Thermosetting Polymers – Types and Applications

Thermosetting polymers are the group of polymers that form cross-linked structures when they solidify with the application of UV light. Because of these cross-linked structures, they can not re-melt like thermoplastic polymers. Here, you can find the most common thermosetting polymer applications.

Most Common Thermosetting Polymers

Here, you can find information about the most common thermosetting materials. Also, as their properties and applications areas.

Thermosetting Polyester

Polyester is a polymer material that can be both thermoplastic and thermosetting. It depends on the processes that they apply to polyesters. Here, we explain thermosetting polyesters and their applications and properties. Also, you can find information about unsaturated polyesters.

As we stated in thermoplastic polyester content, polyesters contain ester linkages which give the property that polyesters can be both thermosetting and thermoplastic. The starting polymer of thermosetting polyesters reaction of acids or anhydrides with glycol. The most known chemical reaction like that occurs between maleic anhydride(C4H2O3) and ethylene glycol(C2H6O2). With this chemical reaction, they produce unsaturated polyester. They mix this unsaturated polyester with a monomer that starts the cross-linking process in polyester. But a phenomenon called pre-mature cross-linking in polyesters that we must prevent with such an inhibitor addition.

Some applications that thermoset polyesters we use in;

  • We use thermosetting polyesters in large constructive items such as pipes and tanks.
  • Also, such applications as boat hulls and automotive body parts are the main applications of thermosetting polyesters.

We must make curing of thermosetting polyesters in the process of molding. After the molding process, we must make curing to obtain a cross-linked structure. We make this curing with heat application or by the addition of curing catalysts.

Properties Of Unsaturated Polyester

Unsaturated polyester molecule.
Unsaturated polyester molecule.

As we stated above, we produce unsaturated polyester with maleic anhydride, ethylene glycol, and styrene. We use styrene for preventing pre-mature cross-linking. Unsaturated polyester is a brittle material that has elongation according to its original shape 0%. We produce unsaturated polyester with a step polymerization process. Has tensile strength of 30 MPa and a modulus of elasticity of 7000 MPa.

Thermoset Silicones

As you know that silicones are very versatile materials, and we can use them in various kinds of applications because of their chemical structure and different properties. They are very important materials. Here, we will explain what are the properties and applications of elastomer silicones here.

Thermoset silicone.
Silicone dough.

Like in some plastic materials, the degree of cross-linking defines the state of silicones whether they are thermoplastic or elastomer. If there is no cross-linking, silicones will be thermoplastic material. A slight cross-linked structure at the molecular level of silicones will make them elastomeric.

The most important characteristic of elastomer silicones is the wide service temperature range. But the resistance to the effects of oils is low. Elastomer silicones can have various chemicals inside them as ‘polydimethylsiloxane’ to obtain specific properties.

Enhancement of mechanical properties is also very important for elastomer silicones. We make silica powder addition generally in the production phase of elastomer silicones to obtain reinfırced material.

They are high in cost and used in applications such as gaskets, seals, wires, and cable insulations. Prosthetic devices and caulking are also important application areas for elastomer silicones.

Properties of Silicone Rubber

The general representation of silicone rubbers in the market is ‘VMQ’. Failure elongation of silicone rubber according to its original shape is around 700%. The service temperature range is between -50C and 230C. The tensile strength of silicone rubber is around 10 MPa.

Thermoset Polyurethane

Polyurethanes are a very important polymer that we can find as thermoplastics, thermosetting, and elastomers. Here, we will discuss thermoset polyurethanes and their applications and properties.

Polyurethanes are very complex structures and we can not contain a specific group in polymers. The common thing around polyurethanes is the urethane group that they are including. The chemical representation of the urethane group is NHCOO. The reaction of polyols that contains branches of -OH groups that butylene ether glycol(C4H10O2) with isocyanate such as diphenylmethane diisocyanate (C15H10O2N2) is an example of the production of polyurethanes.

