Thermodynamic interactions in blends of polydienes

Thermodynamic interactions and phase behavior in binary blends of model mix ed microstructure polybutadienes with model 1,4-polyisoprene were studied u sing small angle neutron scattering and differential scanning calorimetry ( DSC). The microstructure of the polybutadiene ranged from 8% 1.2 (92% 1, 4) to 90% 1, 2 (10% 1, 4) units, while the polyisoprene contained 93% 1,4 and 7% 3,4 units. The blends of protonated polybutadienes (HPD) with deuterate d 1,4 polyisoprene (DPI) exhibited lower critical solution temperature (LCS T) behavior when the polybutadiene contained 38 mol % or more of 1,2 units. Below this 1.2 content of the polybutadiene, all HPB/DPI blends were found to be phase separated at all temperatures above 25 degrees C. The DSC meas urements revealed that other than a blend containing 8% 1,2-polybutadiene a nd (protonated) 1,4 polyisoprene, all other blends were single phase at roo m temperature. These results are understood in the context of previous work performed by Han and coworkers on deuterated polybutadiene-protonated poly isoprene blends.