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

摘要

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 deg C, which is a miscible one-phase region between their lower critical solution temperature (LCST: T_c = 220 deg C; #phi#_c approx= 0.5) and T_m (approx= 120 deg C) of P(VDF-HFA), simultaneous measurements of transient tensile stress #sigma#(t) and birefringence #DELTA#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)(ident to #DELTA#n(t)/#sigma#(t)) increased monotonically with increasing volume fraction #phi#_(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))#phi#_(P(VDF-HFA)) + C_(PMMA)#phi#_(PMMA) with the suffices being relevant to each component. The value of C(t) extrapolated to #phi#_(P(VDF-HFA)) = 1 yielded C_(P(VDF-HFA)) = 6.5 * 10~(-9) Pa~(-1). The C(t) vs #phi#_(P(VDF-HFA)) 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.