Application of rheological techniques for investigations of polymer branched structures

Rheological properties, such as the zero shear rate viscosity η0 and the fluidity difference Δϕ between the Newtonian and non-Newtonian conditions, have been applied for investigations of branched structures of polymers. Branching parameters that characterise the long chain branching (LCB) of macromolecules have been determined using the multivariable power function (MVP) for the dependence of η0 and Δϕ on molecular weight (M), molecular weight distribution (MWD) and LCB. In particular, the exponent b1 of the MVP function written as log(Δϕ·η0)=log B+log[(η0·γ̇)b1·qb2·Gb3] enables distinguishing linear and branched polymer structures. Experimental results for PDMS, PP, and PC have been discussed. Literature data for these polymers, as well as for PIB and PMMA, have also been shown for comparison of MVP linear master dependencies. It has been found that the exponent b1 is equal to 0.76–0.79 (approximately) for linear polymers, and it is lower than 0.76 for branched ones. The lower the value of b1, the higher the amount of branches. The quantitative dependence of b1 on branching degrees can be found, e.g., for PC b1=0.30+0.47G. The MVP linear master dependencies are parallel for each type of polymer considered. It is assumed that their shift can be dependent on some specific constant for a polymer material. The investigations to find such a polymer material constant should be continued, and more experimental data are needed, in particular for polymer branched structures.