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Z. Dobkowski

A method for determining the degree of branching of macromolecules from basic rheological measurements

Polimery 1999, No 3, 208


DOI: dx.doi.org/10.14314/polimery.1999.208


Summary

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).


Keywords: rheological properties, degree of branching of polymers, polycarbonate, polydimethylsiloxane.

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