MICROHETEROGENEITY IN MISCIBLE BLENDS OF 1,2-POLYBUTADIENE AND 1,4-POLYISOPRENE

Blends of anionically prepared narrow molecular weight distribution 1,2-polybutadiene (>99% 1,2;1,2-PBd) and polyisoprene (93 % 1,4;PI) have been studied. The molecular weights are sufficiently high that the polymers are entangled in the melt (11-50 entanglements per chain). DSC studies confirm that the polymers are miscible but the glass transition region is very broad for blends with high 1,2-PBd content. The viscoelastic properties of the blends have been studied over a wide temperature range. Individual relaxations of the components are observed. The blends are thermorheologically complex because the temperature dependence of the 1,2-PBd relaxation is stronger than that of PI. Analysis of the temperature dependence of the relaxation times suggests that each component in the blend experiences its own T(g). Isothermal relaxation times are very dependent on composition. However, iso-free volume relaxation times are not very dependent on composition, in agreement with rather small changes in the entanglement state when one polymer is diluted by the other.