Isothermal enthalpy studies of poly(methyl methacrylate) stereoisomers and their blends

The residual enthalpies of slow cooled atactic and isotactic poly(methyl methacrylate) were measured as a function of temperature. The samples were found to contain exothermic amorphous heats which decreased linearly with temperature below their respective Tg ’s. Blends of atactic and isotactic poly(methyl methylcrylate) were found to be one or two phase by differential scanning calorimetry depending on the method of preparation. The redisual enthalpies of the blends were lower than the pure components for the one-phase blend and a weight average of the pure components for the one-phase blend and a weight average of the pure components for the two-phase blend. Polymer-polymer heats of mixing were calculated by comparing the residual enthalpies of the blends to that of the pure components. The magnitude of the polymer-polymer heat of mixing is shown to be a measure of the extent of interaction of the blend relative to the pure components.