Step-growth polymerization, also known as condensation polymerization, involves the reaction between functional groups of monomers to form a covalent bond, resulting in the formation of a larger molecule and a small byproduct, such as water or methanol. The process continues as these larger molecules react with other monomers or other larger molecules, leading to the formation of high molecular weight polymers.In step-growth polymerization, the molecular weight of the polymer increases slowly at the beginning of the reaction and accelerates as the reaction progresses. The molecular weight distribution is generally broad, as the polymer chains can have a wide range of lengths due to the random nature of the reactions between monomers and oligomers.Chain-growth polymerization, on the other hand, involves the initiation, propagation, and termination steps. In this process, a reactive species initiator reacts with a monomer to form a reactive site, which then reacts with another monomer, adding it to the growing polymer chain. This propagation step continues, leading to the rapid formation of high molecular weight polymers.In chain-growth polymerization, the molecular weight of the polymer increases rapidly at the beginning of the reaction, and the molecular weight distribution is generally narrower compared to step-growth polymerization. This is because all polymer chains grow simultaneously, and the termination step stops the growth of the chains, resulting in a more uniform length distribution.The reaction rate in step-growth polymerization is generally slower compared to chain-growth polymerization. This is because the reaction rate depends on the concentration of functional groups, which decreases as the reaction progresses. In chain-growth polymerization, the reaction rate is determined by the concentration of the reactive species and monomers, which remain relatively constant throughout the reaction.In summary, step-growth polymerization involves the reaction between functional groups of monomers, leading to a broad molecular weight distribution and a slower reaction rate. Chain-growth polymerization involves the initiation, propagation, and termination steps, resulting in a narrower molecular weight distribution and a faster reaction rate.