homopolymer, EP segmented polymer and EP random copolymer. The mechanical
properties of the different materials were correlated with the molecular
architectures and phase structures of the products. Amer and van Reenen reported
on the TREF fractionation of iPP to obtain fractions with different molar masses but
similar tacticities [34]. The DSC results of the fractions indicated that the configuration (tacticity) and the molar mass of the PP strongly affected the crystallization
behaviour.
Cross-fractionation techniques such as SEC-TREF or TREF-SEC were used
for the deconvolution of bivariate MMD/CCD distributions of polyolefin
copolymers. The results were used to identify the number of active catalyst sites
and the relation of the type of active sites with the microstructure of polyolefins
produced with multiple-site catalysts [35]. Model ethylene-1-butene and ethylene-1-octene copolymers were used to validate the approach. The correlation of
molecular structure and mechanical properties of ethylene-1-hexene copolymer
film grade resins produced by a metallocene catalyst by varying the molar mass
and branching distribution was studied by Alamo and co-workers [36]. Molar
mass fractionation was achieved by solvent/non-solvent techniques, while fractionation with respect to 1-hexene content was obtained by P-TREF. The hyphenation of TREF with SEC-FTIR offered a simple alternative to conventional and
time-consuming methods for characterizing the compositional heterogeneity of
IPCs [37].
The idea to combine different polyolefin fractionation methods to address the
multiple molecular distributions was developed by Nakano and Goto; they combined TREF and SEC to address the bivariate distribution in chemical composition
and molar mass [38]. The resulting instrument was the first fully automated
instrument that combined the chemical composition fractionation by TREF and
the subsequent molar mass analysis of the TREF fractions by SEC.
When combining SEC and TREF there are, in principle, two options:
SEC-TREF or TREF-SEC. The SEC-TREF approach was followed by Aust
et al. [39] to analyse a medium density PE, while Faldi and Soares used TREFSEC for the fractionation of a LLDPE [40]. Shan et al. developed a custom-built
TREF-SEC instrument [41] which was used later by Gillespie et al. for SEC-TREF
experiments [42]. Yau demonstrated the potential of a 3D-SEC-TREF apparatus
which was used for the investigation of polyolefin microstructures [43]. A refractive index (RI) detector, a LS detector and a dual wavelength IR detector were used
as online detectors, as shown in Fig. 2.6.
Monrabal and co-workers [44] pioneered the development of a user-friendly
automated cross-fractionation apparatus (TREF-SEC) to fully characterize
polyolefins with bivariate distributions; see Fig. 2.7. Short chain branching
distributions have been analysed as a function of molar mass. The instrument was
based on the design of a TREF 300 unit. The concentration detector employed is a
dual band IR4 infrared detector. Further online detectors, such as methyl-sensitive
IR sensors, Visco and LS detectors, can be added to enhance the amount of
information.
2.1 Temperature Rising Elution Fractionation
19
properties of the different materials were correlated with the molecular
architectures and phase structures of the products. Amer and van Reenen reported
on the TREF fractionation of iPP to obtain fractions with different molar masses but
similar tacticities [34]. The DSC results of the fractions indicated that the configuration (tacticity) and the molar mass of the PP strongly affected the crystallization
behaviour.
Cross-fractionation techniques such as SEC-TREF or TREF-SEC were used
for the deconvolution of bivariate MMD/CCD distributions of polyolefin
copolymers. The results were used to identify the number of active catalyst sites
and the relation of the type of active sites with the microstructure of polyolefins
produced with multiple-site catalysts [35]. Model ethylene-1-butene and ethylene-1-octene copolymers were used to validate the approach. The correlation of
molecular structure and mechanical properties of ethylene-1-hexene copolymer
film grade resins produced by a metallocene catalyst by varying the molar mass
and branching distribution was studied by Alamo and co-workers [36]. Molar
mass fractionation was achieved by solvent/non-solvent techniques, while fractionation with respect to 1-hexene content was obtained by P-TREF. The hyphenation of TREF with SEC-FTIR offered a simple alternative to conventional and
time-consuming methods for characterizing the compositional heterogeneity of
IPCs [37].
The idea to combine different polyolefin fractionation methods to address the
multiple molecular distributions was developed by Nakano and Goto; they combined TREF and SEC to address the bivariate distribution in chemical composition
and molar mass [38]. The resulting instrument was the first fully automated
instrument that combined the chemical composition fractionation by TREF and
the subsequent molar mass analysis of the TREF fractions by SEC.
When combining SEC and TREF there are, in principle, two options:
SEC-TREF or TREF-SEC. The SEC-TREF approach was followed by Aust
et al. [39] to analyse a medium density PE, while Faldi and Soares used TREFSEC for the fractionation of a LLDPE [40]. Shan et al. developed a custom-built
TREF-SEC instrument [41] which was used later by Gillespie et al. for SEC-TREF
experiments [42]. Yau demonstrated the potential of a 3D-SEC-TREF apparatus
which was used for the investigation of polyolefin microstructures [43]. A refractive index (RI) detector, a LS detector and a dual wavelength IR detector were used
as online detectors, as shown in Fig. 2.6.
Monrabal and co-workers [44] pioneered the development of a user-friendly
automated cross-fractionation apparatus (TREF-SEC) to fully characterize
polyolefins with bivariate distributions; see Fig. 2.7. Short chain branching
distributions have been analysed as a function of molar mass. The instrument was
based on the design of a TREF 300 unit. The concentration detector employed is a
dual band IR4 infrared detector. Further online detectors, such as methyl-sensitive
IR sensors, Visco and LS detectors, can be added to enhance the amount of
information.
2.1 Temperature Rising Elution Fractionation
19