Production of LPE/BPE blends using homogeneous binary catalyst system: influence of the polymerization parameters on polymer properties

Linear polyethylene/branched polyethylene blends (LPE/BPE) were prepared using the homogeneous binary catalyst system composed by Ni(α-diimine)Cl2 (1) (α-diimine=1,4-bis(2,6-diisopropylphenyl)-acenaphthenediimine) and rac-ethylenebis(IndH4)ZrCl2 (2) (IndH4=4,5,6,7-tetrahydro-1-η5-indenyl) activated with methylaluminoxane in hexane at three different polymerization temperatures (0, 30 and 50 °C) and by varying the zirconium loading molar fraction (xZr). The polymerization runs carried out at 30 °C have shown that the productivity decreases linearly with xZr. On the other hand, at 0 and 50 °C, a non-linear dependence was observed between the xZr and the productivity. The molecular weight of the LPE/BPE blends varied from 222 to 470×103 g mol−1 with polydispersities around 2.0. Differential scanning calorimetry results showed that the dependence of the Tm values with respect to the xZr it is higher for the LPE/BPE blends produced at 0 °C. Dynamic mechanical thermal analysis shows the formation of different polymeric materials where the stiffness varies according to the xZr. The surface morphology of the BPE/HDPE blends produced at 30 °C revealed a low miscibility between the PE phases resulting in the formation of a ‘cobweb structure’ (for xZr=0.25) after etched with hot o-xylene.