Kathy L. Singfield^1,, Ashley J. Rowe¹

This article describes a laboratory experiment used to investigate the phenomenon of multiple melting in polymers. The experiment is aimed at the level of senior undergraduate chemistry students able to carry out the investigation in a research-style approach, working together in small groups. The experiment highlights characteristic thermal behavioral differences between polymers and small organic molecules. It demonstrates that shifts in observed melting temperature upon heating are typically due to inherent metastability of the polymer system and not to impurities in the sample, for example. Differential scanning calorimetry is used to demonstrate and explore this fundamental yet contemporary subject of polymer melting, using a well-known and commercially available polymer, isotactic polystyrene. Effects of thermal history of the sample, including crystallization temperature and crystallization time, as well as analysis conditions including heating rate, on the melting point of the polymer solid are each investigated. The experiment provides a hands-on example of structure-property relationships in polymer science.

polymer, phase transitions, differential scanning calorimetry, isotactic polystyrene, multiple melting, upper-level undergraduate laboratory