DSC endotherms. As it can be seen, there is a very good
agreement between the Cw values calculated from DSC
endotherms with the SCB concentrations obtained by 13C
NMR analysis.
In order to further evaluate this method, the authors
have also used the data presented by Starck in 1996 [25]. In
this paper, Starck used some commercial LLDPE polymers
the specifications of which are presented in Table 3. In the
same manner as before, the simple DSC endotherms of
these samples presented in Starck’s paper were sliced and
the method described above was used for determination of
SCB content of these series of samples. The results are given
in Table 4. It should be mentioned that, since in Starck’s
paper the branch content of metallocene samples (M2 and
M3) had not been measured, the SCB of these samples are
calculated from the mole% of co-monomer according to
ASTM D5017-96. As it can be seen in Table 4, the metallocene
samples have lower BDI (narrower branch distribution)
than Ziegler–Natta ones which is due to the
existence of single active site in metallocene catalysts
instead of multiple active sites of Z–N catalysts.
In order to better compare the results, in Fig. 2 the SCB
contents determined by CNMR (or TREF) are plotted against
the results obtained by DSC endotherms for all of Starck’s
samples in addition to ours. As it can be seen, most of the
points fall on the X ¼ Y line which denotes good agreement
between these two methods. The discrepancy in some
points can be attributed to the experimental errors.