Interface modification in an immiscible rod-coil polymer blend using functionalized copolymers and polyelectrolytes

Abstract

Blends of rod-like and flexible-coil polymers are attractive for synthesizing molecular composites. In this study, a blend of a rod-like polymer (Vectra B950) and a flexible polymer (polystyrene) is used to investigate the influence of polymer-polymer specific interactions on interfacial properties and mechanical performance of the blend. Specifi cally, in uncompatibilized blends, the effect of vectra concentration and domain size on shear modulus is studied. While, in blends compatibilized with small amounts of poly(styrene-co-maleic anhydride) copolymer and with sodium poly(styrenesulfonate), a polyelectrolyte, we evaluate the effect of compatibilization on the dispersed phase domain size, size distribution. and blend modulus. Additionally, birefringence, dichroism, and optical microscopy measurements are used to study the effect of shear flow on blend microstructure. Our results show that while prolonged shear has little compatibilizing effect on the rod-coil blends, small amounts of copolymer and polyelectrolyte compatibilizers dramatically alter mechanical properties and blend microstructure. For both types of compatibilizers, maximum performance is observed at compatibilizer concentrations somewhat higher than the critical micelle concentration. Polyelectrolytes are found to be much more efficient compatibilizers than copolymers apparently because they form stronger bonds at the domain interface. It has also been found that the blend rheology manifests a complex interplay between macromolecular and form effects. For example, heretofore unobserved features, such as concentration dependent rninima in loss modulus versus frequency plots with no corresponding extrema or plateau in the storage modulus plots, are reported and shown to be direct consequences of this interplay between form and intrinsic effects.