Newtonian viscosities in a homodisperse melt

As explained in Section Vm. 1 the viscosity (i)) tqipears as the product of an elastic modulus E and a relaxation time r . In the reptation picture E is independent of N. while Tf IV , and rf should thus scale like A/ for a polymer melt of linear chains. 

What hiqipens if we go to branched chains This has been discussed recently by Graessley et al. Two effects come into play  

After a close scrutiny of the experimental data, Graessley et al. were led to assume that relaxation is controlled by reptation, and that the reptation times for the branched species increase exponentially, as in eq. (VIII.23). Again the complete solution to these problems will probably involve experiments on dilute mixtures of branched chains in a linear matrix and vice-versa. 

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