(50b) Morphology and Rheology of Model Immiscible Blends with Interfacial Crosslinking

Reactive compatibilization ? generating a compatibilizer by an interfacial chemical reaction between polymers in different phases ? is a well-established method in the polymer blend industry. Typically, an end-functional polymer such as polyamide in one phase reacts with a multifunctional polymer such as a maleated polyolefin in the other phase to form a graft copolymer. In this paper we explore immiscible polymer blends in which both reactive species are multifunctional, and thus form a crosslinked network at the interface.

We compare two model blends, a ?reference? blend compatibilized by a diblock copolymer, and a reactive blend compatibilized by an interfacial crosslinked network. Optical microscopy shows that the diblock-containing blend forms a typical droplet matrix morphology. In contrast, the reactive blend shows a droplet-matrix morphology with non-spherical drops, sometimes with wrinkled interfaces. Interestingly, the drops of the reactive blend are joined together in a space-spanning network. All these features are attributable to the interfacial crosslinking in the reactive blend.

The rheological properties (creep, recovery, and dynamic oscillatory) of the diblock-containing blend are similar to those of compatibilized droplet-matrix blends studied previously. At adequately high compatibilizer concentrations, the reactive blend exhibits gel-like behavior and coalescence of the dispersed phase drops is suppressed. Upon shearing, the reactive blends show a large viscosity and creep recovery at short shearing times suggesting a breakdown of the network structure upon shearing. These non-Newtonian properties strongly increase with increasing compatibilizer concentration. At lower compatibilizer concentrations, the rheological properties of the reactive blend are similar to uncompatibilized blends studied previously. Varying the volume fraction results in a sharp increase in the viscosity and creep recovery near the phase inversion point. Interestingly, when PDMS is the majority phase no gel-like behavior is observed, even at high compatibilizer concentrations.

A significant risk when dealing with multifunctional reactive systems is the possibility of crosslinking the entire bulk and rendering the material an unprocessable solid. Notably in the present case, the steady shear viscosity of the reactive blend remains comparable to that of the diblock blend. This suggests that in spite of the crosslinked nature of the compatibilizer, because the crosslinking is restricted to the interface of the drops, the reactive blend remains processable.