Effective Morphology Control in an Immiscible Crystalline/Crystalline Blend by Artificially Selected Viscoelastic Phase Separation Pathways

We investigated the interplay between viscoelastic phase separation (VPS) and crystallization in a dynamically asymmetric crystalline/crystalline polymer blend system of poly(butylene succinate) (PBS)/poly(ethylene oxide) (PEO). The dynamic asymmetry came from the large molecular weight difference between the slow relaxing PEO and the fast relaxing PBS molecules. The evolution of network-like structures, phase inversion, and volume shrinking processes were studied by a phase contrast microscope (PCOM). The crystallization kinetics of PBS was determined by a differential scanning calorimeter (DSC). It was found that both the crystal nucleation and growth of PBS were strongly influenced by the existence and relaxation of the entangled PEO network, even though PEO was the minor component. The nuclei of PBS were more inclined to form at the interface between phase domains due to the effect of interface-assisted crystallization. Thus, the nucleation density decreased with the decrease of interfacial area. Meanwhile, the corresponding crystal growth rate was also dependent on the VPS processes. After a second quench to a temperature below the melting point of PEO, the spatial distribution of both components and the final crystallization morphology were also significantly controlled by the initial phase structures. Compared to dynamically symmetric polymer systems, the VPS process provided more versatile pathways to control the phase and crystallization morphologies in such immiscible crystalline/crystalline polymer blends.