A method for determining the degree of branching of macromolecules from basic rheological measurements
Polimery 1999, No 3, 208
Dynamic viscosity (h) data measured in relation to shear rate (g) (or frequency w) are used to determine the zero shear rate viscosity (h0), and a multivariable power function [1, 2] in modified coordinates is used to distinguish between linear and branched polymer molecules and to establish the degree of branching (G). The steps for qualitative evaluation of G are: (i) measure h in relation to g or w; (ii) evaluate h0; (iii) use modified coordinates: у = Df · h0 and x = h0· g or h0· w; (iv) regress data (log у = log В + b1 log x) to find b1 and (v) evaluate G using as a guidance: b1 = 0.76—0.79 and b1 < 0.76 indicate a linear and a branched polymer, resp.; the lower the b1 the higher the average number of branching points per macromolecule. The steps for quantitative evaluation of G include (i)—(v) and: (vi) plot b1 vs. G by using standard samples of well-known G to ascertain the calibration dependence b1 = f(G); (vii) calculate G from the known b1 and the calibration plot of step (vi). Examples are given for polycarbonate (PC) and polydimethylsiloxane (PDMS).
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