Polymer physical gels composed of poly(vinylidene fluoride) (PVDF) and propylene carbonate with networks of interconnected spherulites were thermally annealed near peak melting temperature (T-m). Although the gels prepared at high gelation temperature showed the brittle mechanical properties, the gels annealed near Tm were simultaneously stiffened, strengthened and toughened in addition to increase in T-m. By in-situ Hv light scattering, it was found that recrystallization was highly enhanced during the cooling process after annealing while partial melting of small crystallites of PVDF occurred at around annealing temperature near T-m during heating process and recrystallization proceeded over the thermal treatment. Since growth of the spherulites was also found to proceed during heating and annealing processes, the strengthened interspherulitic boundaries obtained by SEM were ascribed to the growth of the spherulites during the heating and annealing processes and the enhanced recrystallization during the subsequent cooling process. Crystalline phase of PVDF was revealed to transform from the dominant beta phase to the dominant g phase during the annealing process by WAXS and FT-IR/ATR measurements, which in part contributed to the increase in T-m. Fracture surface images obtained by SEM and in-situ digital microscope images during stretching of the annealed gels revealed that the spherulites with both the increased crystallinity and the strengthened boundaries could be deformed uniaxially in the stretching direction without morphological transformation into fibrils. Based on the results of the hierarchical structure characterizations, not only increase in crystallinity but also formation of the strengthened interspherulitic boundaries is the possible origin of the significant improvement of the mechanical properties of the gels annealed near T-m. (c) 2018 Elsevier Ltd. All rights reserved.