Polymercrosslinking

Polymercrosslinking is the process by which polymer chains are interconnected through multifunctional bonds to form a three-dimensional network. The resulting materials are typically insoluble and exhibit enhanced mechanical and thermal properties; their performance is largely determined by crosslink density, functionality, and the uniformity of the network.

Covalent crosslinking uses covalent bonds to create permanent networks. Common routes include epoxy-amine, ester/urethane linkages formed by condensation or step-growth polymerization, radical polymerization with difunctional monomers, and "click" reactions such as azide–alkyne cycloaddition. Thermal curing, UV or visible light initiated photoinitiation, and chemical crosslinking agents (for example glutaraldehyde or carbodiimides) are typical processing methods.

Physical crosslinking relies on non-covalent interactions or reversible bonds. Examples include ionic crosslinks (for instance alginate with divalent cations), hydrogen bonding, metal–ligand coordination, and crystallite formation in some polymers. These networks can be reversible, enabling self-healing, reshaping, or remodeling in response to stimuli.

Crosslink density and functionality determine modulus, swelling, permeability, and glass transition behavior. The gel point marks the onset of network formation, and models such as Flory–Stockmayer or Flory–Rehner describe network formation and swelling. Heterogeneities and residual reactive sites influence properties and aging.

Applications span hydrogels for tissue engineering and drug delivery, elastomeric rubbers and coatings, membranes for separation, adhesives, and shape-memory or responsive materials. Safety and environmental concerns emphasize selecting biocompatible and low-toxicity crosslinkers where appropriate and controlling unreacted residues during processing.