Theoretical understanding of interfacial polycondensation reactions - a review

Interfacial polycondensation (IP) is a versatile route to fabricate polymers and polymer-based structures under mild conditions, enabling applications ranging from microencapsulation to ultrathin films, hollow nanospheres, and nanofibers. Despite its widespread use, the mechanistic understanding of IP remains incomplete due to the involvement of and interaction among several physicochemical processes. Over the years, several experimental methods for studying this process have evolved, as have models, which have progressed from diffusion-controlled descriptions to more sophisticated diffusion-reaction frameworks and molecular-level simulations. Yet, most approaches rely on strong simplifying assumptions, limiting their predictive power and general applicability. This review surveys the theoretical and computational studies of IP, beginning with experimental strategies to probe the fast reaction kinetics and the inherent challenges they present. We highlight early modeling approaches based on film thickness and diffusion, as well as recent advances that account for monomer dissociation, transport through growing films, reaction localization, and kinetic regimes. Concepts of polymer solution thermodynamics and nonlinear reaction theories - largely overlooked in existing IP models - are examined for their potential to explain molecular weight distribution, crystallinity, and gel/sol fractions in the resulting polymers. We also discuss molecular-scale studies employing aggregation models and dissipative particle dynamics, noting the opportunities and limitations of current simulation strategies. By integrating insights across experimental, theoretical, and computational domains, this review identifies key gaps and emerging directions for predictive modeling of IP. Bridging these scales will be essential to advance the design of functional soft materials via interfacial polycondensation.