Application of rheological techniques for investigations of polymer branched structures

Rheological properties, such as the zero shear rate viscosity eta(0), and the fluidity difference Delta phi 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 eta(0) and Delta phi on molecular weight (M), molecular weight distribution (MWD) and LCB. In particular, the exponent b(1) of the MVP function written as log(Delta phi(.) eta(0)) = log B + log[(eta(0)(.)(gamma) over dot)(b1) (.)q(b2) (.)G(b3)] 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 PIE and PMMA, have also been shown for comparison of MVP linear master dependencies. It has been found that the exponent b(1) 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 b(1), the higher the amount of branches. The quantitative dependence of b(1) on branching degrees can be found, e.g., for PC b(1) = 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. (C) 1998 Elsevier Science B.V. All rights reserved.