Polylactides (PLAs) and related biodegradable polymers are used in medical applications and are becoming more prominent in commercial packaging materials. These practical applications make PLAs and related polymers interesting to students. The ability of PLAs to adopt either partially crystalline or amorphous arrangements depending upon their stereochemistry also make the polymers ideal candidates for analysis by differential scanning calorimetry (DSC) in an undergraduate chemistry lab. Thus, an experiment was designed to use DSC to measure the thermal properties of polymers made from lactide and glycolide. In the experiment, students explore how polymer composition and thermal history affect the melting temperature, crystallization temperature, heat of fusion, heat of crystallization, and glass transition temperature for an isotactic L-PLA, an atactic DL-PLA, and a polyglycolide (PGA). Calixarene-core PLA star polymers and a variety of commercial packaging materials containing PLA are also analyzed. Students determine percent crystallinity and innate crystallinity of a polymer by comparing commercial L-PLA with a sample of L-PLA that has been melted and rapidly cooled. They use this information in analyzing DSC data for commercial products to identify the polymer used in a product and to correlate its material properties (rigidity) with its percent crystallinity.

Measuring the thermal properties of polymers made from lactide and glycolide: An undergraduate chemistry experiment using differential scanning calorimetry

253rd National Meeting (2017)

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