Elongational flow birefringence of poly(methyl methacrylate)/poly(vinylidene fluoride-co-hexafluoro acetone) blends

Abstract

For blends of a poly(methyl methacrylate) (PMMA) and a poly(vinylidene fluoride-co-hexafluoro acetone) [P(VDF-HFA)], we examined phase behavior and crystalline melting ( T m) and glass transition ( T g) temperatures. In the range 130–160°C, which is a miscible one-phase region between their lower critical solution temperature (LCST: T c=220°C; φ c≅0.5) and T m (≅120°C) of P(VDF-HFA), simultaneous measurements of transient tensile stress σ(t) and birefringence Δ n( t) were conducted via elongational flow opto-rheometry (EFOR) on the blends under uniaxial elongation at constant Hencky strain rates. The stress optical coefficient C(t)(≡Δ n(t)/σ (t)) increased monotonically with increasing volume fraction φ P(VDF-HFA) of P(VDF-HFA) in the blend. Molten PMMA/P(VDF-HFA) blends in the one-phase region appear to follow the stress optical rule with C(t) obeying the simple additivity: C(t)= C P(VDF-HFA)φ P(VDF-HFA)+C PMMAφ PMMA with the suffices being relevant to each component. The value of C(t) extrapolated to φ P(VDF-HFA)=1 yielded C P(VDF-HFA)=6.5×10 −9 Pa −1. The C(t) vs φ P(VDF-NFA) behavior suggested that C(t) can be zero for the (97/3) blend or the addition of only 3% P(VDF-HFA) to PMMA makes the blend non-birefringent. Thus, P(VDF-HFA) can be an optimal modifier when PMMA is used as a high-technology optical material, e.g., optical discs and lenses.