Semicrystalline morphology of poly(aryl ether ether ketone)/poly(ether imide) blends

A variety of semicrystalline morphologies in poly(aryl ether ether ketone)/poly(ether imide) (or PEEK/PEI) blends are revealed by electron and optical microscopy. Although the two polymeric components are compatible in the melt, phase separation occurs during crystallization of the PEEK component. At high temperatures ( approx 320 deg C), compact PEEK spherulites are observed even for dilute blends containing only 25% PEEK, and the accumulation of rejected PEI is primarily interspherulitic. At intermediate temperatures, PEI segregates primarily to pockets between bundles of lamellae within a spherulite. The length scale of segregation is progressively smaller at lower temperatures. At the lowest temperatures, approx 35 deg C above the glass transition temperature, a new and unexpected single-crystal-like dendritic morphology results. This morphology appears unique to the blends and consists of short, crystallographically faceted lamellae, uncharacteristic of typical PEEK lamellae. At all temperatures, the same unit--cell dimensions for PEEK are found.