The postwar era saw strong emphasis on linking temperature-dependent relaxation times to processing behavior, enabling practical time-temperature superposition to predict melt flow and processing windows across wide ranges. The field moved toward a coherent thermomechanical framework where chain dynamics, entanglement effects, and crystallization are controlled by processing conditions, unifying experimental rheology with manufacturing needs. The approach also highlighted how thermal degradation kinetics and crystallization polymorphism can be harnessed to tailor properties and ensure material performance during processing. Historical Significance: This unification of thermomechanics, molecular relaxation, and crystalline control established a lasting platform for modeling and design in polymer processing, bridging laboratory insight with industrial practice. It enabled reliable scale-up, improved material performance, and informed processing routes that integrated stability, flame retardancy, and mechanical properties. The era's cross-cutting advances—time-temperature dependent relaxation, constrained chain motion, degradation kinetics, and polymorphic crystallization—became foundational pillars shaping subsequent decades of processing science and materials design.