Star polymer shear thinning

The programme on branched polymers is driven both by long-standing puzzles in the extension-hardening (yet shear thinning) of commercial branched polymers and the radically different rheology seen in model mono-disperse branched melts such as stars. Recent extensions of the tube model... 

Polymers are normally classified into four main architectural types linear (which includes rigid rod, flexible coil, cyclic, and polyrotaxane structures) branched (including random, regular comb-like, and star shaped) cross-linked (which includes the interpenetrating networks (IPNs)) and fairly recently the dendritic or hyperbranched polymers. I shall cover in some detail the first three types, but as we went to press very little DM work has been performed yet on the hyperbranched ones, which show some interesting properties. (Compared to linear polymers, solutions show a much lower viscosity and appear to be Newtonian rather than shear thinning [134].) Johansson [135] compares DM properties of some hyperbranched acrylates, alkyds. and unsaturated polyesters and notes that the properties of his cured resins so far are rather similar to conventional polyester systems. 

Finally, the parameters from the dynamic moduli and from shear thinning are cross-correlated, namely for each set of parameters the parameter a of the lower-frequency form has a well-defined power-law dependence on Gio, G20, or tjq, respectively, the dependences each extending over many orders of magnitude in the corresponding independent variable, leading to expressions such as Eq. 13.18. The correlations are very nearly the same for linear and for star polymers. 

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