Effect of Partial Saturation on Thermodynamic Interactions in Polydiene/Polyolefin Blends

Polymer blends exhibit properties that are highly dependent on interactions between components, typically quantified by the Flory-Huggins interaction parameter, χ. Prediction of blend phase behavior requires characterization of the temperature dependence of χ. Polyolefins and polydienes are important materials with commercial relevance as elastomers. The majority of previous studies on the thermodynamics in polyolefin and polydiene systems have focused on polymer pairs within the same class (i.e. polyolefin/polyolefin and polydiene/polydiene blends), which generally exhibit a small and weakly temperature dependent χ. There is little quantitative information on thermodynamic interactions in systems that contain both polydienes and polyolefins. In our previous work, we characterized the χ parameter in a model polydiene/polyolefin blend based on 1,2-polybutadiene (1,2-PBD) by small angle neutron scattering (SANS). 1,2-PBD was chosen as a model system as it is amorphous, allowing for characterization of χ over wide temperature range, and can be synthesized through anionic polymerization with low dispersity and high 1,2 content (>99%). SANS data were analyzed through Random Phase Approximation and Zimm analyses in order to extract χ as a function of temperature. We observed an unusually large χ parameter in blends of 1,2-PBD and saturated 1,2-PBD that exhibited a strong temperature dependence. This feature enables facile control over phase behavior during processing at elevated temperatures. We also studied the impact of partial saturation on the thermodynamics of polydiene/polyolefin blends. The χ(T) behavior in blends of fully saturated (with deuterium) 1,2-PBD with partially saturated (with hydrogen) 1,2-PBD, at varying levels of saturation (covering the full range from 0-100%), was characterized. The applicability of the random copolymer theory to predict χ(T) behavior in these blends was evaluated.