Specific Interactions and Miscibility of Blends of
Poly(r-caprolactam) and Sulfonated PEEK lonomer
XlNYA LUt and R. A. WEISS"
Polymer Science Program and Department of Chemical Engineering, University of Connecticut, Storrs, Connecticut
06269-31 36
SYNOPSIS
Sulfonation of poly(oxy-1,4-phenyleneoxy-1,4-phenylenecarbonyl-l,4-phenylene),
PEEK,
improves its miscibility with poly(t-caprolactam), Nylon-6 (N6).This article describes the
thermal transitions and the specific interactions that occur for blends of the free acid
derivative (H-SPEEK) and the lithium (Li-SPEEK) and zinc salts (Zn-SPEEK) of sulfonated PEEK (19.2 mol % sulfonation) with N6. The interactions responsible for miscibility
were characterized by Fourier transform infrared (FTIR) spectroscopy. For blends of HSPEEK and N6, miscibility is due to hydrogen bonding between the sulfonic acid and the
amide group. For blends of N6 with the salts of SPEEK the specific interaction involves
a n ion-dipole complex of Li+ with the amide carbonyl or Zn2+ with the amide nitrogen.
The relative strengths of the intermolecular interactions for the three types of blends
increased as the cation was varied in the order: H+ < Li' < Zn2+,and the T,s of the mixtures
increased in the same order. 0 1996 John Wiley & Sons, Inc.
Keywords: Ionomers polyamides PEEK sulfonation complexation blends
INTRODUCTION
Most high-molecular weight polymer pairs are immiscible due to a small combinatorial entropy of
mixing and a generally small or positive enthalpy
of mixing. Polymer blends often do not exhibit their
optimum properties because of poor dispersion and
interfacial mixing. The development of specific intermolecular attractive interactions between two
polymers may sufficiently reduce the enthalpy of
mixing so that miscibility of the polymers is
achieved, and this strategy has been used with increasing frequency in recent years to produce new
miscible blends.'-5 A similar strategy can also lower
the interfacial tension, improve dispersion, and stabilize the size of a dispersed phase in immiscible or
partially miscible mixtures. The use of ionomers for
achieving specific interactions with another polar
polymer is a particularly effective approach for de* To whom correspondence should be addressed.
' Current address: International Paper, Corporate Research
Center, Long Meadow Road, Tuxedo, NY 10987.
Journal of Polymer Science: Part B: Polymer Physics, Vol. 34,1795-1807 (1996)
0 1996 John Wiley & Sons, Inc.
CCC 0887-6266/96/101195-13
veloping miscible or compatibilized polymer blends
from otherwise immiscible polymers.6-"
Poly(e-caprolactam), or Nylon-6, (N6) is an important engineering thermoplastic due to its good
mechanical properties, low coefficient of friction, and
excellent solvent resistance. N6 also has a relatively
low glass transition temperature, ca. 50°C, which
results in poor creep resistance a t elevated temperature. To improve this deficiency, high glass
transition temperature polymers such as poly(oxy1,4-phenyleneoxy-1,4-phenylenecarbonyl-1,4phenylene) (PEEK), polyphenylene ether (PPE),
polycarbonate (PC), or polysulfone (PSF) are often added to N6. Those aromatic polymers, however, are immiscible with N6, and in practice, the
blends are compatibilized by the addition of a third
polymer (i.e., a compatibilizer).
An alternative approach for compatibilizing
blends containing N6 is to chemically modify the
other polymer to promote specific intermolecular
interactions with the polyamide. A number of recent
report^'^-'^ have shown that light sulfonation of
polystyrene greatly enhances its miscibility with N6,
as a result of strong attractive interactions between
the sulfonate and amide groups. Those specific in1795
1796
LU AND WEISS
teractions and, as a consequence, the phase behavior
of the blend may be tailored by varying the extent
of sulfonation and/or judicious choice of the cation.
Sulfonation is one of the most versatile and inexpensive modifications of aromatic polymers." The
degree of sulfonation may be varied over a wide
range, and the sulfonation can be accomplished by
either a postpolymerization reaction or during polymerization if a suitable sulfonated comonomer is
available. With respect to N6 and other polyamides,
compatibilization of blends via intermolecular interactions with sulfonate-containing polymers looks
to be a particularly attractive approach for controlling the morphology and properties.
In this communication, we report on the miscibility of N6 with lightly sulfonated poly(oxy-1,4phenyleneoxy-1,4-phenylenecarbonyl1,4-phenylene) (SPEEK) ionomers. Three representative
counterions, H+,Lit, and Zn2+,were studied, because
of their ability to form different specific interactions
with N6.15 The nature of the specific interactions in
the polymer blends and in blends of model compounds were probed with Fourier transform infrared
(FTIR) spectroscopy.
EXPERIMENTAL
(TSA) with LiOH or ZnAc-ZHzO. N6 with M ,
= 24,000 was purchased from Polysciences, Inc.
