Component Dynamics in Miscible Blends of 1,4-Polyisoprene and 1,2-Polybutadiene

The effects of blending on the rheology of the individual components in highly entangled miscible blends of 1,4-polyisoprene (PI) and 1,2-polybutadiene (1,2-PB) are investigated. Blend component contributions to the dynamic modulus, G*(ω), are recovered over the full composition range by complementing dynamic mechanical rheometry with infrared polarimetry. Distinct relaxations for each component are observed. Analysis of the modulus amplitudes of the component G*(ω) contributions reveals that the behavior of the slower relaxing component, 1,2-PB, compares well with constraint release scaling predictions. Each component is found to have a different average number of skeletal bonds between entanglements, in agreement with the predictions of an existing entanglement theory. The components appear to adopt a single reptation tube diameter and a mutual modulus shift factor, b_T(T), in each blend. Analysis of the frequency dependence of the component G*(ω) contributions indicates that each component's relaxation is governed by a distinct apparent glass transition temperature, T_g, and that at a constant T -T_g blend composition only mildly influences the component relaxation times. A mild increase in the 1,2-PB relaxation time in the blend suggests a possible increase in the 1,2-PB friction factor in the presence of PI.