2.2.1 Characterization of Homogeneous Ethylene–Octene
Copolymers [103]
For the last 30 years LLDPE has been produced mainly using multiple-site
(Ziegler–Natta, ZN) catalysts. These copolymers have broad (multimodal) CCDs,
which has a strong impact on product performance. The CCD of olefin copolymers
is also referred to as short chain branching distribution (SCBD).
The fractionation of EO copolymers by TREF has been discussed in Sect. 2.1.1.
It has been shown that ZN LLDPEs contain a highly crystalline fraction of HDPE
and fractions of very low crystallinity that have high comonomer contents.
2.2.1.1 Aim
In the present application, the CCD of homogeneous EO copolymers shall be
analysed by CRYSTAF. Such LLDPEs are typically produced by using a singlesite (constrained geometry) catalyst. The correlation between crystallization temperature and comonomer content shall be investigated and the data shall be used for
calibrating CRYSTAF/TREF. Finally, the behaviour of these homogeneous
LLDPEs shall be compared to a commercial ZN LLDPE.
2.2.1.2 Materials
• Polymers. A series of 17 samples of EO copolymers produced by Dow Chemical
in a solution process with a constrained geometry catalyst, sample densities
0.868–0.935 g/cm
3 , melt indexes (at 190
C, with 2.16 kg, according to ASTM
D1238) are 0.5–30 dg/min.
2.2.1.3 Equipment
• CRYSTAF system. Commercial CRYSTAF instrument model 100 (Polymer
Char, Valencia, Spain).
• Detector. Built-in dual wavelength IR detector with heated flow-through micro
cell at 150
C.
• Solvent. TCB.
• Crystallization protocol. Crystallization between 90
C and 30
C (in selected
cases between 90
C and 5
C) at a rate of 0.2
C/min.
• Sample concentration. 30 mg in 30 mL TCB.
2.2.1.4 Preparatory Investigations
As a first step of the investigation, the homogeneous EO copolymers were
measured. Figure 2.28 shows the CRYSTAF curves of three representative
samples. As expected, the samples exhibit monomodal and narrow crystallization
profiles, which are a clear indication of their narrow CCDs.
The CRYSTAF results of all samples are summarized in Table 2.5 and compared
to other analytical data.
The calculation of the weight and number average crystallization temperatures
T w and T n , respectively, and the parameters measuring the broadness of the CCD,
are as follows:
50
2 Crystallization-Based Fractionation Techniques
Copolymers [103]
For the last 30 years LLDPE has been produced mainly using multiple-site
(Ziegler–Natta, ZN) catalysts. These copolymers have broad (multimodal) CCDs,
which has a strong impact on product performance. The CCD of olefin copolymers
is also referred to as short chain branching distribution (SCBD).
The fractionation of EO copolymers by TREF has been discussed in Sect. 2.1.1.
It has been shown that ZN LLDPEs contain a highly crystalline fraction of HDPE
and fractions of very low crystallinity that have high comonomer contents.
2.2.1.1 Aim
In the present application, the CCD of homogeneous EO copolymers shall be
analysed by CRYSTAF. Such LLDPEs are typically produced by using a singlesite (constrained geometry) catalyst. The correlation between crystallization temperature and comonomer content shall be investigated and the data shall be used for
calibrating CRYSTAF/TREF. Finally, the behaviour of these homogeneous
LLDPEs shall be compared to a commercial ZN LLDPE.
2.2.1.2 Materials
• Polymers. A series of 17 samples of EO copolymers produced by Dow Chemical
in a solution process with a constrained geometry catalyst, sample densities
0.868–0.935 g/cm
3 , melt indexes (at 190
C, with 2.16 kg, according to ASTM
D1238) are 0.5–30 dg/min.
2.2.1.3 Equipment
• CRYSTAF system. Commercial CRYSTAF instrument model 100 (Polymer
Char, Valencia, Spain).
• Detector. Built-in dual wavelength IR detector with heated flow-through micro
cell at 150
C.
• Solvent. TCB.
• Crystallization protocol. Crystallization between 90
C and 30
C (in selected
cases between 90
C and 5
C) at a rate of 0.2
C/min.
• Sample concentration. 30 mg in 30 mL TCB.
2.2.1.4 Preparatory Investigations
As a first step of the investigation, the homogeneous EO copolymers were
measured. Figure 2.28 shows the CRYSTAF curves of three representative
samples. As expected, the samples exhibit monomodal and narrow crystallization
profiles, which are a clear indication of their narrow CCDs.
The CRYSTAF results of all samples are summarized in Table 2.5 and compared
to other analytical data.
The calculation of the weight and number average crystallization temperatures
T w and T n , respectively, and the parameters measuring the broadness of the CCD,
are as follows:
50
2 Crystallization-Based Fractionation Techniques