Polymerization Mechanisms: A Comprehensive Review of Step-Growth and Chain-Growth Pathways

Polymerization is a fundamental process in polymer science that underpins the synthesis of materials used across diverse industrial and technological sectors. This review provides a comprehensive examination of the two principal polymerization mechanisms—step-growth and chain-growth polymerization—highlighting their distinct reaction pathways, kinetics, and structural outcomes. In step-growth polymerization, monomeric units bearing complementary functional groups combine gradually, often producing small by-products, and requiring high monomer conversion to achieve high molecular weights. Conversely, chain-growth polymerization involves the rapid addition of monomers to an active centre, enabling the formation of high molecular weight polymers early in the reaction. The review explores subtypes such as radical, anionic, cationic, and coordination polymerizations, detailing their initiation, propagation, and termination steps. Special emphasis is placed on photo polymerization as a modern approach enabling spatial and temporal control in polymer synthesis, particularly in applications like 3D printing and micro fabrication. The comparative analysis also discusses the thermodynamic and kinetic considerations, reaction conditions, and practical applications of each method. Overall, this review aims to offer a consolidated understanding of polymerization mechanisms, serving as a valuable reference for students, researchers, and professionals involved in polymer chemistry and materials science.