Thermal analysis of paraffins as model compounds for polyethylene

Abstract

The n-paraffins C50H102, C44H90, and C26H54 were analyzed with standard and temperature-modulated differential scanning calorimetry. Crystallization and ordering from the melt to the condis phase showed practically no supercooling. These observations were confirmed with hot-stage microscopy and a melting-point apparatus. Only the organization of the C26H54 condis crystals to fully ordered crystals showed a supercooling of 4.0 K. The measurement of the apparent reversing heat capacity with a 0.05-K modulation amplitude revealed that the melting of C50H102 was completed within 1.0 K and the isotropization of C26H54 was completed within less than 0.6 K, but 62-78% of the total transitions occurred over a much narrower temperature range of 0.1 K or less. The link to polyethylene was made with fractions of the masses 15,520, 2150, and 560 Da. The 560-Da sample corresponded to C40H82 and showed also almost no supercooling, whereas the others, with folded and extended-chain crystals, supercooled by about 10 K.