(715b) Morphological Control of Cocontinuous Polymer Blends Via Interfacial Reaction

Cocontinuous blends are microstructured polymers formed by melt processing of immiscible polymers to create two continuous interpenetrating phases.  Solvent extraction of one phase yields a porous material, which can be applied in battery separators and membrane supports.

 Blends of polyethylene (PE) and polyethylene oxide (PEO) of varying molecular weight and degrees of reactive functionality were prepared in a batch microcompounder and continuously in a pilot scale co-rotating twin-screw extruder.  The structures were stabilized by reacting hydroxyl or amine terminated PEO with maleic-anhydride functional PE to create a graft copolymer at the blend interface.  The interfacial coverage of different molecular weights of PEO on maleic-anhydride functional PE was compared by X-ray photoelectron spectroscopy, contact angle measurements, and droplet blend rheology using the Palierne viscoelastic droplet model. Varying length and functionality of PEO chains allowed us to isolate the effect of diffusion and reaction rate on the interfacial coverage of graft copolymers and consequently blend morphology. The morphology and phase size of the blends was examined using SEM (scanning electron microscopy) and LSCM (laser scanning confocal microscopy). Higher PEO interfacial coverage stabilized the interface and reduced the interfacial tension in the blends, which resulted in a smaller characteristic phase size. 

The lower molecular weight polymers showed difficulty in achieving a cocontinuous morphology, preferring to arrange into dense droplet dispersions.  A positive correlation was determined between high melt elasticity and extensional viscosity and the formation of a cocontinuous morphology.  This is due to the ability to stretch droplets of one phase into elongated structures that then intersect and form a continuous network.