatic dichloro or dibromo ketones with various
aromatic diamines. The influence of the halogen-containing monomers, concentration, temperature, and
catalyst ligands on the polycondensation reaction and on the polymer polydispersity was investigated.
These polymers showed good thermal stability with high decomposition temperatures. FT-IR spectra of
the PIKs revealed that in the solid state intermolecular and intramolecular hydrogen bonding
(N-H‚‚‚OdC) are present. A model compound was synthesized and characterized by standard spectroscopic
methods in order to assist in the structure proof of the polymer. The mechanical behavior of the PIK
polymers suggests that they can be considered as a new class of high-performance polymers.
In tr od u ction
In the 1980s high-performance polymers were con-
sidered the most promising class of polymers for special
applications in automotive, aircraft, and spacecraft
industry or medicine1 due to their outstanding physical
properties.2-9 However, because of their high production
costs, only a few types have been commercialized. One
example is semicrystalline poly(arylene ether ketone)s
(PEKs).3-9 Much research effort has been dedicated to
the structural variation of PEKs to control and improve
their properties.2 Poly(arylene ether ketone)s can be
prepared via a polycondensation using electrophilic or
nucleophilic aromatic substitution.3-6 In the latter case
fluoride has been employed as a leaving group. The nitro
group has rarely been used because of the generation
of nitrite ions that become reactive and cause side
reactions at elevated temperatures.10a-e
Another example of aromatic polymers are poly-
(arylene amide)s (PAAs). They are materials with high
thermal stability, good chemical resistance, and high
tensile properties.11,12 However, their high glass transi-
tion temperatures (Tg) and insolubility in organic sol-
vents seriously limit their processability.13,14
F igu r e 1. PIK as hybrid material of PEK, PANI, and PAA.
A third type of aromatic polymers is polyaniline
(PANI). It was not used as a high-performance polymer
but as a conducting material.15 It has attracted consid-
erable attention due to its simple synthesis, good
environmental stability, and high electrical conductivity.
Polyaniline can be synthesized by both electrochemical
and chemical oxidative polymerization.16 Recent work
has shown that polyaniline prepared at room temper-
ature is of fairly low molecular weight17 and contains
defect sites.18 Considerable effort has been made to
develop relationships between synthetic conditions and
properties of polyaniline obtained by electrochemical
polymerization.19 By contrast, little attention has been
paid to the chemical polymerization.20-22
In this paper, we report the synthesis of aromatic
poly(imino ketone)s (PIKs) using the Hartwig-Buch-
wald reaction.23a-o These polymers are promising can-
didates as high-performance polymers and can be
considered as a hybrid structure of poly(arylene ether
ketone)s (PEKs), polyaramides (PAAs), and polyaniline
(PANI) (Figure 1). The catalytic amination reaction of
arylene halides with primary amines using palladium
complexes has become an important synthetic procedure
for a variety of arylene amines including pharmaceu-
ticals, electronic materials, and ligands for metal cata-
lysts. The Pd-catalyzed aryl amination has also been
applied to polycondensation reactions to give various
polyamines and its related poly(iminoarylene)s with no
or scarcely cross-linked structures.24a-c Herein our aim
is to use this method for synthesizing poly(imino
ketone)s (PIKs) as a new polymer structure. We ex-
pected the polycondensation of different aromatic diha-
lides with primary aromatic diamines using the catalytic
system generated from tris(dibenzylideneacetone)di-
palladium(0) Pd2(dba)3 and 2,2′-bis(diphenylphosphino)-
1,1′-binaphthyl (BINAP) (Figure 3) to produce soluble
poly(imino ketone)s (PIKs). The use of inexpensive
monomers with bromine or chlorine leaving groups
instead of expensive fluorine containing monomers is,
as has already been shown for PEEKKs (poly(ether
ether ketone ketone)s), very attractive for obtaining
aromatic polymers.9 We expect that the amino and
carbonyl groups in PIKs would result in intermolecular
10.1021/ma0490101 CCC: $27.50 © 2004 American Chemical Society
Published on Web 10/01/2004

8270 Al-Hussaini et al.
Macromolecules, Vol. 37, No. 22, 2004
F igu r e 2. 1H NMR (700 MHz) spectrum of polymer 13 recorded in DMSO-d6 at 100 °C.
F igu r e 3. Complex ligands of the catalyst applied in the Buchwald-Hartwig reaction (1: BINAP; 2: di-tert-butylphosphinobi-
phenyl; 3: P(tBu)3; 4: 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride).
