AN EXPERIMENTAL-STUDY OF THE THERMODYNAMIC PROPERTIES OF MULTICOMPONENT POLYOLEFIN BLENDS WITH ORDERED AND DISORDERED PHASES

Concentration fluctuations and phase transitions in multicomponent pol ymer blends comprising polyethylene (PE), head-to-head polypropylene ( PP), and a symmetric PE-PP diblock copolymer were studied by a combina tion of light and neutron scattering. When block copolymer concentrati on was below a certain threshold (12.5 vol % in our system), the blend s exhibited macrophase separation. At higher block copolymer concentra tions, we found stable, periodic structures that were characterized by a neutron scattering peak at finite scattering vector, q. In this reg ime, the block copolymer serves as a surfactant. At high block copolym er concentrations, ordered microphases that were similar to those foun d in pure block copolymer melts were obtained. At lower block copolyme r concentrations, however, microemulsions that are periodic phases tha t lack long-range order were obtained. Concentration fluctuations of i ndividual components in these multicomponent mixtures in the single-ph ase regime were examined by conducting neutron scattering experiments on contrast-matched systems. The formation of disordered phases and mi croemulsions is announced by transient intermolecular aggregation of t he homopolymers. In contrast, the formation of ordered structures is a nnounced by both intermolecular and intramolecular signatures. Many of our results are in quantitative agreement with theoretical prediction s based on the random phase approximation.