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 Tgs from −134 to +32°C. In a blend series based of a given diluent, the mechanical properties vary with blend Tg at rates that are characteristics of the particular diluent. These characteristic rates are found to depend strongly on the Tg of the neat diluent. Thus, for blends all with Tg = 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.