Elmer model 2400 CHN analyzer. 1H NMR and 13C NMR
hydrogen bonds like in KEVLAR, leading to good
spectra were recorded using Bruker AMX250 Hz, Bruker
AC300 Hz, and Bruker AMX700 Hz NMR spectrometers in
CDCl3, CD2Cl2, or DMSO-d6, depending on the solubility of
the material being analyzed. Mass spectra were measured on
a Fisons Trio 2000 under electron impact or field desorption
conditions. Intrinsic viscosity was measured at 25 °C in DMF
or in THF, using a Cannon-Ubbelohde viscometer. The intrin-
sic viscosity value [η] was obtained by measuring specific
viscosity ηsp ) η/η0 - 1 and reduced viscosity ηred ) ln(η/η0) at
four different concentrations, plotting ηsp/c vs c and extrapolat-
ing to zero concentration. DSC was performed on either a DSC
I Mettler TC 10 A or a DSC II Mettler TC 11. The DSC curves
obtained during the second heating scan were taken into
consideration. The samples were heated at a rate of 10 °C/
min under flowing nitrogen gas. Tg values were identified as
the midpoint of the change in endothermic baseline from the
second heating after a quench cooling from the first run.
Thermogravimetric analysis (TGA) was performed on a Mettler
TC 10A at a heating rate of 10 °C/min under air and nitrogen
thermal and mechanical properties that are essential
requirements for high-performance polymers.25
Exp er im en ta l Section
Ma ter ia ls. 1,4-Bis(4-chlorobenzoyl)benzene (5), 1,4-bis(4-
fluorobenzoyl)benzene (6), and 5-(tert-butyl)isophthaloyldi-
chloride (8) were synthesized according to literature pro-
cedures.26-28 1,4-Bis(4-bromobenzoyl)benzene (7) was synthe-
sized according to a modified literature procedure29 (see below),
and 1,3-bis(4-bromobenzoyl-5-tert-butyl)benzene (9) was syn-
thesized as shown in Scheme 1. Other materials and reagents
were obtained from different commercial sources and used
without further purification.
Mea su r em en ts. Melting points of purified compounds were
determined on a Bu¨chi melting point apparatus at a heating
rate of no greater than 1 °C/min and are uncorrected. FTIR
spectra were recorded on a Nicolet 320 FTIR spectrometer.
UV-vis absorption spectra were recorded on a Perkin-Elmer
Lambda 15. Elemental analyses were performed on a Perkin-

Macromolecules, Vol. 37, No. 22, 2004
Poly(imino ketone)s 8271
Sch em e 1. Syn th esis of
Sch em e 2. Syn th esis of Mod el Com p ou n d 10
1,3-Bis(4-br om oben zoyl-5-ter t-bu tyl)ben zen e (9)
Schlenk flask was evacuated and backfilled with argon. The
flask was charged with Pd2(dba)3 (18.3 mg, 0.02 mmol, 2 mol
%), BINAP (37.4 mg, 0.06 mmol, 6 mol %), and NaO-t-Bu (538
mg, 5.6 mmol). The flask was evacuated, backfilled with argon,
and then capped with a rubber septum. DMAc (5 mL), 1,4-
bis(4-bromobenzoyl)benzene (888 mg, 2.0 mmol), aniline (373
mg, 4 mmol), and additional DMAc (2 mL) were added through
the septum. The flask was fitted with a reflux condenser, and
the mixture was heated to 160 °C with stirring for 24 h. The
resulting solution was allowed to slowly cool to room temper-
ature and subsequently poured into cold water, filtered
through Celite, and dried. The crude material was purified
by flash chromatography on silica gel and recrystallized from
toluene to afford 10 as yellow crystals. Yield: 825 mg, 88%;
atmosphere. GPC measurements were used to determine
molecular weights and molecular weight distributions by
universal calibration generated with narrow molecular weight
distribution polystyrene standards using tetrahydrofuran or
dimethylformamide as eluent.
Syn th esis. Syn th esis of 1,4-Bis(4-br om oben zoyl)ben -
zen e (7) (Mod ified P r oced u r e).28 40 g of anhydrous pow-
dered aluminum chloride (0.3 mol) was added to a stirred
solution of 25.4 g of terephthaloyl chloride (0.125 mol) and
255.14 g of bromobenzene (1.63 mol). After an exothermic
reaction which raised the temperature to 30 °C, the solution
was stirred at room temperature for 12 h and then heated at
95 °C for 2 h. After cooling, the solution was poured into cold
aqueous hydrochloric acid to precipitate a solid which was
isolated by filtration. The cream-colored solid was thoroughly
washed with water, sodium bicarbonate solution (10%), and
water and then dried at 100 °C in air. The crude product was
recrystallized from N,N-dimethylacetamide (DMAc) or toluene
to give 7 as colorless crystals. Yield: 52.2 g, 94%; mp 274-
1
mp 248-50 °C. H NMR (250 MHz, DMSO-d6, rt): δ ) 8.77-
(S, NH); 7.56 (s, 4H, H6); 7.50 (d, 4H, H5); 7.13 (t, 4H, H4);
7.03 (d, 4H, H3); 6.93 (d, 4H, H2), 6.80 (t, 2H, H1). 13C NMR
(62.5 MHz, DMSO-d6, rt): δ ) 193.1 (C3), 148.8 (C7), 140.8
(C8), 132.5 (C2), 129.4 (C5), 128.8 (C1), 126.3 (C10), 122.3 (C4),
119.8 (C11), 119.7 (C9), 113.7 (C6). MS (m/z): 468.9 (molecular
peak), 467.9, 422.6, 300.3, 285.3, 238.9, 195.8 (100%), 166.7,
151.0; FTIR (KBr pellet): γNH at 3341 cm-1; γCdO at 1633
cm-1, γC-H aromatic at 3049 cm-1 and C-N at 1338 cm-1
;
UV recorded in DMF λmax at 296.7 and 374.1 nm. Anal. Calcd
for C32H24N2O2 (468.55): C, 82.03; H, 5.16; N, 5.98. Found:
C, 81.54; H, 4.93; N, 5.20.
