Rheological and thermodynamic study of the miscible blend polystyrene/poly(cyclohexyl methacrylate)

Blends of anionically prepared narrow-molecular-weight-distribution polystyrene (PS) and poly(cyclohexyl methacrylate) (PCHMA) of different molecular weights have been studied. The molecular weights of the PCHMA samples are in the range of two to three entanglement molecular weights M(e). The phase diagram was determined by turbidimetry. The critical temperature is about 245 degrees C. Differential scanning calorimetry investigations of the blends show one glass transition temperature and a width of the glass transition that give evidence of miscibility. The viscoelastic properties of the blend components and the blends have been studied in a wide range of temperatures. The investigations of the isotherms of the storage and loss moduli of the blends show that individual relaxation of the blend components is observed to a certain degree. Nevertheless, the deviations from a master curve are small, and comparison with other miscible polymer blends supports the idea that time-temperature superposition holds approximately. Material parameters like the Newtonian viscosity eta(0), the plateau modulus G(p) and the terminal relaxation time lambda(0) are determined from the material functions. These parameters follow a quadratic mixing rule for the logarithm of the material parameter rather than for the parameter itself. In analogy to Wu's equation, the mixing rule contains a material parameter m(12) that accounts for the hetero contacts between dissimilar chains. In our case, this material parameter is the viscosity eta(12), the plateau modulus G(p12) or the terminal relaxation time lambda(012), respectively. The values of these parameters support the concept of enthalpic interactions, which cause miscibility in the PS/PCHMA blend system. (C) 1996 Elsevier Science Ltd.