Thermosetting and elastomeric polyurethanes are the most important groups. We use polyurethanes as foams in applications generally, and this foam structure can be ranging from rigid to elastic. Some of the applications that we use polyurethane foams;

  • We use rigid foams in refrigerator walls as a thermal insulators. Also, it gives very good structural stability to refrigerator itself.
  • Also, we make some varnishing and coating processes with polyurethane foams.

Properties of Polyurethane

Polyurethane thermosets.
Polyurethane chemical representation.

Here, we will give information about polyurethane that we synthesize from the reaction of a polyol and isocyanate. The general production method is step polymerization. Elongation characteristics depend on the cross-linking that we produce in production steps. Also, the modulus of elasticity depends on the process that thermoplastics and they produce thermosetting or elastomer polyurethane. The tensile strength of polyurethane is around 30 MPa.

Thermoset Silicone Resin

We know silicones from lots of applications in engineering and daily life. Silicones also have very specific properties. Here, we will explain the general properties of thermoset silicones and some of their applications of them. Also, you can find information about thermoset silicon resins here.

Thermosetting silicone resin.
Thermoset silicone resin application.

Silicones can be semi-organic and inorganic according to the presence of siloxane links which have a chemical representation of –Si–O–. In general silicones, we combine CH3 and SiO to obtain various proportions. According to this variation, we can produce them as thermosets, elastomers, and fluids.

Silicones’ heat resistance and water resistance properties are very important for such applications. But mechanical properties of silicones such as strength are not good as other cross-linked thermosetting.

As you understand that thermosetting silicones have cross-linked molecular structures. With this highly cross-linked structure, we use them in these kinds of applications; varnishing, painting, and other coating applications for circuit boards. Curing takes place by heating the silicones.

Properties of a Silicone Thermosetting Resin

The production method of general thermoset silicones is step polymerization. They are highly brittle materials that have elongation according to the original shape is 0. Tensile strength is generally 30 MPa.

Thermosetting silicones do not have a very big market in the polymer industry. So we can summarize the general properties and applications of thermosetting silicone resins as above.

Thermoset Polyimides

Polyimides are another type of polymers that are avaliable as both thermoplastic and thermosetting. But the thermosetting polyimides are much more important because of their properties. Here, we explain these properties of polyimides and their applciations of them. Also, you can find properties of a specific kind of polyimide polymer.

Thermoset electronic wirings.
Polyimides in electrical wirings.

Thermosetting polyimides are renowned for their excellent thermal and chemical resistance properties. Because of that, they are much more important than thermoplastic ones. In the market, thermosetting polyimides have commercial names such as Kapton and Kaptrex. Because of these characteristic properties, polyimides are used in such applications as below;

  • Polyimides are widely used in insulating films.
  • Flexible cable coating application is also an important application of polyimides. Because electrical resistance is also very important for them.
  • Protective clothes and medical tubes are also other important applications of polyimides, because of their high chemical resistance.

Properties of Polyimide Thermoset Material

Polimide chemical expression.

This material constitutes chemicals that; pyromellitic dianhydride (C6H2(C2O3)2) and 4,40-oxydianiline (O(C6H4NH2)2). These starting materials are mixed in the condensation polymerization process to obtain a polyimide thermoset. Polyimides have a bigger elongation value compared with other thermosets which are 5% according to the original shape. It is very high around average thermoset values, but it can be called a brittle material. The tensile strength of this polyimide material is around 80 MPa and the modulus of elasticity of this polyimide material is around 3200 MPa.

Phenolic Thermosets

Phenolics are a type of thermosetting polymers that has specific properties. Because of these specific properties, phenolics are used in various application areas. Here, we explained these application areas of phenolics and some of the properties of phenolics. Also, you can find numeric information about phenol formaldehyde thermoset.

Phenol formaldehyde.
Phenol formaldehyde resin granules.