1
275 °C. H NMR (300 MHz, DMSO-d6, 100 °C): δ ) 7.86 (s,
4H, H3), 7.76 (d, 4H, H2, m to Br), 7.73 (d, 4H, H1, O to Br).
MS (EI): 444.10. Anal. Calcd for C20H12Br2O2 (444.12): C,
54.09; H, 2.72; Br, 35.98. Found: C, 54.00; H, 2.70; Br, 35.56.
IR spectra (KBr pellet): 840, 843 cm-1 (p-disubstituted
benzene); 1640 cm-1 carbonyl group).
Syn th esis of P oly(im in o k eton e)s (Sch em e 3). Meth od
a . To a Schlenk flask equipped with magnetic stirrer, an argon
outlet, inlet, and water-cooled condenser, dibromo compound
(4 mmol), diamine (4 mmol), sodium tert-butoxide (1.076 g, 11.2
mmol), tris(dibenzylideneacetone)dipalladium(0) (36.6 mg, 0.04
mmol), BINAP (74.8 mg, 0.12 mmol), and dimethylacetamide
(6-8 mL) were added. The reaction mixture was evacuated
and flushed with high-purity argon. This procedure was
repeated five times. The flask was immersed with continuous
stirring in a 100 °C oil bath for 4 h and in a 165 °C oil bath
for 20 h. The resulting polymer solution was allowed to slowly
cool to room temperature, filtered, and subsequently poured
into cold water, filtered, washed with water and methanol,
and then dried at 100 °C under vacuum. The elemental
analyses of typical polymers 11a , 11c, and 14a are listed in
Table 2.
Syn th esis of 1,3-Bis(4-br om oben zoyl-5-ter t-bu tyl)ben -
zen e (9) (Sch em e 1). A mixture of 5-tert-butylisophthalic acid
(25 g, 0.113 mol) and SOCl2 (250 mL) was stirred at reflux for
24 h. The excess SOCl2 was distilled off under vacuum, and
the resultant acid chloride was used in the following Friedel-
Crafts benzoylation without further purification. Bromoben-
zene (230.6 g, 1.469 mol) was added to the acid chloride, and
the solution was cooled in an ice-water bath. Anhydrous
aluminum chloride (36 g, 0.27 mol) was added slowly such that
the temperature did not exceed 5 °C. The obtained red
suspension was stirred at room temperature for 16 h and then
at 60 °C for 4 h. The reaction mixture was allowed to cool to
room temperature and poured into a mixture containing ice-
water and concentrated HCl. The pale yellow precipitate was
washed with water and sodium bicarbonate solution (10%),
resulting in a colorless solid which was dried in an oven. Two
recrystallizations from chloroform/petroleum ether gave 9 as
colorless crystals. Yield: 49.8 g, 88.2%; mp 167-68 °C. 1H
NMR (250 MHz, CD2Cl2, rt): δ ) 8.01 (s, 2H, m to t-Bu group),
7.84 (1H, p to t-Bu group), 7.65 (dd, 4H), 7.49 (d, 4H), 1.36 (s,
9H, t-Bu group). 13C NMR (62.5 MHz, CD2Cl2, rt): δ ) 195.2,
152.7, 137.6, 136.4, 132.9, 132.1, 131.0, 128.1, 126.4, 35.4, 31.2.
MS(m/z): 499.60 (molecular peak). Anal. Calcd for C24H20Br2O2
(500.23): C, 57.63; H, 4.03; Br, 31.95. Found: C, 57.04; H, 3.89;
Br, 31.62.
