Evolution of Condensed Structural and Mechanical Behavior in High-Viscosity Amorphous/Semicrystalline PPESK/PEKK Blends

With the advancement of research on thermoplastic high-performance engineering plastics, molecular chain structures have become increasingly intricate, leading to remarkable improvements in heat resistance. However, escalating processing challenges have hindered the widespread adoption of these materials. Blending modification emerges as the most promising approach, offering opportunities to optimize processing characteristics while enabling comprehensive performance tailoring. This study investigates the poly(phthalazinone ether sulfone ketone) PPESK/poly(ether–ketone–ketone) PEKK blend system featuring high processing temperatures, high melt viscosity, rigid molecular chains, and coexisting crystalline–amorphous phases. By integrating experimental investigations with molecular dynamics simulations, we systematically elucidate the impact of PPESK’s “twisted noncoplanar configuration” on microstructural evolution and propose a “rigid mechanical entanglement random coil” model. The mechanisms governing phase separation and crystallization in the molten blend are deciphered, revealing a composition-dependent morphological transition from “island” to “bicontinuous” phases. Notably, crystalline structures associated with enhanced thermal resistance were identified at phase interfaces, corresponding to the growth dynamics of the (2,0,0) crystallographic plane. Furthermore, the structure–property correlations among polymer ratios, interfacial compatibility, crystallinity, and macroscopic mechanical performance were quantitatively established.