COMPATIBILIZATION OF POLYMER BLENDS BY COMPLEXATION .2. KINETICS OF INTERFACIAL MIXING

The interfacial composition and kinetics of interfacial mixing of two polymers that exhibit strong exothermic interactions, poly(N,N'-dimeth ylethylenesebacamide) (mPA) and the lithium salt of a lightly sulfonat ed polystyrene ionomer containing 7.4 mol % sulfonate groups (Li-SPS), were characterized by neutron reflectivity measurements. Blends of Li -SPS and mPA are miscible below ca. 150 degrees C as a result of the f ormation of an ion-dipole complex between the Li+-sulfonate and amide groups. Neutron reflectivity measurements were carried out on spun-coa ted bilayer films of the polyamide and a deuterated sample of the iono mer. The films were annealed at 96 degrees C, which is above the melti ng temperature of the mPA (T-m = 75 degrees C) but below the glass tra nsition temperature of the ionomer (T-g = 120 degrees C). The interfac e between the two films exhibited an asymmetric concentration profile due to the large viscosity mismatch between the two polymer, and the i nterfacial mixing followed neither Fickian nor Case II diffusion. A ki netic model that combined Fickian diffusion with a suppression of mobi lity due to intermolecular crosslinking adequately represented the exp erimental data.