The free-radical retrograde-precipitation polymerization (or FRRPP) process is a free-radical-based chain polymerization process that occurs above a lower critical solution temperature (LCST). The unique features of FRRPP have been exploited for the synthesis of novel amphiphilic materials under industrially practicable conditions. In the work described here, the copolymerization of styrene and acrylic acid via FRRPP is modeled and simulated to derive greater understanding behind the polymerization mechanism. The penultimate model is used to calculate the reactivity ratios. These reactivity ratios are used to calculate conversion, composition, and molecular weight distributions using the mole balance equations for the different species in the system and the Achilias Kiparissides model for the calculation of reaction rate coefficients. The results suggest that precipitation and the resulting phase separation and change in diffusivities have a strong impact on the polymerization kinetics. The penultimate model provides a better representation of the reactivities, in comparison to other approaches.