Blends of N6 and M-SPEEK were prepared by
mixing the two polymers in solution and then evaporating the solvent. A 2% w/v solution of N6 in mcresol was added dropwise to a stirred 2% w/v solution of M-SPEEK in m-cresol/DMF (50/50). The
blends were cast from solution at 120°C and dried
at 100°C under vacuum for two weeks. Model complexes of N6 an.dp-toluene sulfonates were prepared
by adding an appropriate amount of the salt to a
solution of N6 in m-cresol. Films of the complexes
were cast from the solution at 120°C and dried under
vacuum at 100°C for two weeks.
DSC Measurements
Differential scanning calorimetry (DSC) thermograms were obtained with a Perkin-Elmer DSC-7
using a heating rate of 2O"C/min. To remove any
solvent history effects and absorbed moisture, the
samples were annealed at 250°C under nitrogen for
10 min and then quenched to 30°C before each DSC
heating scan. The glass transition temperature, TBr
was defined as the midpoint of the change in the
heat capacity at the transition and the melting point,
T,, was taken as the maximum of the melting endotherm.
Materials
PEEK with [ q ] = 0.93 dL/g was obtained from ICI
Ltd. Sulfonated PEEK (SPEEK) was prepared according to the procedure described by Bailly et aL21
and by Shibuya and Porter." PEEK in granular
form was dissolved in 96% sulfuric acid to produce
a 2% w/v solution, which was stirred at room temperature for 20 h. The sulfonated polymer was precipitated by dropwise addition of the solution into
a large excess of deionized water at 0 ° C and the
precipitate was filtered and washed several times
with deionized water to remove any residual sulfuric
acid. The sulfonation level was 19.2 mol %, as determined by elemental sulfur analysis. Lithium and
zinc salts of SPEEK were prepared by titrating a
solution of SPEEK in dimethylformamide (DMF)
with lithium hydroxide (LiOH) or zinc acetate dihydrate (ZnAc 2HzO), respectively. The neutralized
polymer was precipitated in a large excess of ethanol,
filtered, and dried under vacuum a t 70°C for a week.
The nomenclature used by us for the ionomers is
M-SPEEK, where M = H+, Li+, or Zn2+. Model
compound salts of Li+-p-toluene sulfonic acid (LiTSA) and Zn2+-p-toluene sulfonic acid (Zn-TSA)
were prepared by neutralizingp-toluene sulfonic acid
FTIR Measurements
Fourier transform infrared (FTIR) spectra were obtained on a Nicolet Model 60SX FTIR spectrometer
by signal averaging a total of 128 scans with a resolution of 1 cm-'. The samples were cast from solution onto NaCl plates and dried first under vacuum
at 100°C for 2 weeks and then for 10 min at 240°C
prior to the FTIR measurements.
RESULTS A N D DISCUSSION
HSPEEK/N6 Blends
DSC thermograms of blends of HSPEEK and N6
are shown in Figure 1. The samples were annealed
at 250°C prior to the DSC scan, so the thermograms
in Figure 1 represent the phase behavior of the
blends at 250°C. Because the T s of the H-SPEEK
and N6 are widely separated, by ca. 140°C, a Tgcriterion was used to assess miscibility of the blend.
That is, a single composition-dependent T,signifies
miscibility and two Tfithat coincide with those of
the neat components indicate immiscilibity of the
SPECIFIC INTERACTIONS AND MISCIBILITY OF BLENDS
I
50
I
100
I
I
150
I
1
200
,
250
Temperature ("C)
Figure 1. DSC heating thermograms of the HSPEEK/
N6 blends quenched from 250°C.
polymers. Two Tgsthat are displaced from those of
the pure component polymers indicate partial miscibility. The DSC thermograms for blends with a
mass fraction of N6 ( w N 6 )2 0.5 exhibited a melting
endotherm for N6. Some crystallization occurred
during the heating scan, as evidenced by the coldcrystallization exotherms in Figure 1.
Values of Tgr T,, and the cold-crystallization
temperature, T,, for the different blends are summarized in Figure 2. For each blend in Figure 1, a
single Tg intermediate between those of the pure
components was observed, which indicates that a t
250"C, H-SPEEK and N6 are miscible over the entire range of composition. Except for a slight anomaly between 0 and 20% N6, which is discussed in
the next paragraph, the Tgof the blends increased
with increasing H-SPEEK concentration. The addition of H-SPEEK to N6 resulted in an increase
in T, and a depression in T,, which is typical for a
miscible blend of a semicrystalline polymer with a
higher T, amorphous polymer. The crystalline component can only crystallize a t a temperature above
Tgof the blend, so the increase of T, is a direct consequence of the elevation of Tgby the addition of
H-SPEEK. The depression of T , may be due to either specific interactions between the component
1797
polymers or a reduction of the N6 crystallite size in
the blend.24 Strong hydrogen bonding interactions
between the amide groups and the sulfonic acid
groups were reported previously for blends of N6
and the acid derivative of SPS,'6,23and a similar
interaction is expected to occur in the N6/H-SPEEK
blends and to be responsible for the observed miscibility.
