The crosslinking or curing consists in linking the independent macromolecules of a polymer to build a three-dimensional structure obtained by chemical or physical means. The following figure 'Polymer-Crosslinking-Examples' schematizes three examples of the molecular arrangements of the linked macromolecules forming a 3D network:
1. Either by direct linking between two backbones
2. Or by indirect ways consisting of intermediate species, crosslinking agents, branched to two backbones
3. Or by indirect ways consisting of intermediate species, crosslinking agents, branched to pendent chemical groups (crosslinking sites).
Direct linking is often obtained by peroxides or electron beam irradiation. Crosslinking agents are a versatile and heterogeneous family including sulphur for the best known, isocyanates for polyurethanes, silane for polyethylene, resins or amines for special elastomers...This versatility expands the application field of polymers but leads to a large range of properties, each method bringing its advantages and drawbacks depending on the polymer and the used additives.