8.9 Thermosetting Resin

The term thermosetting polymer refers to a range of systems which exist initially as liquids but which，on heating，undergo a reaction to form a solid，highly crosslinked matrix. A typical example is provided by the condensation of methylol melamine to give the hard，tough，crosslinked melamine resin. Partly polymerized systems which are still capable of liquid flow are called prepolymers. Prepolymers are often preferred as starting materials in technology. In practical terms，an uncrosslinked thermoplastic material can be reformed into a different shape by heating，but a thermosetting polymer cannot.