was used for the ethylene content quantification within an EP block copolymer
[73]. The gradual increase in the CH 3 /CH 2 ratio across the bimodal MMDs is
observed for the first three fractions eluting at 60
C, 80
C and 90
C, respectively.
This indicates the higher propylene content in the lower molar mass component; see
Fig. 2.15. The ethylene content decreases gradually from the higher molar mass
side of the distribution until it reaches zero within the lower molar mass region, as
indicated by the ratios of the 720 cm
À1 /1,162 cm
À1 bands. This is a clear indication
that ethylene is only present in the higher molar mass components and the band at
1,378 cm
À1 represents the methyl groups in PP only.
There is a visible difference in the compositions of the lower and high molar
mass components of the bimodal distribution. PP homopolymers are the sole
component of the lower molar mass region, in contrast to the high molar mass
part which is composed of EPCs with varying monomer distributions. The
ethylene-rich copolymers appear on the higher molar mass side. The propylene
content increases towards the lower molar mass side of the distribution. The 100
C
fraction forms the transition between blocky copolymers and iPP fractions eluting
at higher temperature, as predicted by
13 C-NMR. The Gram–Schmidt curve
constructed from the CH 3 /CH 2 ratio shows lower values for regions of higher
molar mass (low elution volume) compared to the low molar mass region,
indicating the differences in the propylene content in both regions of the MMD.
This is a clear sign that the propylene content is lower in the region of higher molar
masses. The results are in good agreement with the ratio of 720 cm
À1 /1,163 cm
À1 ,
which decreases to zero in the direction of higher elution volumes. The presence of
EPC in the higher molar mass shoulder in the 100
C fraction is therefore confirmed
by SEC-FTIR analysis. The two melt endotherms in each of these fractions determined by DSC analysis suggest the presence of both crystalline ethylene and
propylene segments. The specific crystalline entities for both monomers are
associated with specific IR bands; therefore, the construction of ethylene and
propylene crystallinity profiles should be possible from SEC-FTIR. The
998 cm
À1 and 841 cm
À1 bands are associated with long repeating monomer units
in the crystalline 3 1 helix of PP [74–77]. The short helix segments are associated
with the 972 cm
À1 band of the FTIR spectrum. There is a linear correlation between
the intensities of the 998 cm
À1 and 841 cm
À1 bands and the density of PP as a
measure of its crystallinity [78]. PP tacticity can, therefore, be determined by the
ratio of the 998 cm
À1 and 972 cm
À1 absorption bands, providing the degree of
spectral crystallinity in PP.
FTIR spectroscopy also provides information on the relative crystallinity of
ethylene segments in EPCs along with propylene segments. The 720 cm
À1 band
originates from long methylene sequences. With the increase in crystallinity of PE,
the intensity of the 730 cm
À1 component increases at the cost of splitting of the
720 cm
À1 band [79, 80]. The band at 730 cm
À1 is recognized as a true crystallinity
band [75]. Therefore, the relative crystallinity in PE is related to the ratio of the
band intensities at 720 cm
À1 and 730 cm
À1 [80–82]. The ratios of 998 cm
À1 /
972 cm
À1 and 730 cm
À1 /720 cm
À1 are constructed across the Gram–Schmidt
34
2 Crystallization-Based Fractionation Techniques
[73]. The gradual increase in the CH 3 /CH 2 ratio across the bimodal MMDs is
observed for the first three fractions eluting at 60
C, 80
C and 90
C, respectively.
This indicates the higher propylene content in the lower molar mass component; see
Fig. 2.15. The ethylene content decreases gradually from the higher molar mass
side of the distribution until it reaches zero within the lower molar mass region, as
indicated by the ratios of the 720 cm
À1 /1,162 cm
À1 bands. This is a clear indication
that ethylene is only present in the higher molar mass components and the band at
1,378 cm
À1 represents the methyl groups in PP only.
There is a visible difference in the compositions of the lower and high molar
mass components of the bimodal distribution. PP homopolymers are the sole
component of the lower molar mass region, in contrast to the high molar mass
part which is composed of EPCs with varying monomer distributions. The
ethylene-rich copolymers appear on the higher molar mass side. The propylene
content increases towards the lower molar mass side of the distribution. The 100
C
fraction forms the transition between blocky copolymers and iPP fractions eluting
at higher temperature, as predicted by
13 C-NMR. The Gram–Schmidt curve
constructed from the CH 3 /CH 2 ratio shows lower values for regions of higher
molar mass (low elution volume) compared to the low molar mass region,
indicating the differences in the propylene content in both regions of the MMD.
This is a clear sign that the propylene content is lower in the region of higher molar
masses. The results are in good agreement with the ratio of 720 cm
À1 /1,163 cm
À1 ,
which decreases to zero in the direction of higher elution volumes. The presence of
EPC in the higher molar mass shoulder in the 100
C fraction is therefore confirmed
by SEC-FTIR analysis. The two melt endotherms in each of these fractions determined by DSC analysis suggest the presence of both crystalline ethylene and
propylene segments. The specific crystalline entities for both monomers are
associated with specific IR bands; therefore, the construction of ethylene and
propylene crystallinity profiles should be possible from SEC-FTIR. The
998 cm
À1 and 841 cm
À1 bands are associated with long repeating monomer units
in the crystalline 3 1 helix of PP [74–77]. The short helix segments are associated
with the 972 cm
À1 band of the FTIR spectrum. There is a linear correlation between
the intensities of the 998 cm
À1 and 841 cm
À1 bands and the density of PP as a
measure of its crystallinity [78]. PP tacticity can, therefore, be determined by the
ratio of the 998 cm
À1 and 972 cm
À1 absorption bands, providing the degree of
spectral crystallinity in PP.
FTIR spectroscopy also provides information on the relative crystallinity of
ethylene segments in EPCs along with propylene segments. The 720 cm
À1 band
originates from long methylene sequences. With the increase in crystallinity of PE,
the intensity of the 730 cm
À1 component increases at the cost of splitting of the
720 cm
À1 band [79, 80]. The band at 730 cm
À1 is recognized as a true crystallinity
band [75]. Therefore, the relative crystallinity in PE is related to the ratio of the
band intensities at 720 cm
À1 and 730 cm
À1 [80–82]. The ratios of 998 cm
À1 /
972 cm
À1 and 730 cm
À1 /720 cm
À1 are constructed across the Gram–Schmidt
34
2 Crystallization-Based Fractionation Techniques