Meth od b. To a Schlenk flask equipped with magnetic
stirrer, an argon outlet, inlet, and water-cooled condenser,
dibromo compound (4 mmol), diamine (4 mmol), sodium tert-
butoxide (1.076 g, 11.2 mmol), tris(dibenzylideneacetone)-
dipalladium(0) (36.6 mg, 0.04 mmol), BINAP (74.8 mg, 0.12
mmol), lithium chloride (0.96-1.4 g), and diphenyl sulfone (7-
10 g) were added. The reaction mixture was evacuated and
flushed with high-purity argon. This procedure was repeated
five times. The flask was immersed with continuous stirring
in a 165 °C oil bath for 4 h and in a 200 °C oil bath for 20 h.
The reaction mixture was then cooled to room temperature.
The obtained powder was subsequently washed with acetone
to remove the solvent and dissolved in dimethylformamide,
filtered, precipitated by acetone to ensure removal of salts,
washed with water many times, and then dried at 100 °C
Syn th esis of 4,4′-Bis(4-a n ilin oben zoyl)ben zen e (10) a s
a Mod el Com p ou n d (Sch em e 2). An oven-dried resealable

8272 Al-Hussaini et al.
Macromolecules, Vol. 37, No. 22, 2004
Sch em e 3. Syn th esis of P oly(im in o k eton e)s (P IKs)
under vacuum. The elemental analyses of typical polymers
11b, 12a , 13, 14b, 15, and 16a are listed in Table 2.
to a palladium(0) species to form an arylene palladium-
(ΙΙ) halide. By inductive effect or by resonance, this step
should be favored for an arylene bromide substituted
with an electron-withdrawing group in the ortho or para
position. To investigate the potential of the amination
reaction for a polycondensation process, 4,4′-bis(4-anili-
Resu lts a n d Discu ssion
The accepted mechanism of the Pd-catalyzed amina-
tion involves oxidative addition of the aromatic halides

Macromolecules, Vol. 37, No. 22, 2004
Poly(imino ketone)s 8273
Ta ble 1. Ch a r a cter iza tion of P IKs (GP C, In tr in sic Viscosity, F TIR, a n d Yield )
a
a
b
polymer code
Mh n
Mh w
Mh w/Mh n
DPc
yield (%)
γNHd
γCdOd
γC-Nd
[η],e g/dL
11a
11b
11c
12a
13
14a
14b
15
f
25
23
24
18
f
82
49
126
95
89.9
92
80
88
86
88
84
90
3318
3322
3320
3377
3360
3348
3384
3422
3364
1631
1635
1638
1642
1644
1646
1644
1663
1646
1312
1314
1316
1308
1307
1310
1327
1330
1328
f
12 200
11 100
15 000
11 700
25 300
74 100
26 300
19 500
2.1
6.7
1.8
1.7
0.18
0.16
0.19
0.17g
f
0.42
0.249
0.685
44 200
37 000
85 900
295 200
139 300
474 500
6.7
3.8
5.5
16a
a
b
By GPC (calibrated by polystyrene standards). Polydispersity index. c Degree of polymerization determined from number-average
molecular weight. FTIR (KBr, pellet). e [η] ) intrinsic viscosity measured at 25 °C in DMF. f Not measured due to poor solubility.
Measured at 25 °C in THF.
d
g
Ta ble 2. Elem en ta l An a lysis for P oly(im in o k eton e)s
elemental analysisa (%)
polymer code
formula (mol wt %)c
C
H
N
moisture uptakeb
3.60
11a
(C26H18N2O2)n
(390.4411)n
calcd
found
corrected
calcd
found
corrected
calcd
found
corrected
calcd
found
corrected
calcd
found
corrected
calcd
found
corrected
calcd
found
corrected
calcd
found
79.98
76.70
79.46
79.65
77.52
79.55
79.65
76.80
79.59
84.31
83.10
84.28
84.31
82.62
84.19
80.69
74.83
79.96
80.27
74.60
79.80
81.79
77.69
81.52
84.42
79.81
84.36
4.65
4.86
4.69
4.60
4.73
4.61
4.60
4.78
4.61
6.11
6.19
6.10
6.11
6.21
6.08
5.87
6.23
5.80
5.61
6.08
5.66
5.92
5.99
5.69
6.79
7.18
6.77
7.17
6.89
7.14
5.81
5.67
5.82
5.81
5.80
6.01
4.47
4.33
4.39
4.47
4.34
4.43
6.27
5.86
6.26
5.20
4.85
5.19
3.74
3.68
3.50
4.10
3.81
4.03
11b
11c
12a
13
(C32H22N2O3)n
(482.5383)n
2.62
3.63
1.42
2.03
6.85
6.97
4.93
5.70
(C32H22N2O3)n
(482.5383)n
(C44H38N2O2)n
(626.7979)n
(C44H38N2O2)n
(626.7979)n
14a
14b
15
(C30H26N2O2)n
(446.5486)n
(C36H30N2O3)n
(538.6458)n
(C51H44N2O4)n
(748.9214)n
corrected
calcd
16a °
(C48H46N2O2)n
(682.9054)n
a
For C and N corrected value ) found value × (100% + moisture uptake %). For H corrected value ) found value × (100% - moisture
b
uptake %). Moisture uptake (%) ) (W - W0)/W0 × 100%. W is the weight of polymer sample after standing at room temperature; W0 is
the weight of polymer sample after drying in a vacuum at 100 °C for 10 h. c In g mol-1
.
