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-Ne wtonian conditions, have been applied for investigations of branched s tructures of polymers. Branching parameters that characterise the long chain branching (LCB) of macromolecules have been determined using th e 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 pol ymer structures. Experimental results for PDMS, PP, and PC have been d iscussed. Literature data for these polymers, as well as for PIE and P MMA, have also been shown for comparison of MVP linear master dependen cies. 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 bran ched ones. The lower the value of b(1), the higher the amount of branc hes. The quantitative dependence of b(1) on branching degrees can be f ound, e.g., for PC b(1) = 0.30 + 0.47G. The MVP linear master dependen cies are parallel for each type of polymer considered. It is assumed t hat their shift can be dependent on some specific constant for a polym er material. The investigations to find such a polymer material consta nt should be continued, and more experimental data are needed, in part icular for polymer branched structures. (C) 1998 Elsevier Science B.V. All rights reserved.