While our understanding of irreversible copolymerization is robust and the existence of simple and validated tools for the extraction of reactivity ratios allows for rapid and accurate characterization of experimental data, such methods become inapplicable when one or both comonomers exhibit reversible propagation reactions, otherwise known as equilibrium polymerization. Equilibrium polymerization is understood through the lens of the thermodynamics of a homopolymerization reaction, i.e., a monomer homopolymerizes when such homopolymerization is thermodynamically favorable. The concentration at which polymerization becomes energetically neutral is known as the equilibrium concentration, [𝑀] /0 , which is defined at a given temperature, T, to be: