Characterization of Polyketone Copolymer by High Speed DSC

a p p l i c at i o n N o t e
Thermal Analysis
Wim M. Groenewoud
Eerste Hervendreef 32
5232 JK ‘S Hertogenbosh
The Netherlands
Nik Boer
PerkinElmer, Groningen
The Netherlands
Phil Robinson
Thermal Analysis Consultant
Ruston Services Limited
Staffordshire, United Kingdom
Characterization of
Polyketone Copolymer
by High Speed DSC
The aliphatic polyketone copolymer
(PK copolymer) is a perfectly alternating
copolymer of ethylene and carbon
monoxide.1 It exhibits many desirable
engineering thermoplastic properties,
such as a high tensile yield stress and
an excellent impact performance. Its high degree of chemical resistance and
superior barrier properties make this polymer an interesting, new thermoplastic
for engineering applications.
After a washing and drying procedure, the reactor product consists of a white,
semi-crystalline powder, soluble only in a few exotic solvents, like hexafluoroisopropanol (HFIPA) and meta-cresol. The crystalline phase of this polymer is
built of orthorhombic unit cells with a polymer chain at each corner and one in
the center. These polymer chains crystallize into two different modifications the
alpha and the beta modification. The alpha modification changes into the beta
form material at temperatures higher than about 120 °C. The beta form material,
which is the dominant unit cell for the (unoriented) PK copolymer, fuses at
about 250 °C. Lommerts et al,2 calculated the dimensions of both cell types.
Alpha form a = 6.91 Å, b = 5.12 Å, c = 7.60 Å; cryst. density = 1.382 g/cm3. For
the beta form, a = 7.97 Å, b = 4.76 Å, c = 7.57 Å; cryst. density = 1.297 g/cm3.
The density increase obtained when the standard beta phase
material is converted into the alpha phase material might
improve the barrier properties even more (the structure and
extent of the crystalline phase are important barrier-properties
determining parameters). To see if and how the beta phase
material could be changed into the alpha phase material PK
copolymer was studied.
PerkinElmer Pyris™ 1 DSC
Polymerization-solvent induced and pressure/shear forces
induced alpha crystallinity effects prove to be (partly)
irreversible after heating through the alpha/beta crystal transition, indicated by Tm*. A third method found, thermally
induced alpha crystallinity, annealing at a temperature just
below the melting of the beta crystalline phase, proved to
be completely reversible.3 So, this method was used to make
PK copolymer systems with high alpha/beta crystal ratios.
A series of three such samples were put aside to measure
possible effects of storage time on the alpha/beta ratio.
Sample mass:
1 mg (approximately)
The conventional DSC analysis of these samples using a
PerkinElmer® DSC 7 had many problems. The three main
problems were:
- Uncertainty about Tm1 (max) value, (cross-linking reactions,
possibly already started during the fusion, might influence
the measured Tm1 values).
- Uncertainty about proper Tm1 values in connection with
clearly present re-crystallization effects during the main
fusion process.
- Investigation of the amorphous phase, i.e. determination
of the Tg-value by conventional DSC was not possible for
PK copolymer.
Recent developments in high speed DSC provide many
advantages over conventional DSC. HyperDSC® is the premier
fast scan DSC technique from PerkinElmer. It requires a DSC
instrument with an extremely fast response time and very
high resolution. It allows very fast linear heating and cooling
scanning (up to 500 °C/min) over a broad temperature range.
Not only does HyperDSC provide higher sensitivity, but it can
also suppress kinetic events during scanning, thus analyzing
the sample as received. During the discussions about the
advantages of the HyperDSC, we realized that this improved
technique might give the answers we were still looking for.
The samples used for this study and the sample treatment as
a function of temperature and time are schematically shown
in Appendix I. The following experiment conditions were
used to measure these samples in 2005:
Heating/cooling rate: 300 °C/min
Number of scans: First and second heating scans taken
for each sample
Temperature range:
-100 °C to +300 °C
The HyperDSC was calibrated for temperature and enthalpy
responses using high purity indium and lead. The systems’
base-line was checked before and after the measurements
(Figure 1).
In 1993, the data was obtained by using a PerkinElmer
DSC 7 with a scanning rate of 20 °C/min.
Experiment and calculated values
This study was started with a number of scouting experiments
to check our reported Tm1(max) value of 258 °C ±1 °C
(20 °C/min).3 A reactor powder sample measured at a heating
rate of 300 °C/min resulted in Tm1(powder) = 258.6 °C and
256.6 °C. Hence, the Tm1 value determination proved that it
was not hampered, or hardly hampered by possible crosslinking effects.
Figure 1. System baseline before and after the experiments (red: before, blue:
Normalized Heat fow Endo Up (Wg)
Figure 2 shows the first and second heating scan results
measured on sample 1 in 2005. Both curves clearly illustrate
that the alpha phase crystallinity present in this sample
(see alpha/beta crystal transition between about 100 °C and
150 °C) completely disappeared at the start of the second
heating scan. But then, the second scan clearly showed a
shifted fusion process of the beta crystalline phase to lower
temperatures. This raised the question; might both effects
be coupled? We started to summarize both fusion effects in
Tm and Hf values (results shown in Table 1) and used Figures 3
and 4 to get a better look at the fusion processes. Figure 3A
shows the fusion endotherms of the three samples at the
standard heating rate in 1993. Figure 3B gives the same
results, but measure at 300 °C/min. in 2005. Both figures
show that the fusion endotherms of the samples 2 and 3 in
1993 were clearly influenced by recrystallization effects
during the fusion process. These effects were (barely) present
in the three endotherms measured at a high rate in 2005.
Heat flow (W/g)
Sample 3
Sample 2
Sample 2
Temperature (°C)
Figures 4A and B show the alpha/beta crystal transitions
of these samples. Figure 4A shows the expected result, i.e.
no annealing – no alpha crystallinity – no alpha/beta crystal
transition in sample 3 (1993), besides, an increasing strength
of the alpha/beta crystal transition with increasing annealing
times. The alpha/beta crystal transitions measured in 2005 at
a high heating rate are shown in Figure 4B. The strength of
the crystal transition of the two annealed samples (1 and 2)
are not only increased, but that the non-annealed reference
sample 3 is also now showing a clear crystal transition. Thus,
during the longtime storage at 20 °C of this sample, beta
crystallinity has been partly changed into alpha crystallinity
due to the release of built-in stress during the compression
molding procedure. This important aspect will be discussed
later on separately.
Sample 1
Sample 2
Sample 3
Temperature (°C)
Figure 4A. The alpha phase fusion effects of the systems 1, 2 and 3 (in 1993),
i.e. heating rate 20 °C/min.
Sample 1
Figure 3B. The beta phase fusion effects of the systems 1, 2 and 3 (in 2005),
i.e. heating rate 300 °C/min.
Heat flow (W/g)
Sample 1
Sample 3
Figure 2. First and second heating scans measured on sample 1. (in 2005).
Red curve is initial heating and blue curve is second heating.
Temperature (°C)
Figure 3A. The beta phase fusion effects of the systems 1, 2, and 3 (in 1993),
i.e. heating rate 20 °C/min.
The linear relation Tm1/Hf* was used in the same way to
calculate the corrected Tm1 values for both samples 2 and
3 (1993). The corrected Tm1 value of sample 2 (1993) was
calculated at 251.8 °C. The corrected Tm1 value of sample 3
(1993) was calculated at ≤ 249.4 °C.
Sample 1
Sample 2
Normalized Heat fow Endo Up (Wg)
These four calculated values are also listed in Table 1, with
the warning: calculated values.
Sample 3
Calculation of beta phase Tm1 and Hf1 values based on the
alpha phase Tm* value.
Temperature (°C)
Figure 4B. The alpha phase fusion effects of the systems 1, 2 and 3 (in 2005),
i.e. heating rate 300 °C/min.
Table 1. High and low heating rate results measured on PK
Hf* = 0.7200 x (Tm*) – 72.5678
Sample Code Alpha Cryst. Phase
Hf * J/g
Tm * °C
Beta Cryst. Phase
Tm1 C
Hf1 J/g
Tm1 = 0.4668 x (Hf*) + 249.4099
1. 1993**
Hf1 = 0.8497 x (Hf*) + 111.7243
withTm1 and Tm* : °C
1. 2005***
2. 1993
251.8 *
2. 2005
3. 1993
249.4 *
3. 2005
Hf1 and Hf* : J/g and
*** (2005) high, i.e. 300 °C/minute heating rate experiments.
In order to check the consistency of all fusion effects measured,
we first tried to find a manner to correct for the recrystallization effects during the fusion of samples 2 and 3 (1993). It
soon became clear that especially strong coupling between
the alpha/beta fusion effects offered correction possibilities.
The Hf1 values of the four other samples were plotted as a
function of Hf*. The linear relation fitting these values was
extrapolated to Hf* = 0.0 with a Hf1 value of 112.8 J/g. This
value of 112.8 was subsequently changed in small steps
between 114.0 and 110.0 to find the Hf1 value for Hf* = 0.0,
giving the highest correlation factor value. Using this value
as a ‘calculated’ data point, an ‘optimized’ Hf1/Hf* relation
was calculated i.e.:
Hf1 = 0.8497 x (Hf*) + 111.89 (n = 5. Rval. = 0.9537)
100 °C < Tm* < 125 °C
It is important to realize that these equations only hold for
compression molded PK copolymer systems.
corrected by calculation, see text.
** (1993) low, i.e. 20 °C/minute heating rate experiments.
Substitution of Hf* = 0.0 for sample 3 (1993) resulted in a
corrected Hf1 value of ≤ 111.7, i.e. 112 J/g instead of the
experimental value 110.6 J/g. Substitution of Hf* = 5.1 J/g
for sample 2 (1993) resulted in a corrected Hf1 value of
116 J/g instead of the experimental value of 119.1 J/g.
The differences in the Tm1 and Hf1 values listed in Table 1 are
not straightforward. Hence, we tried to calculate these values
to see if they fit in one model. The used model is simple:
assuming that the Tm* values are known, it calculates the
other three parameters i.e., the Hf* , Tm1 and Hf1 values with
three derived equations:
Subsequently, the four Tm* values listed in Table 1 with
corresponding experimental Tm1 and Hf1 values were used
to calculate the fusion values of their beta crystalline phase,
see Table 2. The comparison of the calculated values with
the reported measured values is satisfactory. It indicates
that the measured differences in Tm1 and Hf1 of both important
properties are correct. Continuation of this research is
necessary to obtain further/better understanding of this
fascinating behavior. But, in fact these results obtained
with experimental data:
• differ in time more than twelve years
• are measured at different locations and by different persons
• are performed on different DSC systems
and are, in our eyes the best proof of the excellent quality,
high stability and reliability of PerkinElmer’s Thermal Analysis
Table 2. Testing the consistency of the results of high and
low heating rate DSC experiments performed in 1993 and
Beta Phase Tm1 Values
Sample Code
Tm1 (calc.)°C
Tm1 (meas.)°C
|DT| °C
252 1.1
258 0.7
257 0.3
3.(2005)252.2 252.7 0.5
|DT| °C average
Beta Phase Hf1 Values
Sample Code
Hf1 (calc.) J/g
Figure 5. The DSC Tg value determination of sample 1 at 300 °C/min (in 2005).
Hf1 (meas.) J/g
|DHf| J/g
1.(1993)118.5 116.1 2.4
1.(2005)126.2 126.9 0.7
2.(2005)126 126.10.1
3.(2005)116.8 118.2 1.5
|DT| °C average
This result is much better than we ever measured for such
semi-crystalline polymers. We do think that a proper optimization in terms of sample mass, sample shape and sample
pre-treatment3 will improve these results even more.
Summary and conclusions
The glass-rubber transition
The Tg value determination of high crystalline polymers by
DSC is, for most systems, not possible, or at least difficult.
Earlier, we reported our attempts to determine the Tg values
of PK co- and terpolymer by conventional DSC. The conclusion
then was the DSC Tg value determination of PK co- and
terpolymers is only possible on PK terpolymers after a proper
thermal pre-treatment. The DSC Tg (onset) value reported
for these systems was 4 °C ±3 °C.3
The heat flow/temperature curves of the present three
samples were blown-up to see if any Tg effect was present.
A clear Tg effect was measured for the systems 1 and 3
(2005), see Figure 5. For system 2 (2005) only the Tg onset
was detected. So we found:
1. (2005) DSC Tg (onset) = 7 °C
Two simple HyperDSC heating scans on three PK copolymer
samples provided more information about the amorphous
and crystalline phases of this high crystalline polymer than
a lot of standard DSC heating rate measurements did in the
past. The high heating rate measurements (300 °C/min)
dismissed the doubts that the reported maximum Tm1 value,
i.e. 258 °C, and the alpha- and beta-phase fusion effects
were measured without any hampering due to recrystallization effects during both processes. The results of both
the recent high rate and the old low rate measurements fit
perfectly in the proposed alpha/beta fusion model. Besides,
Tg effects were clearly detected in these scans without any
pre-treatment (this is rare for such high crystalline polymers).
The results of these measurements show that the HyperDSC
technique is really the most effective and most sensitive DSC
technique available at the moment for the characterization
of both the crystalline and the amorphous phase of a
polymeric system.
2. (2005) DSC Tg (onset) = 2 °C
3. (2005) DSC Tg (onset) = 9 °C
1.E. Drent, European Patent 121,96 (Shell), 1984.
2.B.J. Lommerts et al., J. of Pol. Sc. : Part B: Polymer Physics,
Vol. 31, p. 1319 – 1330 (1993).
3.W.M. Groenewoud: Characterization of Polymers by
Thermal Analysis, Elsevier Science Amsterdam/New York,
ISBN:0-444-50604-7 (2001).
Appendix I: Thermal history of investigated PK copolymer samples
Reactor powder PK copolymer (Carilon E) – MDU batch 91.091
Tm1 = 258 ±1 °C*
Hf1 = 152 ±6 J/g*
II. Sample sheet molding i.e. Compression molded for 2.5 min. at 280 °C
III. Annealing procedure
10 min. at 240 °C
DSC sample 1. (1993)
6 min. at 240 °C
DSC sample 2. (1993)
no annealing
reference DSC sampe 3. (1993)
IV. Storage time 1993-2005 storage in darkness at 20 °C and 50% R.H.
DSC sample 1. (2005)
DSC sample 2. ( 2005)
DSC sample 3. (2005)
* reported average values; specific batch values 257.0 °C / 151.8 J/g
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