nobenzoyl)benzene (10) was synthesized as a model
compound by a palladium-catalyzed amination of 1,4-
bis(4-bromobenzoyl)benzene (7) with aniline as a pri-
mary aromatic amine using NaO-t-Bu as a base and
BINAP (1) (Figure 3) as a ligand.
DMAc was used as a solvent at a temperature of 100
°C for 4 h followed by 165 °C for 20 h. In method (b)
diphenyl sulfone (DPS) was applied as a solvent at a
temperature of 165 °C for 4 h and then 200 °C for 20 h,
and lithium chloride was added to hinder intermolecular
and intramolecular hydrogen bonding of the PIK prod-
ucts and to thus increase the solubility. The relative
amounts of monomers and DPS were adjusted to
maintain a solid content of 30-36% during the poly-
condensation process. The reactions of the dibromo
monomers 7 and 9 with the arylene diamines having
electron-donating substituents provided the correspond-
ing PIKs in 80-95% yields without undesired side
products (work-up method a or b).
The isolated yield was 88% after column chromatog-
raphy, while there were no minor undesired products
1
detected by H and 13C NMR spectroscopy, (FD+) mass
spectra, or thin-layer chromatography.
P olym er Syn th esis. Reactions of electron-poor aro-
matic halides and electron-rich amines give the highest
yields in the amination protocol.30 Thus, we attempted
polycondensation of 1,4-bis(4-bromobenzoyl)benzene (7)
and 1,3-bis(4-bromobenzoyl-5-tert-butyl)benzene (9) as
electron-poor arylene bromides with a series of electron-
rich primary aromatic diamines. The results of the Pd-
catalyzed polycondensation of these aromatic bromides
with different aromatic diamines are listed in Table 1.
Two methods were developed for the synthesis of poly-
(imino ketone)s (Scheme 3).
The polymer solubility depended on the nature of the
solvent, the molecular weight, and chemical structure
of the polymer. Polymers 11b, 11c, 12a , 13, 14b, 15,
and 16a could be dissolved in aprotic solvents such as
NMP, DMAc, DMSO, and DMF while only swelling was
observed in other common organic solvents such as
chloroform and dichloromethane. The complete dissolu-
tion process took from a few minutes (polymer 11b in
In both methods the combination of Pd2(dba)3 and
BINAP was used as an efficient catalyst. In method a,

8274 Al-Hussaini et al.
Macromolecules, Vol. 37, No. 22, 2004
Ta ble 3. Differ en t Exp er im en ta l Con d ition s for th e P olycon d en sa tion of 2,2-Bis[4-(4-a m in op h en oxy)p h en yl]p r op a n e w ith
1,3-Bis(4-br om oben zoyl-5-ter t-bu tyl)ben zen e To F or m P olym er 15
run
temp (°C)
concn of monomers (%)
solubility
yield (%)
Mh w
Mh n
Mh w/Mh n
DP
1
2
3
4
5
6
100
100
165
165
165
100-165
18
36
24
30
36
36
DMF, DMAc, THF
DMF, DMAc, THF
DMF, DMAc, THF
swelling in DMF, DMAc, THF
swelling in DMF, DMAc, THF
DMF, DMAc, THF
92
90
98
95
96
96
4000
10000
11000
1000
2000
7000
4
5
1.6
1.3
2.6
9
42000
10000
4.2
13
Ta ble 4. P d -Ca ta lyzed P olycon d en sa tion of
DMF) up to several hours (polymer 16a in DMF about
24 h).31
1,3-Bis(4-br om oben zoyl-5-ter t-bu tyl)ben zen e (9) w ith
4,4′-(1,4-P h en ylen ed iisop r op ylid in e)bisa n ilin e Usin g
Differ en t Liga n d sa
The molecular weights of the reprecipitated polymers
were measured by GPC (calibrated by polystyrene
standards). The Mn values are in the range of 11 100-
85 900 and the Mw values in the range of 19 500-
474 500. The polydispersities vary from 1.7 up to 6.7
(Table 1). Especially, with increasing molecular weights
the polydispersity increases drastically.32
The elemental analysis of the polymers showed that
in all cases the determined carbon and nitrogen content
were lower than the calculated ones. This can be
explained by the hygroscopic nature of the imino groups
of these polymers. The uptake of water was in the range
of 1.4-7.0% as calculated from the weight change of the
vacuum-dried polymer samples after exposure to air at
room temperature for 10-12 h. Therefore, the measured
elemental analysis values were corrected by elimination
of the amount of absorbed water (Table 2). Similar to
the study performed on hygroscopic polyaramides,33 the
experimental data were then in good agreement with
the calculated ones.
