Viscoelastic Properties of Narrow-Distribution Poly(methyl methacrylates)

Abstract

The viscoelastic properties of two series of poly(methyl methacrylates) (PMMA) with different tacticities and very narrow molecular weight distributions were measured in the molten state at different temperatures by means of oscillatory rheometry. Zero-shear viscosity η0, steady-state shear compliance Je°, and plateau modulus GN° were obtained from the resulting master curves for the storage modulus G‘ and loss modulus G‘‘. Relaxation time spectra h(τ) were calculated by a nonlinear regularization method and could be used to determine the terminal relaxation time τ0. The molecular weight and polydispersity dependence of these parameters agrees with existing empirical rules for linear amorphous polymers. Stereoregularity, however, has a great influence on η0 and τ0. The entanglement molecular weight Me and the critical molecular weight Mc seem to vary with the tacticity as well. These results are possible explanations for some contradicting or inconsistent literature data concerning PMMA.