repolymerization

Repolymerization is the process of forming polymer chains again by linking monomer units, or by reassembling degraded polymer fragments after an initial polymerization or subsequent decomposition. It is a concept used in polymer science and waste management, often in the context of recycling or repairing polymer materials.

In chemical recycling, plastics are broken down (depolymerized) to monomers or oligomers and then purified and repolymerized to produce new polymers. This can preserve material properties and reduce demand for virgin monomers. Common pathways include hydrolysis or transesterification of polyesters like PET to generate terephthalic acid and ethylene glycol or BHET, followed by polymerization to PET again. Polystyrene can be depolymerized to styrene monomers that are subsequently repolymerized. Other polymers such as polyurethanes and polycarbonates may be depolymerized and then repolymerized, depending on process design and purity.

Methods and principles involve depolymerization techniques such as hydrolysis, glycolysis, methanolysis, and aminolysis, often coupled with purification. The repolymerization step typically uses polycondensation, step-growth, or addition polymerization, controlled to achieve desired molecular weight and properties. In some systems, reversible covalent chemistries enable dynamic repolymerization, allowing repair or reshaping of networks without complete depolymerization.

Challenges and scope include the influence of impurity, additives, and processing history on repolymerization efficiency, as well as energy requirements. While repolymerization supports circular economy goals, not all plastics are easily repolymerized to high-quality polymers, and recycling streams often require sorting and cleaning.