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A nonlinear rheological model combining elastic, viscous, and yielding phenomena is developed in order to describe the rheological behavior of materials which exhibit a yield stress. A key feature of the formulation is the incorporation of a recoverable strain; it has a maximum value equal to the critical strain at which the transition from an elastic solid-like response to a viscous shear thinning response occurs. An analysis is presented to enable determination of all the model parameters solely from dynamic measurements which are easily accessible experimentally. A rigorous correlation, analogous in form to the Cox–Merz rule, is shown to exist between the steady shear viscosity and the complex dynamic viscosity in terms of a newly defined ‘‘effective shear rate.’’ Experimental data obtained for a 70 vol % suspension of silicon particles in polyethylene indicate agreement with theoretical predictions for both the dynamic and steady shear behavior.

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Several alkoxy/aryloxy-substituted phosphazene polymers [P(OR)2=N],, where R = C,H,, CH2CF,, C,H lo, were prepared by the reaction of polydichlorophosphazene with their corresponding sodium salts. The polydichlorophosphazene was obtained by the solution polymerization of hexachlorocyclotriphosphazene in 1,2,4-trichlorobenzene. Sulfamic acid and ammonium sulfamate were used as catalysts. Apparently, sulfamic acid functions as a catalyst through its acid group in some decomposed form. New catalysts, p-toluenesulfonic acid and sulfobenzoic aicd, have been developed for this solution polymerization. The polymerization favors a cationic mechanism. A promoter, CaSO, . 2 H,O, was found to speed up the polymerization reaction. Effect of several parameters such as dilution, catalyst concentration, and promoter concentration on the properties of the final polymer were investigated. The polymers were characterized by differential scanning calorimetry, gel permeation chromatography, and "P solution NMR spectroscopy.

Rheological properties of selected poly(organo)phosphazenes have been studied using capillary rheometry. Melt viscosities of polymers were calculated as a function of shear stress and shear rate. Thermal stability was also studied. In the range of shear rate studied, all polyphosphazenes showed shear thinning behavior. The power law model was fitted to the data to get the power law index and the consistency index. Poly[bis(phenoxy)phosphazene] showed a Newtonian plateau at low shear rates whereas poly[bis(trifluoroethoxy)phosphazene] and poly[bis(p‐phenylphenoxy)phosphazene] which exhibited liquid crystalline character were shear thinning even at low shear rates. Solid state capillary extrusion of polyphosphazenes was found to be more successful in fiber formation than other “state‐of‐the‐art” processes, such as gel‐spinning. The molecular weights of all polyphosphazenes synthesized were found to be too low for, Couette fiber spinning. Chemical, physical, and morphological studies were made on all fibers prepared. Many investigative techniques, such as X‐ray diffraction, differential scanning calorimetry (DSC), density measurements, scanning electron microscopy (SEM), optical microscopy, solution nuclear magnetic resonance (NMR) spectroscopy, and gel permeation chromatography (GPC) analysis are featured in this paper as characterization tools.