"Using melt rheology and solution viscometry to determine the degree of long chain branching"
: Proc. XIVth Int. Congr. on Rheology, Seite(n) PM03-1 - PM03-3, 8-2004
Using melt rheology and solution viscometry to determine the degree of long chain branching
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Proc. XIVth Int. Congr. on Rheology
Low degrees of long chain branching in otherwise linear polymers are known to affect the viscoelastic properties of melts tremendously. Rheological characteristics like the zero shear viscosity  of polymer melts and the zero concentration intrinsic viscosity [] of polymer solutions depend differently on the molar mass and on long chain branching. For linear polymers the relationship between the weight average of the molar mass Mw and the rheological parameters  and [] are well known. In case of low levels of long chain branching the influence of branching on these parameters is assumed to be additive and linear with respect to  the number of branches per 1000 monomer units. The pertinent equations  = c Mw3.4 +  and [] = k Mwa -  are evaluated with the aid of data of commercial grade polypropylenes. Starting with  = 0 the iterative calculation of Mw and  leads to the final result very fast, because the value of  is much smaller than that of k Mwa. As the influence of the molar mass distribution on  and [] is known to be moderate the coefficients of these equations will hold for slightly different distributions.