polymer
code
yieldc
(%)
d
d
g
run
ligandb
Mn
Mw
DPf Mw/Mn
1
2
3
16a
16b
16c
16d
1
2
3
4
90
85 900 474 500 126
5.5
5.1
8.5
9.6
80.9 28 000 142 000
41
7
78
73
0
5 000
5 000
59 000
52 000
4
7
5e
a
The polycondensation of electron-poor 1,3-bis(4-bromobenzoyl-
5-tert-butyl)benzene (4 mmol) was carried out in the presence of
Pd2 (dba)3 (0.12 mmol), ligand (P/Pd ratio ) 3/1), and NaO-t-Bu
(11.2 mmol) in diphenyl sulfone at 165 °C for 4 h and at 200 °C
b
for 24 h. 1 ) BINAP; 2 ) di-tert-butylphosphinobiphenyl; 3 )
P(tBu)3; 4 ) 1,3-bis(2,6-diisopropylphenyl)imidazolium chloride.
d
c Reprecipitated polymer. Calibrated by GPC (DMF) polystyrene
standards. e No catalyst was added. f Degree of polymerization
determined from number-average molecular weight. g Polydisper-
sity index.
are not detectable, but they cannot be excluded as they
are expected in the same region as the resonances of
the proton H1. As the concentration of end groups in
polymer 13 is very low, the corresponding 13C NMR
signals were not detectable.
The end groups were only detected in the case of
polymer 13, as shown from the 1H NMR spectrum.
Remarkably, no end groups were detected in the case
of the higher molecular weight PIKs.
During the synthesis of polymer 15, the effect of
concentration and temperature on the molecular weight
could be followed. Upon increasing the temperature
from 100 to 165 °C and the concentration from 18% to
24%, Mw increased from 4000 to 10 000 and Mn from
1000 to 7000, while upon increasing the concentration
form 24% to 36% at temperature 165 °C, Mw increased
from 11 000 to 42 000 and Mn from 7000 to 10 000. A
temperature of 165 °C and a concentration of 36% are
more suitable for the palladium-catalyzed polyconden-
sation to produce polymer 15 with higher molecular
weight (Table 3).
To test which ligand would be most suitable for the
polycondensation process to form PIKs, we attempted
the amination of 1,3-bis(4-bromobenzoyl-5-tert-butyl)-
benzene (9) with 4,4′-(1,4-phenylenediisopropylidine)-
bisaniline in diphenyl sulfone using different ligands
from 1 to 4 (Figure 3, Table 4).
It appears that ligand 1 gives better yields, higher
molecular weight, and lower polydispersity of the poly-
mer than ligand 2 and that both are superior to 3 and
4.
The reactivity of the halogen-containing monomers
(5-7) was studied during the polycondensation process
to form polymer 12a (Table 5). The use of 1,4-bis(4-
bromobenzoyl)benzene (7) gave polymer 12a in better
yield higher molecular weight than 1,4-bis(4-chloroben-
zoyl)benzene (5) while 1,4-bis(4-fluorobenzoyl)benzene
(6) is totally unreactive. It is known that for aryl
In ter m olecu la r a n d In tr a m olecu la r Hyd r ogen
Bon d in g. Hydrogen-bonding interactions of polymers
have frequently been studied by FTIR spectroscopy.34,35
Therefore, IR spectra of all PIKs (KBr pellets) were
recorded, giving results in good agreement with the
proposed structure. The characteristic absorptions for
carbonyl groups γ(CdO) appeared between 1631 and
1663 cm-1 and for aromatic amino groups γ(NH) be-
tween 3318 and 3422 cm-1 (Table 1). Obviously, because
of hydrogen bonding, a significant broadening and
lowering of the absorption frequency of the bands
(γ(CdO), γ(NH)) are observed.36 This effect is known
to be a function of the degree and strength of the
hydrogen bonding.37,38 This clearly indicates that N-H‚
‚‚OdC interactions within the same molecule (intramo-
lecular hydrogen bonding) or from neighboring mol-
ecules. Intermolecular hydrogen bonding is very likely
as the solubility of all polymers is limited but can be
drastically improved by the addition of lithium chloride
known to break hydrogen bonds.7 This confirms our
assumption that these polymers may be considered as
analogous materials to polyaramides. Comparing the
frequencies of the N-H bond of the crystalline model
compound 10 (3341 cm-1) with those observed in the
polymers (12a , 13, 14a , 14b, 15, and 16a : 3377, 3360,
3348, 3384, 3422, and 3364 cm-1), a shift to higher
frequencies is observed. This suggests that the hydrogen
bonding in PIKs is weaker than in the crystalline model
compound.
