Modulus and yield resistance of glassy blends containing diluents manifesting varying degrees of mobility: Polyphenylene ether/polystyrene/diluent mixtures

The glass temperatures, moduli, and yield stresses for shear failure have been characterized for homogeneous blends of poly(2,6-dimethyl-1,4-phenylene ether), homopolystyrene (1/1), and a number of diluents of T_gs from ?134 to +32°C. In a blend series based of a given diluent, the mechanical properties vary with blend T_g at rates that are characteristics of the particular diluent. These characteristic rates are found to depend strongly on the T_g of the neat diluent. Thus, for blends all with T_g = 90°C, for example, modulus and yield stress differ by as much as 50% over the range of diluents. Low-temperature relaxation measurements together with a number of previous dynamic spectroscopy studies of polymer/diluent systems at low temperatures suggest that many single-phase polymer/diluent blends may exhibit two primary relaxations—the depressed alpha relaxation of the resin and a somewhat elevated alpha relaxation of the diluent—at quite different temperatures. Both of these relaxations influence stiffness and strength properties at intermediate temperatures. The often-studied antiplasticization phenomena are viewed as a aberrations from a much more general influence of plasticizers on properties at temperatures below the alpha relaxation of the resin.