page_title: Thermoset polymer matrix
section_title: Polyester resins
hierarchical_section_title: Thermoset polymer matrix / Polyester resins
caption_attribution_description: English: Unsaturated polyester resin synthetic pathway and structure
context_page_description: A thermoset polymer matrix is a synthetic polymer reinforcement first developed for structural applications, such as glass-reinforced plastic radar domes on aircraft and graphite-epoxy payload bay doors on the space shuttle. In polymer matrix composites, polymers act as binder or matrix to secure in place incorporated particulates, fibres or other reinforcements.
  They were first used after World War II, and continuing research has led to an increased range of thermoset resins, polymers or plastics, as well as engineering grade thermoplastics, all developed for use in the manufacture of polymer composites with enhanced and longer-term service capabilities. Thermoset polymer matrix technologies also find use in a wide diversity of non-structural industrial applications.
  The foremost types of thermosetting polymers used in structural composites are benzoxazine resins, bis-Maleimide resins, cyanate ester resins, epoxy resins, phenolic resins, unsaturated polyester resins, polyimides, polyurethane resins, silicones, and vinyl esters.
context_section_description: Unsaturated polyester resins are an extremely versatile, and fairly inexpensive class of thermosetting polymer formed by the polycondensation of glycol mixtures containing propylene glycol, with a dibasic acid and anhydrides usually maleic anhydride to provide backbone unsaturation needed for crosslinking, and orthophthalic anhydride, isophthalic acid or terephthalic acid where superior structural and corrosion resistance properties are required. Polyester resins are routinely diluted/dissolved in a vinyl functional monomer such as styrene and include an inhibitor to stabilize the resin for storage purposes. Polymerisation in service is initiated by free radicals generated from ionizing radiation or by the photolytic or thermal decomposition of a radical initiator. Organic peroxides, such as methyl ethyl ketone peroxide and auxiliary accelerators which promote decomposition to form radicals are combined with the resin to initiate a room temperature cure. 
  In the liquid state, unsaturated polyester resins may be processed by numerous methods, including Hand Layup, vacuum bag molding, and spray-up and compression molded Sheet Molding Compound (SMC). They can also be B-staged after application to chopped reinforcement and continuous reinforcement, to form pre-pregs. Solid molding compounds in the form of pellets or granules are also used in processes such as compression and transfer molding.
caption: Unsaturated polyester resin synthetic pathway and structure
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