Understanding Ceiling Temperature As a Predictive Design Parameter for Circular Polymers

The rise of polymeric materials marks a notable achievement of the past century, yet challenges in recycling have led to their accumulation in various environments. Efforts to address this include advancements in mechanical recycling, degradation processes, and chemical recycling techniques, particularly chemical recycling to monomer, which offers a path toward a circular economy for plastics. In this perspective, we discuss how ceiling temperature (Tc) can be used as a design parameter for circular (closed-loop recyclable) polymers and provide an overview of typical experimental approaches for deriving Tc, focusing on ΔHp and ΔSp as the key parameters for prediction. The concept of Tc is heavily embedded in the polymer literature and provides a simple but still useful way of quickly ranking different polymers in terms of their relative thermodynamic stability of polymer versus monomer states. While Tc in the bulk state as an intrinsic value is a desirable quantity, it is infeasible in many cases to measure equilibrium states in the bulk; thus, many researchers have focused on investigating Tc in solution, where there may be dependencies of Tc on the solvent, concentration, or other factors, resulting in a family of apparent Tc values at each set of conditions. We thus explore computational studies as a complement to experimental measurements of Tc. To this end, we focus here on the advantages, obstacles, and outlook of the establishment of predictive computational approaches to calculate key thermodynamic parameters related to polymer circularity, namely ΔHp, ΔSp, ΔGp, and Tc values.