Abstract
Dynamic viscoelastic properties of blends of poly(methyl methacrylate) (PMMA) and poly(styreneβcoβacrylonitrile) (SAN) with various AN contents were measured to evaluate the influence of SAN composition, consequently Ο parameter, upon the melt rheology. PMMA/SAN blends were miscible and exhibited a terminal flow region characterized by Newtonian flow, when the acrylonitrile (AN) content of SAN ranges from 10 to 27 wt %. Whereas, PMMA/SAN blends were immiscible and exhibited a long time relaxation, when the AN content in SAN is less than several wt % or greater than 30 wt %. Correspondingly, melt rheology of the blends was characterized by the plots of storage modulus Gβ² against loss modulus Gβ³. Log Gβ² versus log Gβ³ plots exhibited a straight line of slope 2 for the miscible blends, but did not show a straight line for the immiscible blends because of their long time relaxation mechanism. The plateau modulus, determined as the storage modulus Gβ² in the plateau zone at the frequency where tan Ξ΄ is at maximum, varied linearly with the AN content of SAN irrespective of blend miscibility. This result indicates that the additivity rule holds well for the entanglement molecular weights in miscible PMMA/SAN blends. However, the entanglement molecular weights in immiscible blends should have βapparentβ values, because the above method to determine the plateau modulus is not applicable for the immiscible blends. Effect of Ο parameter on the plateau modulus of the miscible blends could not be found. Β© 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008