Cross-link

A cross-link is a covalent bond or physical association that joins separate polymer chains, limiting their independent motion and changing the material’s properties.

Covalent bond: A chemical bond formed when atoms share electron pairs. Covalent cross-links permanently join polymer chains through shared-electron bonds.
Hydrogel: A water-swollen polymer network that retains its structure through physical or chemical links. Cross-links keep the water-rich polymer matrix from dissolving.
Polymer: A substance composed of large molecules built from repeating or related molecular units. Cross-links connect the macromolecules that make up polymer materials.
Polymer entanglement: A topological interweaving of polymer chains that restricts motion without permanent chemical bonds. Entanglements constrain chains like cross-links but can relax as chains move.
Hydrogen bond: An attraction involving hydrogen bonded to an electronegative atom and another electronegative atom. Hydrogen bonds can create reversible physical links between polymer chains.
Thermosetting polymer: A polymer that cures into a permanently networked structure and cannot be remelted. Its extensive cross-linking gives it shape stability after curing.
Polymer chain: A long macromolecule whose atoms or molecular groups form a connected sequence. A cross-link joins distinct chains rather than extending just one chain.
Chain scission: The breaking of a polymer backbone into shorter molecular chains. Scission severs chains, whereas cross-linking joins separate chains.
Vulcanization: A process that strengthens rubber by forming cross-links, commonly with sulfur. It is a familiar chemical route for cross-linking elastomer chains.
Elastomer: A polymer material that can undergo large reversible deformations. Sparse cross-links help stretched chains return toward their original configuration.

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