The DSC thermograms in Figure 1, show a rather
large increase of the T,, from 50 to 75"C, upon the
addition of 10% H-SPEEK to N6 and a decrease of
Tgto 69°C when the H-SPEEK concentration was
increased to 20%, see Figure 2. This anomalous behavior may be a result of partial crystallization of
the N6 during the thermal quench from the annealing temperature of 250°C. Because the HSPEEK is excluded from the crystalline N6 phase,
the actual H-SPEEK concentration in the amorphous phase of the blends exhibiting crystallinity is
higher than the overall concentration. The increase
of Tg to 75°C for the blend containing 10% HSPEEK is much higher than would be expected in
an amorphous 90% N6/10% H-SPEEK blend, and
the Fox equation25predicts that the composition of
the amorphous phase is more like 25% H-SPEEK.
As the total amount of H-SPEEK in the blend increased, less N6 crystallized during the thermal
quench from 250°C so that the composition of the
amorphous phase characterized by the Tgmeasured
0
0
0
A
A
A
A
0
20
40
60
80
100
wt% of SPEEK
Figure 2. Transition temperatures measured from the
DSC thermograms in Fig. 1 for H-SPEEK/NG blends.
1798
LU AND WEISS
by the ensuing DSC heating scan became closer to
the overall composition. For w N 6 < 0.5, no crystallization of the N6 was observed and the Tgsof those
blends were in fair agreement with the Fox equation.
The H-SPEEK enrichment of the amorphous
phase of the blend with w N 6 = 0.9 may have practical
advantages. For that blend, the crystallinity and
melting point of the N6 were only slightly perturbed
by the addition of the H-SPEEK, yet a disproportionate enhancement of Tgwas achieved. That result
suggests that the addition of small amounts of HSPEEK may improve the creep resistance of N6
without diminishing the other desirable mechanical
properties.
ZnSPEEK/N6 Blends
240
1
210 180 -
u
0
W
0
I-
150 120 -
0'
0
0
20
40
60
I
100
80
wt% ZnPEEK
Figure 3. Composition dependence of T, for ZnSPEEK/N6 blends annealed at 250°C.
The Zn-SPEEKING blends appeared to be more
thermally stable a t elevated temperatures than the
N6/H-SPEEK blends. The poorer thermal stability
the carbonyl oxygen and the amide nitrogen are inof the blends involving the free-acid derivative was
volved
in a 1: 1 stoichiometry in a complex with the
consistent with the observation of Bailly et a1.21that
Zn2+
cation.
The two different conclusions may not,
desulfonation occurred at 300°C for the neat freehowever,
be
contradictory in that the presence (or
acid derivative of SPEEK, but not for the sodium
absence)
of
the
amide hydrogen significantly perturbs
salt. For the blends, it is likely that degradation of
the
electronic
structure
of the amide and can conthe N6 was also catalyzed by the degradation of the
ceivably
change
the
nature
of the site for the ionH-SPEEK, though a detailed study of the blend
amide
complex.
The
Zn2+-N
interaction is expected
degradation was not conducted.
to
decrease
as
the
number
of
protons
attached to the
The composition dependence of Tg for the Znamide
nitrogen
decreases,
i.e.,
in
the
order of:
SPEEKIN6 blends is shown in Figure 3. The values
on the abscissa represent the compositions of the
0
0
0
amorphous phase, i.e., the overall composition was
II
II
It
corrected by the amount of N6 crystallinity calcu-C-N-H>
-C-N-R>
-C-N-R
lated by integrating the melting endotherm from the
I
I
DSC thermogram. The single, composition-depenH
H
R'
dent Tgfor the blends indicates that like H-SPEEK,
the Zn-SPEEK is fully miscible with N6 a t 250°C,
lo
2"
3"
though the blends containing the ionomer exhibited
consistently higher TR'The enhancement of the Tg
First, the nitrogen becomes less electronegative as
when the ionomer salt was used in the blend is prethe number of attached hydrogen atoms decreases,
sumably a result of stronger interpolymer interacand, as a result, complexation of a sulfonate cation
to the lone pair of electrons on the nitrogen atom
tions that serve as physical crosslinks. Similar results have been reported for other blends where speis more favorable for the secondary amide in N6
cific complexes are formed between complimentary
than for a tertiary amide such as in an alkylated
functional groups on the two polymer^.^^^^^
polyamide. Second, in an ionomerlN6 blend, the
Previous FTIR and NMR spectroscopy ~ t u d i e s ' ~ ~ ' ~amide proton may hydrogen bond with the carbonyl
oxygen and, therefore, competes with the zinc ion
of blends of N6 and Zn-SPS ionomers showed that
for the oxygen. That may also promote interaction
miscibility resulted from the formation of transition
of the ion with the electrons on the nitrogen. Since
metal conplexes involving the Zn2+cations and the
the methylated polyamide cannot hydrogen bond
amide groups, and there was some evidence that the
metal ion coordinated with the lone pair of electrons
with itself, the carbonyl oxygen is available only for
interaction with the metal cation. Finally, the subon the nitrogen atom. That conclusion conflicts with
a recent investigation28of blends of Zn-SPS and an
stitution of an alkyl group for the amide hydrogen
N,N-methylated Nylon 2,lO that indicated that both
introduces a steric hindrance on the nitrogen that
I
SPECIFIC INTERACTIONS AND MISCIBILITY OF BLENDS
provided by the polyether compared with the hydrocarbon polymer backbone in polystyrene. Nevertheless, a clear shift to lower frequency of the
symmetric S -0 stretching absorbance is seen in
Figure 4 when N6 was added to the Zn-SPEEK ionomer. As with the Zn-SPS ionomer solutions and
blends, the lowering of the frequency of the S-0
stretching band reflects an increased dissociation of
the Zn2+cation and the SO, anion due to complexation of the metal ion with the polyamide. Red-shifts
were also observed for the in-plane bending vibration, 1085 cm-', and the in-plane skeleton vibration,
862 cm-', of the sulfonated-phenyl ring when N6
was added to the Zn-SPEEK ionomer. Those spectral changes are also consistent with a weakening
of the force of the cation on the sulfonate anion
attached to the ring.
