Immiscibility with upper-critical solution temperature phase diagrams for poly(methyl methacrylate)/polyesters blends

Blend systems comprising poly(methyl methacrylate) (PMMA) and polyesters are classified as immiscible; however, this study has discovered that upper-critical solution temperature (UCST) behavior with partial miscibility is the more exact description for PMMA/polyester blend systems. Blends of PMMA with a series of polyesters, with structures varying in a range, were characterized in terms of phase behavior and dependence of the phase behavior on composition, temperature, and constituent's structure, and molecular weight. All PMMA/polyester blends are immiscible or only partially miscible in PMMA-rich compositions at room temperature; however, the blends can go through a phase change to miscibility at elevated temperatures. As the polyesters' structures are varied systematically (with CH₂/CO ratio from small to large), PMMA/polyester blends exhibit a trendy change in UCST phase behavior: from complete immiscibility, to complete immiscibility (in entire composition range) with UCST, then to partial miscibility (miscible in blends with PMMA contents greater than 70 wt%) with UCST, then finally back to complete immiscibility with no UCST. That is, no miscibility was found for blends of PMMA with all polyesters; however, UCST behavior, normally a rare occurrence in polymer blends, was found to be common in many of the PMMA/polyester blends investigated.