Polymer materials are the core components of many daily necessities, such as heating pads and heat-sealing films. Unlike ice and pure metals that melt instantly at a fixed temperature, polymers require a temperature range to fully melt, a phenomenon rooted in their unique crystal structure.
    Pure crystals like metals have regular lattices without defects, so they melt at a constant temperature, showing sharp and symmetric peaks in DSC curves. In contrast, polymers are ultra-long chain molecules, and their crystals are "mixed lamellae with inconsistent sizes" – featuring uneven thicknesses, various defects, and molecular chains of different lengths. According to the Gibbs-Thomson equation, crystal thickness and defect level affect melting points. When heated, crystals with different stabilities melt sequentially, forming broad DSC peaks and macroscopically presenting as melting ranges.
    This characteristic is crucial for industrial production: polypropylene (PP) with a wide melting range (20~40℃) is easy to process for beginners, while polybutylene terephthalate (PBT) with a narrow range (5~10℃) requires precise temperature control. Material performance can be optimized by adjusting molecular weight distribution and crystallization history. Understanding this principle helps us better apply polymer materials.

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