1H NMR (700 MHz) spectra of all the soluble polymers
were recorded. As an example, the spectra of 13 are
1
shown in Figure 2 (DMSO-d6 at 100 °C). From the H
NMR spectra we can conclude that polymer 13 contains
a low concentration of amino end groups (resonances
at 6.4 ppm). The concentration corresponds to less than
5 mol % end groups per repeat unit. Bromine end groups

Macromolecules, Vol. 37, No. 22, 2004
Poly(imino ketone)s 8275
Ta ble 5. P d -Ca ta lyzed P olycon d en sa tion of Differ en t
1,4-Bis(4-h a loben zoyl)ben zen es w ith
4,4-(1,4-P h en ylen ed iisop r op ylid in e)bisa n ilin ea
polymer
code
c
c
d
run
R
yieldb (%)
Mn
Mw
Mw/Mn
DP
1
2
3
12a
12b
Br
Cl
F
80
76.6
0
15 000 26 300
11 000 16 000
1.8
1.5
24
17
a
The polycondensation of electron-poor 1,4-bis(4-halobenzoyl-
)benzene (4 mmol) was carried out in the presence of Pd2 (dba)3
(0.12 mmol), ligand (BINAP) (P/Pd ratio ) 3/1), and NaO-t-Bu (11.2
mmol) in diphenyl sulfone at 165 °C for 4 h and at 200 °C for 24
b
h. Reprecipitated polymer. c Calibrated by GPC (DMF) poly-
d
styrene standards. Polydispersity index.
F igu r e 5. DSC of PIKs (in N2,10 °C/min, second scan).
nitrogen. Char yield is an easy and important measure-
ment which correlates to the ability to sustain combus-
tion.39 The maximum char yield at 600 °C was obtained
for polymer 11a (83%), and the minimum was obtained
for polymer 16a (54%) in nitrogen.
By comparing for example the TGA thermograms of
12a and 13 (Figure 4), it was observed that in air a 50%
weight loss of those polymers took place at 580 and 610
°C, respectively, but in nitrogen the 50% weight loss was
not observed up to 900 °C. In air the char yield at 600
°C was 34% and 59%, but in nitrogen the char yield at
600 °C was 61% and 68%.
F igu r e 4. TGA of the polymers 12a and 13 (in N2, and in O2
10 °C/min).
Differential scanning calorimetry (DSC) of PIKs up
to 250 °C showed a single Tg, and the absence of a
melting temperature suggested an amorphous polymer
structure. A representative DSC thermogram of the
polymers is shown in Figure 5. The glass transition
temperatures of these copolymers are listed in Table 6.
All polymers show high Tgs ranging from 202 to 227 °C,
being comparable with the Tgs of modified polytereph-
thalamides bearing pendent groups connected to the
polymer backbone with ester linkages.40 Only polymer
13 gave in a lower Tg at 154 °C. The Tgs are higher than
those of the related PEKs which range from 129 to 167
°C41 and lower than those of aromatic polyamides which
amount to 292-319 °C.42 This can be explained by the
amination the reactivity decreases strongly with in-
creasing electronegativity of the halogen atoms, and
oxidative addition is rate-limiting.
Th er m a l a n d Th er m om ech a n ica l Beh a vior . All
PIKs showed high thermal stability and a high char
yield in nitrogen at 600 °C. Typical TGA traces in air
and in nitrogen are shown in Figure 4 for polymers 12a
and 13. The thermal stability was evaluated by a 5%
weight loss (Table 6). TGA curves revealed that the
polymers were thermally stable up to 323-494 °C. The
50% weight losses of the polymers took place at over
900 °C for polymers 11a , 12a , 13, 14a , and 15 in
nitrogen and for polymers 11b and 14b in both air and
Ta ble 6. Th er m a l Beh a vior of P IKs
a
b
c
d
e
polymer code
O2/N2
T5
T10
T50
W500
W600
char yield at 600 °Cf
Tg onsetg
11a
O2
N2
O2
N2
O2
N2
O2
N2
O2
N2
O2
N2
O2
N2
O2
N2
323
482
435
494
407
494
478
485
335
387
365
363
356
328
370
366
345
538
516
534
444
507
507
502
337
461
426
425
413
391
461
458
353
>900
>900
>900
582
95
6
8
6
19
7
97
17
22
22
66
39
41
32
98
29
30
32
64
40
47
46
3
83
78
78
34
61
59
68
2
71
70
68
36
60
53
54
h
11b
12a
13
212
220
154
h
>900
613
8
9
>900
344
>900
>900
>900
567
>900
715
742
14a
14b
15
94
17
21
23
26
30
22
23
215
202
227
16a
a
b
c
d
T5 ) temperature of 5% weight loss. T10 ) temperature of 10% weight loss. T50 ) temperature of 50% weight loss. W500 ) weight
loss at 500 °C, determined from TGA curve. W600 ) weight loss at 600 °C, determined from TGA curve. f The remaining of the polymer
e
at 600 °C. g From the second heating traces of DSC measurements conducted with a heating rate of 10 °C min-1 in nitrogen. Not detected
h
up to 250 °C.

