Precisely differentiate the Zimm, Rouse, and reptation models.

a$.$ What is the essential difference between the Rouse and Zimm models for the

viscoelastic properties of solutions.

b$.$ Contour length fluctuations and constraint release both accelerate chain

relaxation; what is the crucial difference in these two processes?

c$.$ What is the distinction between $M_{c,e}$ and $M_e?$