From Controlled Reactions to the Thermal Runaway: Radical Polymerization as an Undergrad Lab Course Exercise for Enhanced Process Safety Awareness

Free radical polymerization is a common tool in industry to produce a vast array of different useful polymers. The convenient polymerization reaction known for decades is carried out industrially on a multiton scale and is also known to be very safety-critical. The self-accelerating nature of free radical polymerization demands control and careful reaction design to avoid thermal runaway. Herein, a student experiment for a practical lab course is presented, which uses free radical polymerization as a convenient model for a process safety-relevant reaction. The homopolymerization of butyl acrylate is conducted with different setups to show what happens if evaporative cooling is correctly applied, if cooling of the reaction fails, and if no evaporative cooling is applied at all. The experimental plan is versatile and can be conducted by the students themselves in a time frame of one lab day or as a shortened variation of 3-4 h. If necessary, the experiment can also be prepared in advance by a supervisor and shown to a classroom in approximately 1 h. The costs for the needed chemicals and solvents are very low, and the equipment needed can be varied from a standard preparative organic chemistry setup to online digital temperature recording and monitoring. The described polymerization of butyl acrylate is a model system to teach the concept of reaction heat and evaporative cooling, shows the usefulness of reaction calorimetry, and improves the awareness of process safety and critical thinking during the design of new experiments.