Blend phase diagrams recorded with cast films

Abstract

AbstractPhase diagrams of amorphous polymer blends are discussed that are recorded using cast films. Films of all blend compositions were cast at temperatures ranging over a wide interval, using different solvents, both above and below the glass transition temperatures of the blends. Phase diagrams thereby obtained can, if there is a proper choice of solvents and conditions, show the miscibility of polymers not only in the liquid but also in the glassy state. The theory of blend film casting is analyzed using the classical Flory‐Huggins model for compatibility and the Fox‐equation for the glass transition. It turns out that miscibility is reliably determined when slightly selective solvents are used. Errors made with non‐selective and too selective solvents are estimated. The film‐casting method was tested with blends of poly(methyl methacrylate) and random copolymers of styrene and methyl methacrylate.