Polycondensaation

Polycondensation is a class of polymerization in which monomers carrying two or more reactive functional groups react to form covalent bonds while releasing small molecules, such as water, methanol, or hydrogen chloride. It is typically a step-growth process, in contrast to chain-growth (addition) polymerization, in which polymer chains grow by successive addition of single monomers to active ends. In condensation polymerization, every bond formation contributes to chain growth and often to branching or crosslinking when trifunctional or higher monomers participate.

Key features include the requirement to remove the condensate (water, methanol, or HCl) to achieve high molecular weights, and the tendency for equilibrium control to limit conversion. The reaction rate and final molecular weight depend on monomer functionality, concentration, temperature, and pressure. The processes are usually carried out at elevated temperature and often under reduced pressure or with a vacuum, and may employ catalysts to accelerate ester- or amide-forming steps.

Typical condensation polymers are polyesters, polyamides, and polycarbonates. Polyesters such as polyethylene terephthalate (PET) are formed by condensation or transesterification of diacids/diols (or esters), with release of water or methanol. Polyamides (nylons) arise from diamines and diacids, producing water as a byproduct. Polycarbonates form from dihydroxy compounds and carbonyl sources such as phosgene, yielding hydrogen chloride in certain routes and involving carbonate linkages. Many other materials use similar steps to build networks or linear chains.

Applications of condensation polymers include fibers, packaging, and engineering plastics, where properties can be tailored by monomer selection and control of functionality. Environmental and processing considerations, such as hydrolytic stability and energy-intensive synthesis, influence material choices and recycling approaches.