8276 Al-Hussaini et al.
Macromolecules, Vol. 37, No. 22, 2004
Con clu sion s
Soluble poly(imino ketone)s with high molecular
weights have been obtained by a Pd-catalyzed polycon-
densation (Buchwald-Hartwig reaction) of aromatic
dibromides and aromatic amines. Various poly(imino
ketone)s were synthesized by using different monomers.
Four different ligands were used successfully in the Pd-
catalyzed process of which the Pd/BINAP system was
found to be the most effective catalyst; however, we do
not know whether this is due to steric or electronic
reasons. The obtained polymers may be considered as
an analogue to polyaramides since hydrogen bonding
is observed by broadening of the associated imino group
(NH) vibrational bands, while the solubility is enhanced.
On the other hand, because of the incorporated ben-
zophenone and ether moieties, one can expect similari-
ties to poly(ether ketone)s (high Young modulus, low
entanglement molecular weight).46 All these expecta-
tions are already confirmed by initial mechanical and
TGA measurements, indicating that PIKs can be con-
sidered as a new class of high-performance polymers
with a good mechanical behavior and high thermal
stability. These investigations are presently extended
and will be supported by dielectric spectroscopy. One
major advantage in comparison to the established PEKs
and polyaramides is already obvious. In comparison to
PEK, one can use cheaper monomers, e.g., chloro- or
bromo-functionalized aromatic ketones instead of the
corresponding difluoro structures. Also, the synthesis
of “activated“ intermediates as is the case for the
preparation of polyaramides by converting the aromatic
esters to e.g. acid chlorides is avoided. Furthermore,
many diamines and dibromo compounds are readily
available or easy to synthesize giving a fast access to
numerous new polymers with optimized properties such
as thermal stability, mechanical behavior, or solubility.
F igu r e 6. Mechanical behavior of polymer 15 as determined
by means of the dynamic small-amplitude shear deformation
with various deformation frequencies and at various temper-
atures. The properties are represented by frequency depend-
encies of the real (G′) and imaginary (G′′) components of the
complex shear modulus (master curves at the reference
temperature of 210 °C). The inset shows the temperature
dependence of the segmental relaxation time.
hydrogen bonding in PIKs which is weaker than that
in polyamides while PEKs have no hydrogen bonding.
The mechanical behavior of the polymers has been
examined by means of dynamic mechanical testing
performed at various temperatures and various fre-
quencies with a small-amplitude sinusoidal deforma-
tion.43 An example of the mechanical behavior deter-
mined for polymer 15 is shown in Figure 6. The results
indicate that the polymer exhibits a spectrum of vis-
coelastic properties characteristic for linear amorphous
entangled polymers. The two relaxation processes: (1)
segmental relaxation at high frequencies detected as the
cross-points of the storage (G′) and loss (G′′) modulae
on the frequency scale and (2) chain relaxation at low
frequencies (not visible) are controlling the behavior.
Refer en ces a n d Notes
These relaxations separate three states characteristic
for amorphous polymers: (1) the glassy state with the
high value of the elastic modulus (G′ ∼ 1 GPa) at high
frequencies, (2) the intermediate rubbery state with the
modulus of the order of 1 MPa (the low-frequency part
of Figure 6), and (3) the flow regime at low frequencies
with G′ , G′′ both varying with frequency in a charac-
teristic way (not visible).44 The inset in Figure 6 shows
the temperature dependence of the segmental relaxation
time which indicates that the relaxation time slows
down to nearly 100 s when the polymer is approaching
the glass transition temperature (Tg) from higher tem-
peratures. In the presented example, the rubbery pla-
teau is very well developed and extends over many
orders of magnitide of the frequency scale, indicating a
high molecular weight of polymer 15. The terminal
relaxation and the flow range are not seen in the present
data because the high Tg and the high molecular weight
of this polymer shift the detection range of such a
behavior to very high temperatures (above 250 °C).
Summarizing the first results, one can conclude that
PIKs can be considered as a new class of high-
performance polymers. They exhibit high Tgs (Tg > 140
°C) and excellent thermal stability (TD > 320 °C)
combined with good mechanical properties (storage (G′)
and loss (G′′) modulae < 108-109 and extended rubber
plateau) comparable to polyaramides or PEK.45 Fur-
thermore, because of the lack of amide bonds, these
polymers should be more stable under hydrolyzing
conditions.
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MA0490101