Miscibility and phase behavior in blends of poly(vinyl butyral) and poly(methyl methacrylate)

The miscibility and phase behavior in blends of poly(vinyl butyral) (PVB) a nd atactic poly(methyl methacrylate) (PMMA) were studied by dynamical mecha nical thermal analysis (DMTA) and optical microscopy (OM). PVB is regarded as a random copolymer containing vinyl butyral (VB) and vinyl alcohol (VA) units. In this study the copolymer Composition was varied over a wide range ; and PMMA was varied with respect to molecular weight. DMTA measurements s how two distinct T-g's for the blends of all PVBs with PMMAs of high molecu lar weights (M-W = 1.2 x 10(5) and 1.5 x 10(4)), indicating completely immi scibility. However, OM observations show that the size of phase-separated d omains of PVB blends with PMMA (M-W = 1.2 x 10(5)) depends on copolymer com position and displays a minimum in the range 22-53 wt % VA content. For low molecular weight PMMAs (M-W = 2 x 10(3) to 5 x 10(3)), miscibility with UC ST-type phase behavior was observed in certain blends, the miscibility rang e depending on the copolymer composition and the molecular weight of the PM MA. The segmental interaction parameters of chi (VA), (MMA), chi (VB), MMA and chi (VA),(VB) and their temperature dependence were determined from the study. The copolymer composition dependence of the averaged interaction pa rameter between PVB and PMMA, chi (12), was then calculated and displayed a minimum around 30 wt % VA content. These finding can all be interpreted in terms of a copolymer effect in which the unfavorable interaction between P VB and PMMA is minimized at a certain copolymer compositions due to the rep ulsive interaction between VA and VB units within the PVB chains.