High density polyethylene complex viscosity

Strands that terminate with a branch point at both of its ends can neither reptate nor completely retract. Relaxation of such strands presumably occurs by more complex, hierarchical processes discussed by McLeish (1988b). Here we simply note that the presence of branch points at both ends of a strand leads to much more strain hardening in extensional flows (Bishko et al. 1997 McLeish and Larson 1998). Low-density polyethylenes (LDPEs), which are highly branched, are well known for their extreme strain hardening behavior in extensional flows (Meissner 1972 Laun 1984) (see Fig. 3-39). The steady-state shear viscosity, as a function of shear rate, seems to be little affected by long-chain branching, however. 

Table 5.8 lists propylene polymerization data for some of the complexes shown in Figure 5.12. Varieties of other polymer products have been prepared using the D/A-bridged complexes. For example the (Flu)(Cp)ZrCl2 complexes (22a-b) produce ultra-high molecular weight (UHMW) polyethylene with intrinsic viscosities as high as 13.5 d/g. The D/A metallocenes are also effective catalysts for the copolymerization of a-olefins with ethylene to produce medium to ultta-low density polyethylene products. ... 

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