Evidence for a Zn2+/amidecomplex was also obtained from the IR regions characteristic of the
amide infrared vibrations. Figure 5 shows the 30003550 cm-' spectral region for the neat N6 and the
blends. Two vibrations in this region, an amide-I1
overtone band at ca. 3060 cm-' and an N-H
stretching band centered at ca. 3300 cm-', are particularly pertinent to the present study. The amideI1 vibration, which occurs a t ca. 1540 cm-', is a coupled mode of C -N stretching and N -H bending,
and it and its overtones are expected to shift to
higher frequency if the amide nitrogen participates
in a complex with the Znz+ ion. Figure 5 confirms
that the amide-I1overtone band shifts progressively
to higher frequency as the Zn-SPEEK concentration
increases.
makes it a less favorable site for an interpolymer
interaction. As a result, it is not inconceivable that
the zinc ions from an ionomer complex differently
with secondary and tertiary poiyamides. What is
clear, however, from other studies of sulfonate ionomer/polyamide blends is that transition metal and
zinc salts form stronger complexes with a polyamide
than does the sulfonic acid or other metal
FTIR spectroscopy also indicates that interactions between the metal cation of the ionomer and
the amide groups of N6 provides the driving force
for the miscibility of the Zn-SPEEKIN6 blends.
Specifically, the perturbations of the stretching vibrations from the sulfonate anion and amide carbony1 and N -H groups are consistent with a Zn2+amide complex. Figure 4 shows the infrared spectra
of the S-0
stretching region for the neat ZnSPEEK and blends with N6. The absorption at 1028
cm-' due to the symmetric stretching vibration of
S -0 is known to be particularly sensitive to the
local environment of the sulfonate gro~p.~',~'
For
example, this absorbance, which occurs at ca. 1045
cm-l for Zn-SPS, shifts to lower frequency when
the ionomer is dissolved in a polar solventz9or when
blended with a p~lyamide.'~
The shift to lower frequency of the symmetric S -0 stretching vibration
results from weakening of the ion-pair due to solvation by the polar solvent or complexation of the
cation with the p~lyamide.~'
The symmetric S -0 stretching vibration for the
Zn-SPEEK occurred at a much lower frequency than
for the Zn-SPS ionomer (1028 cm-l vs. 1045 cm-')
as a consequence of the more polar environment
n
I
1099
1023
946
am
I
794
Wavenumbers(cm- 1 )
Figure 4.
1799
FTIR spectra of the sulfonate stretching region for Zn-SPEEK/N6 blends.
1800
LU AND WEISS
I\\
3 0 X N6
70% N6
\
overtone of arnide 11
I
/
I
3550
341 1
3272
3133
2994
Wavenumbers(cm- I )
Figure 6. FTIR spectra in the N-H
the pure components.
stretching region for Zn-SPEEK/NG blends and
For a semicrystalline aliphatic polyamide like N6,
three N -H stretching vibrations may occur in the
infrared spectrum: at 3300, 3310, and 3450 cm-',
which correspond to hydrogen-bonded N -H
groups in the crystalline phase, hydrogen-bonded
N-H in the amorphous phase and free N-H in
the amorphous phase, re~pectively.~~
Since the neat
N6 was highly crystalline, the absorbance from the
hydrogen-bonded N -H at 3300 cm-' is the dominant spectral feature in Figure 5, though a shoulder
due to hydrogen-bonded N -H in the amorphous
phase can be resolved at ca. 3310 cm-'. No appreciable concentration of free N-H is seen for the
neat N6 in Figure 5. The N -H stretching region
broadens significantly when Zn-SPEEK is blended
with the N6, which is a consequence of several factors, including lower crystallinity, solvation of the
self-hydrogen bonding of the polyamide and formation of an intermolecular complex between the
amide groups and the Zn2+ion.
