Thermosetting polymer

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A thermosetting resin is a prepolymer in a soft solid or viscous state that changes irreversibly into an infusible, insoluble polymer network by curing.[1] Curing is induced by the action of heat or suitable radiation, often under high pressure. A cured thermosetting resin is called a thermoset or a thermosetting plastic/ polymer.


The curing process transforms the resin into a plastic or rubber by cross-linking individual chains of the polymer. The cross-linking is facilitated by energy and catalysts at chemically active sites, which may be unsaturated sites or epoxy sites, for example, linking into a rigid, three-dimensional structure. This yields molecules with a large molecular weight, resulting in a material that usually decomposes before melting. Therefore, a thermoset cannot be melted and re-shaped after it is cured. This implies that thermosets cannot be recycled for the same purpose, except as filler material.[2]

Some methods of molding thermosets are:


Thermosetting plastics are generally stronger than thermoplastic materials due to the three-dimensional network of bonds (cross-linking), and are also better suited to high-temperature applications up to the decomposition temperature. However, they are more brittle.


  • Polyester fiberglass systems: sheet molding compounds and bulk molding compounds
  • Polyurethanes: insulating foams, mattresses, coatings, adhesives, car parts, print rollers, shoe soles, flooring, synthetic fibers, etc. Polyurethane polymers are formed by combining two bi- or higher functional monomers/oligomers. This common type of thermoset material has also recently shown to have transient properties and can thus be reprocessed or recycled.[3]
  • Vulcanized rubber
  • Bakelite, a phenol-formaldehyde resin used in electrical insulators and plasticware
  • Duroplast, light but strong material, similar to Bakelite used for making car parts
  • Urea-formaldehyde foam used in plywood, particleboard and medium-density fiberboard
  • Melamine resin used on worktop surfaces[4]
  • Diallyl-phthalate (DAP) used in high temperature and mil-spec electrical connectors and other components. Usually glass filled.
  • Epoxy resin [5] used as the matrix component in many fiber reinforced plastics such as glass-reinforced plastic and graphite-reinforced plastic
  • Polyimides used in printed circuit boards and in body parts of modern aircraft
  • Cyanate esters or polycyanurates for electronics applications with need for dielectric properties and high glass temperature requirements in composites
  • Mold or mold runners (the black plastic part in integrated circuits or semiconductors)
  • Polyester resins

See also[edit]


  1. ^
  2. ^ The Open University (UK), 2000. T838 Design and Manufacture with Polymers: Introduction to Polymers, page 9. Milton Keynes: The Open University
  3. ^ Fortman, David J.; Jacob P. Brutman; Christopher J. Cramer; Marc A. Hillmyer; William R. Dichtel (2015). "Mechanically Activated, Catalyst-Free Polyhydroxyurethane Vitrimers". Journal of the American Chemical Society. doi:10.1021/jacs.5b08084. 
  4. ^ Roberto C. Dante, Diego A. Santamaría and Jesús Martín Gil (2009). "Crosslinking and thermal stability of thermosets based on novolak and melamine". Journal of Applied Polymer Science. 114 (6): 4059–4065. doi:10.1002/app.31114. 
  5. ^ Enrique Guzman; Joël Cugnoni; Thomas Gmür (2014). "Multi-factorial models of a carbon fibre/epoxy composite subjected to accelerated environmental ageing". Composite Structures. 111 (4): 179–192. doi:10.1016/j.compstruct.2013.12.028.