Polyester resin

Maleic anhydride is a commonly used raw material with diacid functionality in unsaturated polyester resins.

[5][6] Unsaturated polyesters are condensation polymers formed by the reaction of polyols (also known as polyhydric alcohols), organic compounds with multiple alcohol or hydroxy functional groups, with unsaturated and in some cases saturated dibasic acids.

Maleic anhydride and styrene are known to form alternating copolymers, and are in fact the textbook case of this phenomenon.

Transition metal salts are usually added as a catalyst for the chain-growth crosslinking reaction, and in the industry this type of additive is known as a promoter; the promoter is generally understood to lower the bond dissociation energy of the radical initiator.

Unsaturated polyesters (UPR) are utilized in many different industrially relevant markets, but in general are used as the matrix material for various types of composites.

UPRs are also used in non-reinforced applications with common examples being gel coats, shirt buttons, mine-bolts, bowling ball cores, polymer concrete, and engineered stone/cultured marble.

The most common and highest volume produced polyester is Polyethylene terephthalate (PET), which is an example of a saturated polyester and finds utilization in such applications as fibers for clothing and carpet, food and liquid containers (such as a water/soda bottles), as well as films.

When curing a UPR, the fumarate form is known to react more rapidly with the styrene radical, so isomerization catalysts, such as N,N-dimethylacetoacetamide (DMAA), are often employed in the synthesis process which converts the maleates into fumarates; the isomerization can also be encouraged with increased reaction time and temperature.

Within the UPR industry, the classification of the resins is generally based on the primary saturated acid.

In one process, the DCPD is cracked in situ to form cyclopentadiene which can then be reacted with maleate/fumarate groups along the polymer chain via a Diels-alder reaction.

FRP composites utilizing ortho resins are found in such application as boat hulls, bath ware, and bowling ball cores.

The end product is functionally the same as a Tere resin, but can often be lower cost to manufacture as scrap PET can be sourced cheaply.

[12] Lichens have been shown to deteriorate polyester resins, as can be seen in archaeological sites in the Roman city of Baelo Claudia Spain.