Miscibility and LCST behavior of polyisoprene/poly(cis-butadiene-co-1, 2-vinylbutadiene) blends

Abstract

The miscibility of rubber blends, such as poly(cis-butadiene-co-1, 2-vinylbutadiene) (V-BR) and polyisoprene (IR), was studied with differential scanning calorimetry (DSC), torsion braid analysis (TBA) and transmission electron microscopy. The V-BR with high vinyl content above 32.3 wt% was miscible with IR, while the V-BR with lower vinyl content less than 24.3 wt% was immiscible. In regard to V-BR (32.3)/IR blends the lower critical-solution-temperature (LCST) type phase diagram was shown by means of the glass transition (Tg) behavior of annealed blends. The miscible and immiscible phase boundary would be sharp against the random copolymer content (at around 30 wt% vinyl content in V-BR). The Tg behavior of these miscible blends were in good agreement with Gordon-Taylor equation. In addition to DSC and TBA measurements the transmission electron micrographs were obtained to confirm the blend morphology in the ultra-thin sections stained with osmium tetraoxide. © 1989 The Society of Polymer Science, Japan.