THE EFFECTS OF END-GROUPS ON THE CRITICAL MISCIBILITY TEMPERATURES AND THERMODYNAMIC INTERACTIONS IN POLY(DIMETHYLSILOXANE) AND POLY(METHYLPHENYLSILOXANE) BLENDS

The effect of end-groups on the phase separation of polymer blends may be significant when the long chain polymers are replaced by low molar mass oligomers which have a high proportion of chemically different end-groups. This investigation is concerned with characterizing the miscibility of binary blends of linear siloxane hompolymers, in which the components have different terminal groups. The phase separation temperatures (cloud points) were measured by a light scattering technique for blends containing poly(dimethylsiloxane) and poly(methylphenylsiloxane) in various proportions. UCST type behaviour was seen in each case and the interaction energy density parameters, LAMBDA12, of the blend systems were evaluated under critical conditions. When alpha,omega-hydroxyl terminated PDMS was substituted for alpha,omega-trimethylsilyl terminated PDMS, the interaction energy density parameters had comparable values, despite the silanol groups having the potential of forming hydrogen-bonds. The results demonstrate the usefulness of the interaction energy density parameter in a Flory-Huggins treatment for evaluating the effect of end-groups on the miscibility of binary polymer blend systems.