MISCIBILITY OF POLY(STYRENE-CO-METHYLMETHACRYLATE)S DIFFERING IN COMPOSITION

The mutual miscibility of random poly (styrene‐co‐methylmethacrylate)s with different compositions but a constant molecular weight of Mw ≅ 150,000 was studied at room temperature and at 180°C. Compatibility was analyzed with films cast from solutions with different solvents. The reliability of the analytical technique is discussed. The miscibility windows {x, yx}, which define the limits of miscibility of the blends of a given copolymer P (SxMMA1−x) with other copolymers P (SyMMA1−y), were determined for all x. The widths |x − yx| of these windows are, contrary to the predictions of the Flory–Huggins model, different for yx > x and yx > x, and depend strongly on x. Miscibility is better for blends with a high MMA content. The windows are markedly wider at room temperature. Many blends are, therefore, “semicompatible,” i.e., have a critical point of the LCST type between room temperature and 180°C. Copyright © 1990 John Wiley & Sons, Inc.