polymer materials by differential scanning calorimetry (DSC) and in situ X-ray measurements. Furthermore, by combining the results of these thermal measurements with real space observations using an electron microscope, we clarified the correlation between thermal behavior and structure/property in polymer materials. We discussed the phase transition behavior from the orthorhombic phase into the hexagonal phase during heating of melt- drawn ultrahighmolecular- weight polyethylene (UHMW-PE) samples with different molecular weight characteristics, and revealed that the perfection of the phase transition and the width of the temperature window of the hexagonal phase during heating of melt-drawn UHMW-PE samples depend on their higher-order structure reflecting molecular weight characteristics. The melting behavior of polyethylene/polystyrene diblock copolymer (PE-b-PS) isothermally crystallized at different crystallization temperatures (Tc) was investigated. DSC melting thermograms for PE-b-PS isothermally crystallized at different Tcs were measured, and a deconvolution analysis was performed. The deconvolution analysis of DSC profiles was useful for evaluating the constitution of crystalline domains in the bicontinuous crystalline/amorphous structure of isothermally crystallized PE-b-PS.