Effects of solvent treatment on surface morphology and composition of poly(methyl methacrylate)-g-poly(ethylene oxide)

Surface morphology and composition of solution-cast films of poly(methyl methacrylate)-g-poly(ethylene oxide) (PMMA-g-PEO) were investigated by using XPS, DSC, SEM and contact angle measurement. The microphase separated structure of the copolymers was studied by TEM. Generally, for the same graft copolymer, the surface content of PEO or hydrophilicity can be as follows: Surface treated with petroleum ether or cyclohexane > surface untreated with solvent > surface treated with water or ethyl alcohol. Graft copolymer having longer PEO side chains and higher PEO content shows a separated PEO phase with even a certain degree of crystallinity on the surface. PEO crystallinity was destroyed by water or ethyl alcohol treatment; however, surface treatment with petroleum ether or cyclohexane favors the growth of PEO crystal. TEM shows that graft copolymers with longer PEO side chains (Mn of PEO, 3200) may readily undergo microphase separation and the shape and size of domains depend on the copolymer's composition.