Preparation and Compatibilizing Properties of Poly(styrene-graft-ethylene oxide) in Polymer Blends

One of the main trends in the polymer industry today is the increasing importance of polymer blends. Combining two or more immiscible polymers in a polymer blend often leads to multi-phase materials with desirable properties. The typical poor morphological stability and low interfacial adhesion in these blends can be eliminated by adding compatibilizing graft copolymers.

Well-defined graft copolymers, having polystyrene (PS) backbones and poly(ethylene oxide) (PEO) grafts, were prepared by anionic polymerization of EO from active sites on PS copolymers. The graft copolymers were added as compatibilizing agents to PS blends containing a dispersed phase of either poly(butyl acrylate) (PBA), poly(butyl acrylate-co-acrylic acid) (PBAAA), polyamide-6 (PA-6) or polyamide-12 (PA-12).

The graft copolymers had no compatibilizing effect in the PS/PBA blends. In contrast, the graft copolymer stabilized the morphology and significantly reduced the phase size in PS/PBAAA blends, where the PEO grafts were found to interact with the PBAAA phase via hydrogen bonds. The graft copolymers also reduced the phase size in PS/PA blends, and graft copolymer interphases between the PS and PA-6 phases were observed. Above a saturation concentration of graft copolymer, there were no further reductions of phase sizes in the blends. At these concentrations, excess graft copolymer phase separated into macrodomains. Additions of graft copolymer also increased the interfacial adhesion in the blends. One of the main conclusions gained from this work is the importance of adding appropriate amounts of compatibilizer to immiscible blends.