The broadening of the N -H stretching band on
the high frequency side is due primarily to the decrease of the crystallinity of the N6 by the addition
of Zn-SPEEK. According to the DSC results, blends
containing greater than 60% Zn-SPEEK were completely amorphous. In addition to depressing the
crystallinity, the Zn-SPEEK dissociates the hydrogen-bonding and increases the free amide concentration, which increases the N -H stretching component at 3450 cm-' in the FTIR spectrum. For the
blend containing 70% Zn-SPEEK, the N-H
stretching absorbance in Figure 5 extends to 3480
cm-l, which suggests a broad distribution of local
environments of the amide groups in the amorphous
polymer, including an appreciable concentration of
free amide groups.
The broadening of the N -H stretching band on
the low frequency side by the addition of the ionomer
to N6 may be explained by the replacement of hydrogen bonds between the amide groups with transition metal complexation and/or hydrogen bonds
between the amide and zinc sulfonate groups. The
N -H stretching vibration could shift to lower frequency if hydrogen bonds between the N -H and
sulfonate oxygen were stronger than the self-hydrogen bonding of the amide groups. However, this explanation is ruled out, because a similar shift should
then be observed with the Li-SPEEKING blends,
which it was not (as will be discussed in a later section). A more plausible explanation for the red-shift
of the N-H stretching vibration is coordination
of the Zn2+ion with the nitrogen atom. This explanation has foundation in the literature of amidemetal ion complexes, which shows that coordination
of the ion to the amide nitrogen lowers the N-H
stretching frequency, while coordination to the
amide oxygen increases the f r e q u e n ~ y . ~ ~ - ~ ~
Difference spectra of the amide-I and amide-I1
spectral region are given in Figure 6 for the ZnSPEEK/N6 blends. The difference spectra were ob-
SPECIFIC INTERACTIONS AND MISCIBILITY OF BLENDS
707. ZnSPEEK
1801
/ I,
5 0 X ZnSPEEK
I760
1680
1600
1520
1i 4 0
Wavenumbers(cm-I )
Figure 6. FTIR spectra of the amide-I and amide-I1 region for Zn-SPEEK/N6 blends
and the pure components. The blend spectra are difference spectra (see text).
tained by subtracting the spectrum of the neat ZnSPEEK from the spectra of the blends, and they
represent the sum of the polyamide contributions
to the blend plus any changes due to interactions of
the components. The amide-I band is primarily due
to the C =0 stretching vibration of the amide group
and the amide-I1 band is a coupled mode vibration
involving N -H stretching and C -N bending. As
discussed earlier, the amide-I1 absorption appears
a t ca. 1540 cm-' for the pure N6 and shifts to higher
frequency in the blend, as a consequence of the formation of a Zn2+-amidecomplex. For the neat N6,
the amide-I absorption consists of a peak a t ca. 1640
cm-' due to the amide groups in the crystalline phase
and a shoulder at ca. 1655 cm-' due to the amide
groups in the amorphous phase. When Zn-SPEEK
was blended with the N6, the crystallinity of the
latter decreased and a corresponding increase of
the intensity of the 1655 cm-' band relative to
that of the 1640 cm-l band occurred (Fig. 6). The
blend containing 70% ionomer was completely
amorphous and in that case, a single broad absorption a t ca. 1650 cm-' is seen in the spectrum
in Figure 6. In addition to the changes in the relative intensities of the 1640 cm-' and 1655 cm-'
bands, a new shoulder developed on the low frequency side of the amide-I absorption in the
blends. From analysis of the FTIR spectra of
model complexes, discussed in the following section, the shoulder a t ca. 1608 cm-' was assigned
to a Zn2+-amidecomplex, and i t provides direct
spectroscopic evidence for the association of the
amide group with the Zn2+cation.
Zn-TSA/N6 Complexes
The band assignments for the ionomerlN6 complex
were determined by evaluating the FTIR spectra of
model complexes formed from Zn-TSA and N6. Figure 7 shows the amide-I and amide-I1 spectral region
for the complexes as a function of the molar ratio
of amide groups and Zn++ions. A distinct new absorption develops at ca. 1596 cm-' upon addition of
Zn-TSA to N6 and that band grows in intensity,
while the amide-I band at 1640 cm-' disappears as
the Zn2+/amide ratio increases. The absorption a t
1596 cm-' was assigned to a Zn2+-amidecomplex.
A similar new absorption was observed as a lower
frequency shoulder on the amide-I band in the ZnSPEEKIN6 blends, c.f., Figures 6 and 7, though in
that case the shoulder occurred a t a higher frequency, ca. 1608 cm-'. The differences in the frequency of the Zn2+-amide complexes in the two different blends can probably be explained by differences in the dielectric constant of the molecule to
which the sulfonate group was attached (i.e., polyether versus toluene).
