Crosslinked

Crosslinked describes a material in which polymer chains are connected by bonds that extend throughout the material, forming an interconnected three-dimensional network. These connections, or crosslinks, can be covalent bonds, ionic bonds, or physical interactions, and they may arise through chemical reactions, irradiation, or organization of the constituent molecules. The resulting network restricts chain mobility, typically reducing solubility and altering mechanical and thermal properties.

Crosslinking mechanisms vary. Covalent crosslinking uses bifunctional or multifunctional agents to form durable bridges between chain segments. Chemical approaches include glutaraldehyde, carbodiimides, epoxy- or acrylate-based systems, and photoinitiated polymerization with light-activated crosslinkers. Enzymatic crosslinking employs biological catalysts such as transglutaminase. Ionic crosslinking involves multivalent ions, for example calcium ions linking alginate chains. Physical crosslinking relies on noncovalent interactions such as hydrogen bonding, hydrophobic associations, or crystallite formation; these networks can be reversible under certain conditions. Irradiation can also generate crosslinks without added chemicals.

The degree of crosslinking, or crosslink density, strongly influences properties. Higher density generally increases stiffness and thermal stability while reducing swelling and solvent uptake. Lower density yields more pliable materials with greater swelling. Real networks may contain imperfections such as loops or dangling ends, affecting performance.

Applications span polymers and biopolymers, including hydrogels for tissue engineering and drug delivery, dental resins and coatings, elastomer vulcanization, and biofabrication. Measurement approaches include gel fraction tests, equilibrium swelling to infer network mesh size, and rheological methods that assess storage and loss moduli, all used to relate structure to function in crosslinked materials.