Phase Morphologies and Viscoelastic Relaxation Behaviors for an LCST‐Type Polymer Blend Composed of Poly(methyl methacrylate) and Poly[(α‐methyl styrene)‐co‐acrylonitrile

Abstract

AbstractSummary: Small amplitude oscillatory shear rheology is employed to investigate the linear viscoelastic behavior of the LCST‐type PMMA/α‐MSAN polymer blends as a function of annealing temperature and time. The results reveal that when temperature approaches the separation temperature, the blends exhibit some characteristic of complex thermorheological behavior, such as a shoulder in the dynamic storage modulus G′ or the linear relaxation modulus G(t), the appearance of a loss tangent (tan δ) peak and the additional relaxation in the relaxation spectrum H(τ). All of these can be attributed to the enhanced concentration fluctuations near the phase boundary. The anomalous pretransitional behavior can be quantified to yield the binodal temperature from the inflexion of variation and the spinodal temperature on the basis of the mean field theory. Furthermore, the linear viscoelastic properties of the phase‐separated PMMA/α‐MSAN (80/20) blends can be described well by either Palierne's or Bousmina's emulsion model in virtue of the calculated $\alpha /\bar R_v$ value in the whole frequency region.Morphology images of 80/20 PMMA/α‐MSAN blends annealed for 4 h at 180 °C observed from phase contrast microscope.magnified imageMorphology images of 80/20 PMMA/α‐MSAN blends annealed for 4 h at 180 °C observed from phase contrast microscope.