Because the intensity of the 1596 cm-' band is
proportional to the concentration of the complex in
the blend, the complexation stoichiometry may be
1802
LU AND WEISS
1506 ,
I571
2: 1
1
.s:1
0.5: 1
Zn-TSA
-------1799
9
1686
I573
l4GO
13 8
Wavenumbers(cm- 1 )
Figure 7. FTIR spectra of the amide-I and amide-I1 region for N6 and Zn-TSA/N6
complexes.
estimated from the dependence of the band intensity
on the blend composition. The 1596 cm-' band increased with increasing Zn-TSA concentration until
the molar ratio of Zn2+/amidewas 1 : 1. In addition,
the amide-I band at 1640 cm-' disappeared when
the Zn2+/amide ratio was greater than 1 : 1. Those
results indicate that the complex stoichiometry was
one Zn2+ ion per amide group. A similar stoichiometry was concluded for Zn-SPSIN6 based on the
transition temperatures and relaxation times of the
blends.14
As with the Zn-SPEEKING blends, the amide-I1
band of N6 at 1542 cm-' shifted to higher frequency
upon addition of Zn-TSA. It reached a constant frequency of 1571cm-' when the Zn2+/amideratio was
1 : 1, which also supports the conclusion of a 1 : 1
complex.
Figure 8 shows the spectra in the N -H stretching region for the of Zn-TSAIN6 complexes. The
model complexes exhibit similar changes in the
N-H
stretching region as the Zn-SPEEKING
blends. The addition of Zn-TSA to N6 significantly
broadened the N-H
stretching band, which is
consistent with the result described above for the
Zn-SPEEKIN6 blends. Above a ratio of Zn2+/amide
= 1,no further change of the N-H
stretching band
was observed, which indicates that all the amide
groups were complexed by the Zn2+ions a t a Zn2+/
amide ration = 1. Blending N6 with Zn-TSA also
shifted the amide-I1 overtone band from 3080 to
3110 cm-', which again was consistent with the
spectral changes observed for the Zn-SPEEKING
blends.
LiSPEEK/NC Blends
Like the Zn-SPEEKING blends, the Li-SPEEKIN6
blends annealed at 250'C exhibited a single, composition-dependent Tgthat indicated complete miscibility of the two polymers for all blend compositions. The Tgs of the Li-SPEEKIN6 blends are
plotted against the overall blend composition in
Figure 9. Although all three derivatives of MSPEEK (i.e., H-SPEEK, Li-PEEK, and ZnSPEEK) were miscible with N6, the choice of the
cation did have a notable effect on the Tgand presumably the physical properties of the blend. For
similar blend compositions, Tg of the blends increased with the cation in the order of H+ < Li+
< Zn2+,c.f. Figures 2, 3, and 9. The differences in
Tgresulted from differences in the strength of the
ion-amide interactions, which also increased in the
order of H+ < Li+ < Zn++.
Figure 10 compares the spectra of the amide-I
and amide-I1 region for the Li-SPEEKIN6 blends
and the pure component polymers. As discussed
earlier, the strong amide-I absorption at 1640 cm-'
in the spectrum of N6 is primarily due to C = O
SPECIFIC INTERACTIONS AND MISCIBILITY OF BLENDS
Zn-TSA r\,
1803
/
I
3500
3375
3250
3006
3125
Wavenumbers( cm- 1 )
Figure 8. FTIR spectra in the N-H
stretching region for Zn-TSA and Zn-TSA/N6
complexes.
stretching of hydrogen-bonded amide and the weak
shoulder at ca. 1655 cm-' is due to free, unbound
amide groups. When Li-SPEEK was added to the
N6, the 1640 cm-' band broadened and shifted to
higher frequency as a result of replacement of the
hydrogen-bonded carbonyl by a complex with the
Li+ ion. In contrast with the Zn-SPEEKING blends,
a low frequency shoulder was not evident on the
amide-I absorption for the Li-SPEEKIN6 blends.
The complexation of the Li+with the polyamide also
shifted the amide-I1 band, which is at 1540 cm-I for
the pure N6, to higher frequency.
Similar changes of the amide-I and amide-I1 absorptions of N6 were observed for the model complexes of N6 with Li-TSA (Fig. 11). Both bands
shifted to higher frequencies when Li-TSA was
added to N6, and the stoichiometry appeared to be
1 : 1 as judged by the invariance of the spectra for
Li+/amide > 1.
The difference in the effect of ion-amide complexation for the Li-TSA and Zn-TSA blends is
noteworthy. For the latter, formation of the complex
resulted in a 54 cm-' shift to lower frequency (1640
to 1596 cm-') of the amide-I absorption, while for
the Li-TSA complex the amide-I absorption shifted
10 cm-' to higher frequency (1640 to 1650 cm-'),
c.f., Figures 7 and 11. The much larger change in
the amide-I absorption for the Zn-TSA blend indicates that the Zn2+-ion forms a stronger complex
with the polyamide than does the Li+, which is consistent with the DSC results for the change of Tg
For both complexes, a constant absorption frequency
was observed for all blend compositions, rather than
a gradual change of the vibration frequency, which
indicates that the complex had a distinct chemical
identity-as opposed to simply a steady change of
the local environment of the amide group. The difference in the direction of the shift for the two different ions suggests a fundamental difference in the
nature of the complex formed. The most likely specific interaction for the Li+ ion is with the carbonyl
oxygen of the amide group." Although the nature
of the Zn2+-amidecomplex is less certain, as discussed earlier, we believe that coordination occurs
at the amide nitrogen.
