sequential gas-phase polymerization in the presence of a Ziegler–Natta catalyst
[51]. A complex mixture of reaction products is formed that ranges from amorphous
random EPCs to crystalline iPP. This wide range of reaction products is attributed
to the sequential polymerization procedure and the heterogeneous nature of the
catalyst. Different monomer sequence distributions and sequence lengths lead to
varying degrees of crystallinity. Accordingly, EPCs are semi-crystalline to varying
extents [52–54] and are also referred to as EP block copolymers [55–57], although
this terminology is misleading, regarding the nature of the mixture of end products
obtained.
The distribution of ethylene and propylene sequences, the sequence lengths and
the tacticities determine the final properties of IPC. Therefore, the detailed characterization of IPCs is an important subject, focusing on fractionation as well as
spectroscopic analysis. Structural parameters of bulk EPCs have been investigated
using
13 C-NMR as a method of choice [58]. The information on comonomer
contents, distribution of monomers and tacticity could also be obtained by FTIR
[59]. DSC is the method of choice to study the melting and crystallization behaviour
of IPC. DSC is able to distinguish random copolymers from blends and block
structures found in EPCs [60]. The complexity of IPC products makes fractionation
techniques an integral part of the characterization protocol. Separation of the
different components have been achieved by analytical and preparative TREF
[52, 55, 57, 61, 62]. The hyphenation of TREF fractionation with
13 C-NMR, DSC
and FTIR allows a comprehensive characterization of impact PP but it is a timeconsuming procedure.
2.1.2.1 Aim
The present application describes the preparative TREF fractionation of a commercial IPC that is followed by a detailed investigation of the molecular structure of the
fractions. In addition to NMR, DSC and SEC as the standard analytical methods,
coupled SEC-FTIR shall be used to analyse the chemical composition as a function
of molar mass.
2.1.2.2 Materials
• Polymers. Non-stabilized commercial IPC from SASOL Polymers (Secunda,
South Africa) with the following bulk properties: ethylene content 10.5 mol%,
isotacticity 88.8 % (mmmm), M w 354 kg/mol, molar mass dispersity 3.18.
2.1.2.3 Equipment
• TREF system. In-house built preparative TREF apparatus. For crystallization,
3 g of polymer, ca. 2 wt% Irganox 1010 (Ciba Speciality Chemicals,
Switzerland) and 300 mL of solvent were placed in a glass reactor and dissolved
at 130
C. The reactor was transferred to an oil bath maintained at 130
C. As the
crystallization support, pre-heated sea sand (white quartz; Aldrich, South Africa)
was added to the reactor. The reactor was cooled at a rate of 1
C/h. A stainless
steel column was packed with the crystallized mixture and transferred to a
modified GC oven. The temperature of the oven was increased at a steady rate
26
2 Crystallization-Based Fractionation Techniques
[51]. A complex mixture of reaction products is formed that ranges from amorphous
random EPCs to crystalline iPP. This wide range of reaction products is attributed
to the sequential polymerization procedure and the heterogeneous nature of the
catalyst. Different monomer sequence distributions and sequence lengths lead to
varying degrees of crystallinity. Accordingly, EPCs are semi-crystalline to varying
extents [52–54] and are also referred to as EP block copolymers [55–57], although
this terminology is misleading, regarding the nature of the mixture of end products
obtained.
The distribution of ethylene and propylene sequences, the sequence lengths and
the tacticities determine the final properties of IPC. Therefore, the detailed characterization of IPCs is an important subject, focusing on fractionation as well as
spectroscopic analysis. Structural parameters of bulk EPCs have been investigated
using
13 C-NMR as a method of choice [58]. The information on comonomer
contents, distribution of monomers and tacticity could also be obtained by FTIR
[59]. DSC is the method of choice to study the melting and crystallization behaviour
of IPC. DSC is able to distinguish random copolymers from blends and block
structures found in EPCs [60]. The complexity of IPC products makes fractionation
techniques an integral part of the characterization protocol. Separation of the
different components have been achieved by analytical and preparative TREF
[52, 55, 57, 61, 62]. The hyphenation of TREF fractionation with
13 C-NMR, DSC
and FTIR allows a comprehensive characterization of impact PP but it is a timeconsuming procedure.
2.1.2.1 Aim
The present application describes the preparative TREF fractionation of a commercial IPC that is followed by a detailed investigation of the molecular structure of the
fractions. In addition to NMR, DSC and SEC as the standard analytical methods,
coupled SEC-FTIR shall be used to analyse the chemical composition as a function
of molar mass.
2.1.2.2 Materials
• Polymers. Non-stabilized commercial IPC from SASOL Polymers (Secunda,
South Africa) with the following bulk properties: ethylene content 10.5 mol%,
isotacticity 88.8 % (mmmm), M w 354 kg/mol, molar mass dispersity 3.18.
2.1.2.3 Equipment
• TREF system. In-house built preparative TREF apparatus. For crystallization,
3 g of polymer, ca. 2 wt% Irganox 1010 (Ciba Speciality Chemicals,
Switzerland) and 300 mL of solvent were placed in a glass reactor and dissolved
at 130
C. The reactor was transferred to an oil bath maintained at 130
C. As the
crystallization support, pre-heated sea sand (white quartz; Aldrich, South Africa)
was added to the reactor. The reactor was cooled at a rate of 1
C/h. A stainless
steel column was packed with the crystallized mixture and transferred to a
modified GC oven. The temperature of the oven was increased at a steady rate
26
2 Crystallization-Based Fractionation Techniques