Analysis of the chemical composition distribution of ethylene/α-olefin copolymers by solution differential scanning calorimetry: an alternative technique to Crystaf

A series of ethylene/1-hexene copolymers synthesized with a metallocene catalyst with varying comonomer contents but constant molecular weights were analyzed with crystallization analysis fractionation (Crystaf), solid state differential scanning calorimetry (solid state DSC) and solution differential scanning calorimetry (solution DSC). Experimental solution DSC exotherms were compared to Crystaf profiles obtained under similar crystallization conditions. At the same cooling rates (0.1 °C/min), considerable differences were found for samples with low levels of short chain branching although the discrepancy became less significant with increasing branching. Very good agreement was found between the Crystaf profiles of metallocene copolymers obtained at a cooling rate of 0.1 °C/min and solution DSC exotherms of samples crystallized at the rate of 0.01 °C/min. Good agreement was also observed between the Crystaf and solution DSC profiles of a Ziegler–Natta linear low-density polyethylene (LLDPE) sample when crystallized at the same cooling rate of 0.2 °C/min. In conclusion, solution DSC is a useful technique for simulating profiles obtained by Crystaf analysis, although very slow analysis times must be used for samples with less than 4 mol% comonomer.