The FTIR spectra for the Li-SPEEKIN6 blends
showing the S -0 stretching region of the sulfonate
anion are given in Figure 12. The spectral features
4
240
n
!?
W
0)
I-
-
0
20
40
60
80
100
w t % LiPEEK
Figure 9. Composition dependence of T8 for the LiSPEEK/N6 blends.
1804
LU AND WEISS
Amide I
Aniide II
1600
Wavenumbers ( c m - 1 )
1400
Figure 10. FTIR spectra of the amide-I and amide-I1 region for Li-SPEEKLNG blends
and the pure components.
are similar to what was observed for Zn-SPEEK/
N6. The symmetric stretching vibration of the sulfonate anion occurs at ca. 1034 em-' for the Li-
SPEEK and shifts to ca. 1024 cm-' for the blends
with N6. That change is consistent with a weakening
of the polarization of the S - 0 bond by the local
Amide I
1700
1600
1500
Wovenumbers ( c m - 1 )
1400
Figure 11. FTIR spectra of the amide-I and amide-I1 region for Li-TSA and LiTSA/
N6 complexes.
SPECIFIC INTERACTIONS AND MISCIBILITY OF BLENDS
1100
1805
1000
1050
W a v e n t i m b e i - s (cln- 1 )
Figure 12. FTIR spectra of the sulfonate stretching region for Li-SPEEK/N6 blends
and the pure components.
electrostatic field of the cation,30which occurs as a
consequence of dissociation of the Li+--O,S ion-pair
when the Li+ coordinates with the polyamide. For
similar reasons, the other IR bands associated with
the sulfonate anion, such as the in-plane bending
vibration (ca. 1082 cm-') and in-plane skeleton vibration (ca. 865 cm-') of the substituted phenyl ring
also shift to the lower frequencies as N6 is blended
with Li-SPEEK.
Significant changes in the N -H stretching region were also observed for Li-SPEEKIN6 blends,
Figure 13. The amide-11overtone band broadens and
shifts from ca. 3100 to ca. 3120 cm-' and the N -H
stretching vibration centered at ca. 3300 cm-' for
o v e r t o n e o t unirdr II
LISPEEK
I
3550
1
34 1 I
3272
3133
2994.
Wavenumbcrs(cm- I )
Figure 13. FTIR spectra of the N-H
stretching region for Li-SPEEK/N6 blends.
1806
LU AND WEISS
the neat N6 also broadens and shifts to higher frequency for the blends. Those spectral changes are
consistent with complexation of the Lit with the
amide oxygen, as well as with the changes in the
self-hydrogen bonding of the polyamide and the decreasing crystallinity of the N6 in the blend as discussed earlier. In addition, the broad high frequency
tail of the N -H stretching vibration indicates that
there was an appreciable concentration of free, unbonded amide groups in the blends.
CONCLUSIONS
Sulfonation of PEEK effectively improves its miscibility with an aliphatic polyamide such as N6.
Miscibility is due to the development of strong specific interactions between the amide and sulfonate
groups, and blends involving the free acid or the Li+
or Zn2+salts of SPEEK were miscible over the entire
range of composition at 250°C. The choice of the
cation, however, has a significant effect on the
strength of the specific interactions, which is directly
manifest by the Tgof the blends. The strength of
the complex and the blend Tgincreases as the cation
is varied in the order of H+ < Li+ < Zn2+.For blends
involving H-SPEEK, miscibility is due to hydrogen
bonding between SOBH and NHCO, while for the
salt derivatives of SPEEK, specific coordination
complexes develop between the metal ion and the
amide group. Li+ complexes to the amide carbonyl.
It is less certain as to whether Zn2+coordinates to
the carbonyl oxygen or the amide nitrogen. In either
event, however, both the oxygen and the nitrogen
are involved with the complex structure, and the
polarization of the nitrogen atom is much greater
than for the Li+-amide complex.
The addition of SPEEK to N6 effectively increases the Tgof the latter, and if the concentration
of the ionomer is kept relatively low, a disproportionate rise in the Tgmay be accomplished without
adversely affecting the melting point and the crystallinity of the N6. For example, by adding 10%(wt )
of H-SPEEK to N6, Tgincreases by ca. 30°C.
The results of this investigation suggest that the
extent of compatibility and the physical properties
of PEEK/polyamide blends may be controlled by
sulfonation of PEEK and judicious choice of the
cation. Although the sulfonation level was not varied
in this investigation, results for other systems, e.g.,
SPS ionomers blended with polyamides, suggest that
additional control of the compatibility may be attained by changing the degree of sulfonation of the
PEEK.
This research was supportedby a grant from the Polymers
Program of the National Science Foundation (DMR
9400862 ) .
