Block copolymer viscosity comparison

Kraus has studied the steady flow and dynamic viscosity of the following branched butadiene t) ene block copolymers (88)3, (88)3, (88)4 in comparison with 888 and 888 copolymers. He has found higher viscosities (at constant molecular weight and total styrene content for polymers terminated by styrene blocks) for the former inespective of branchii, but for copolymers of equal molecular weight the viscosity is smaller for branched than for linear copolymer. Kraus has also studied the effect of free polybutadiene molecules on the viscoelastic behaviour of branched (88)4 block copolymers which consist of styrene domains in a butadiene matrix and verified De Gennes s theory of reptation ... 

Figure 6.14. Comparison of the temperature dependence of viscosity above the polystyrene for AB block copolymer 63 and that predicted from the WLF expression (Erhardt et aL, 1969).

Rheological studies of solutions of these polymers in distilled water clearly identified viscosity enhancement due to the presence of the hydrophobic tert butylstyrene endblocks. Comparison with homopolymer and random copolymers of similar composition and molecular weight demonstrated the increased viscosification with the block configuration. The block polymer solutions were also observed to solubilize toluene with a marked increase in the solution viscosity. These results are interpreted as the result of polymer intermolecular association through the hydrophobic blocks similar to micellization of surfactants. 

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