The source chemical of phenolics is phenol. Phenols have chemical structures of C6H5OH and can be reacted with aldehydes which are dehydrogenated alcohols. Of these alcohols, formaldehyde is the most reactive one. Because of that phenol formaldehyde is the most important phenolic thermoset.

Phenolics have a brittle structure which is also a general characteristic of thermoset materials. They have very good thermal and chemical stability. Some of the applications that phenolics and phenol formaldehyde are;

  • Phenol formaldehyde can be used on brakes and abrasive wheels as the bonding material.
  • Printed circuit boards are also a very important application area for phenol formaldehyde.
  • they are also used as adhesives for plywood.

In the production process of phenol formaldehyde, some fillers must be used. The general fillers are used for phenolics some minerals, wood flour, and cellulose fibers.

General Properties of Phenol Formaldehyde

Molecular structure of the phenol formaldehyde.
Phenol formaldehyde mulecular structıre.

Constituent chemicals for phenol formaldehyde are phenol and formaldehyde. These two have chemical formulae of C6H5OH and CH2O respectively. Because of their brittle behavior, they have a very low elongation value according to their original shape which is >1%. The tensile strength of phenol formaldehyde is around 70 MPa and the modulus of elasticity is around 7000 MPa. The production method of phenol formaldehyde is a step polymerization process.


Epoxies are one of the most important and prominent thermoset polymers because of their specific features. Because of these features, epoxies find very important application areas in engineering. Here, we explain these properties and applications of epoxies and give information about an epoxy material called epichlorohydrin.

Epoxy coating applications.
Epoxy tableware application.

Epoxied are from the chemical group called epoxides which has the formulation of epoxied-oxide. The curing of epoxides is very hard and specific curing agents must be added to epoxides. Important curing agents for epoxides are acid anhydrides and polyamines. And uncured epoxides have a very low degree of polymerization. So cross-linked molecular structures must be obtained for good mechanical strength and rigidity. Heat and chemical resistance are also very important properties of cured epoxides. Some of the applications of epoxides;

  • They are used in glass-fiber reinforced composites as adhesive agents.
  • Surface coating and industrial flooring applications of epoxies are also very important applications.
  • Epoxies are also very good electrical insulators. So they are generally used in electronic applications as insulative elements.

What are the Properties of Epichlorohydrin Thermoset?

Chemical representation of epichlorohydrin.

Epichlorohydrin has the chemical structure of C3H5OCl and this material’s curing agent is generally triethylamine which has the chemical representation of C6H5–CH2N–(CH3)2. Epichlorohydrin is a completely brittle material that has a 0% of elongation value according to its original shape. The production method of epichlorohydrin is the condensation polymerization method. The elasticity modulus of epichlorohydrin is around 7000 MPa and the tensile strength of epichlorohydrin is around 70 MPa.


These are the general important points on thermosetting polymers. You can find very different applications for them. According to their properties, they are very common in different kinds of engineering applications.

Finally, do not forget to leave your comments and questions below about the thermosetting polymers.

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What does thermoset mean?

The general meaning of the thermoset defines the cross-linking structure that occurs with the application of heat. So, they get solidified on a chemical basis. And if we try to melt it, we can not. Because cross-linked structures between the molecules prevent it.

What are examples of thermosets?

The most important example is epoxied. The applications of epoxies are very common in plastic coating applications. And phenolics are also a very important example of thermoset materials.

What are the 3 types of thermosets?

The 3 types are thermosets are; phenolics, epoxies, and thermoset silicones. You can find different kinds of engineering and manufacturing applications of them in the market.

What type of plastic is a thermoset?

Thermosets are a group of 3 classes of polymers that forms special cross-linked structures with the application of heat and UV light. With the formation of these cross-linking or curing, they create much stronger bonds between the molecules. And another important property is, they do not melt upon heating. Because the solidification of them takes place chemically.

Can thermosets be recycled?

The recycling of these materials is very hard. Because there is a chemical change in the molecular structure. And changing this molecular structure to the starting phase is very hard for thermoset materials. So, recycling these materials is not a common application.


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