REFERENCES AND NOTES
1. P. Smith and A. Eisenberg, J. Polym. Sci., Polym.
Lett. Ed., 21, 223 (1983).
2. M. M. Coleman, A. M. Lichkus, and P. C. Painter,
Macromolecules, 2 2 , 586 ( 1989).
3. M. M. Coleman, J. F. Graf, and P. C. Painter, Specific
Interactions and the Miscibility of Polymer Blends,
Technomic Publishing, Lancaster, PA, 1991.
4. E. M. Pearce, T. K. Kwei, and B. Y . Min, J. Macromol
Sci., Chem., A 2 1 , 1181 (1984).
5. E. P. Douglas, K. Sakurai, and W. J. MacKnight,
Macromolecules, 2 4 , 4575 (1991).
6. A. Eisenberg and M. Hara, Polym. Eng. Sci., 2 4 , 1 3 0 6
( 1984 1.
7. P. Smith, M. Hara, and A. Eisenberg, in Current Topics in Polymer Science, II, R. M. Ottenbrite, L. A.
Utracki, and S. Inoue, Eds., Hanser, New York, 1987;
p. 255.
8. X. Zhang and A. Eisenberg, J. Polym. Sci. Part B:
Polym. Phys., 2 8 , 1841 ( 1 9 9 0 ) .
9. M. Hara and A. Eisenberg, Macromolecules, 2 0 , 2 1 6 0
( 1987 1.
10. K. Sakurai, E. P. Douglas, and W. J. MacKnight,
Macromolecules, 25, 4506 ( 1992).
11. A, Sen, R. A. Weiss, and A. Garton, in Multiphase
Polymers: Blends and Ionomers, L. A. Utracki, and
R. A. Weiss, Eds., ACS Symp. Ser. 395, American
Chemical Society, Washington, DC, 1989, p. 353.
12. X. Lu and R. A. Weiss, Macromolecules, 2 4 , 4381
(1991 1.
13. X. Lu and R. A. Weiss, Macromolecules, 2 5 , 6185
(1992).
14. T. K. Kwei, Y. K. Dai, X. Lu, and R. A. Weiss, Macromolecules, 2 6 , 6583 ( 1993).
15. R. A. Weiss and X. Lu, Polymer, 35, 1963 (1994).
16. A. Molnar and A. Eisenberg, Polym. Commn., 32,
1001 ( 1991 ) .
17. Z . Goa, A. Molnar, F. G. Morin, and A. Eisenberg,
Macromolecules, 2 5 , 6460 ( 1992).
18. A. Molnar and A. Eisenberg, Macromolecules, 2 5 ,
5774 (1992).
19. P. Rajagopalan, J-S. Kim, H. P. Brack, X. Lu, A.
Eisenberg, R. A, Weiss, W. M. Risen, Jr., J. Polym.
Sci. Part B: Polym. Phys., 3 3 , 4 9 5 (1995).
20. R. Taylor, Chemical Kinetics, Vol. 13, Reactions of Aromatic Compounds, c . H. Bamford, c. F. H. Tipper,
Eds., Elsevier, Amsterdam, 1972, pp. 56-77.
21. C. Bailly, D. J. Williams, F. E. Karsz, and W. J.
MacKnight, Polymer, 2 8 , 1009 ( 1987).
22. M. Shibuya and R. S. Porter, Macromolecules, 25,
6495 (1992).
SPECIFIC INTERACTIONS AND MISCIBILITY OF BLENDS
23. X. Lu and R. A. Weiss, Proc. Mat. Res. SOC.,2 1 5 , 29
(1991).
24. J. D. Hoffman, Polymer, 2 3 , 6 5 6 ( 1982).
25. T. G. Fox, Bull. Am. Phys. Soc., 1 , 1 2 3 (1956).
26. J. M. Rodriguez-Parada and V. Percec, Macromolecules, 1 9 , 5 5 (1986).
27. X. Lu, and R. A. Weiss, Macromolecules, 25,6185 (1992).
28. Y. Feng, R. A. Weiss, and A. Schmidt, (submitted).
29. J. J. Fitzgerald, and R. A. Weiss, in Coulombic Interactions in Macromolecular Systems, A. Eisenberg, and
F. E. Bailey, Eds., ACS Symp. Ser. 302; American
Chemical Society, Washington, DC, 1986, p. 35.
30. G. Zundel, Hydration and Intermolecular Interaction,
Academic Press, New York, 1969.
1807
31. D. J. Skrovanek, P. C. Painter, and M. M. Coleman,
Macromolecules, 1 9 , 699 ( 1986).
32. F. A. Cotton, in Modern Coordination Chemistry, J.
Lewis and R. G. Wilkins, Eds., Interscience, New
York, 1960, p. 361.
33. J. Fujita, K. Nakamoto, and J. Kobayashi, J. Am.
Chem. Soc., 7 8 , 3295 (1956).
34. C. MacDonald and C. J. Willis, Can. J. Chem., 5 1 ,
732 ( 1973).
Received December 4,I995
Revised February 15, 1996
Accepted February 22, 1996