Thermoplastic materials origin, determination

The molecular origin of thermoset behavior lies in the formation of a polymeric network. Unlike thermoplastic materials, which consist of individual macromolecules that can move relative to each other over infinite distances in the melt, the polymeric chains in a thermosetting material are attached to each other and can therefore not move any more relative to each other over greater distances. They are bound together through so-called crosslinks and form an infinite, three-dimensional structure. A consequence of the presence of junctions between the polymeric chains, other than the inability to behave like a liquid and flow, is the inability of this material to dissolve in another medium such as a solvent. Solvent or plasticizer molecules can migrate into the network structure, to swell it, but this is limited to a maximum determined by the crosslink density. 

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