Unsaturated Polyester Resin, Fiber Glass Resin

Unsaturated Polyester Resin

Unsaturated polyester resin, often abbreviated as UPR, is a versatile and widely used type of thermosetting polymer that plays a pivotal role in various industries, including construction, composites manufacturing, and artistry. This remarkable resin’s ability to combine with reinforcing materials, cure under controlled conditions, and form durable, lightweight, and corrosion-resistant structures has earned it a prominent place in the world of materials science and engineering. In this comprehensive article, we will delve into the world of unsaturated polyester resin, exploring its composition, applications, manufacturing process, and its significance in creating composite materials, artificial stone, sculptures, and more

1. Composition of Unsaturated Polyester Resin

1.1 Components of UPR

Unsaturated polyester resin is a complex chemical formulation primarily composed of three essential components:

a. Diol: Diol, short for “diethylene glycol,” serves as the foundational building block of UPR. This viscous, colorless liquid is a crucial component, contributing to the resin’s viscosity and handling characteristics.

b. Saturated and Unsaturated Anhydrides: These anhydrides, often phthalic anhydride or maleic anhydride, bring the reactive sites necessary for polymerization. Saturated anhydrides enhance the resin’s durability and adhesion properties, while unsaturated anhydrides provide crosslinking sites for polymerization.

c. Initiators and Catalysts: Various initiators and catalysts are added to trigger the polymerization reaction. These substances vary depending on the specific formulation and desired curing characteristics.

1.2 The Role of Anhydrides

The choice of anhydrides in the resin formulation significantly impacts the final properties of UPR. Saturated anhydrides, such as phthalic anhydride, contribute to the resin’s toughness and chemical resistance. On the other hand, unsaturated anhydrides, like maleic anhydride, introduce reactive double bonds (C=C) into the polymer backbone, enabling crosslinking during curing.

The balance between saturated and unsaturated anhydrides determines the resin’s overall characteristics, including its flexibility, adhesion, and resistance to environmental factors. This balance can be tailored to suit specific applications, making UPR a versatile material.

2. Manufacturing Process

2.1 Condensation Reaction

The production of unsaturated polyester resin involves a condensation reaction between the diol and the anhydrides. This reaction forms ester linkages (-COO-) and releases water as a byproduct. The ester linkages are the fundamental units of the polymer chain.

The stoichiometric ratio of diol to anhydrides is carefully controlled to achieve the desired resin properties. Excess anhydride can lead to brittle resins, while excess diol can result in a tacky and poorly cured material.

2.2 Catalysts and Initiators

The curing process of UPR relies on the use of catalysts and initiators. These chemicals accelerate the polymerization reaction and enable it to proceed at manageable temperatures. Common initiators include peroxides or organic peresters, while catalysts may include cobalt or amine compounds.

The choice of initiator and catalyst can be tailored to achieve specific curing times and temperatures, making UPR adaptable to various manufacturing processes.

2.3 Crosslinking Mechanism

During curing, the unsaturated double bonds in the resin’s molecular structure react with the initiators, forming highly reactive free radicals. These free radicals initiate a chain reaction, leading to the crosslinking of polymer chains.

This crosslinking process imparts strength and stability to the resin, transforming it from a liquid into a solid, three-dimensional network. The degree of crosslinking can be controlled to achieve the desired mechanical properties.

3. Properties of Unsaturated Polyester Resin

3.1 Mechanical Properties

Unsaturated polyester resin offers a wide range of mechanical properties depending on its formulation. It can be tailored to provide high tensile strength, flexibility, impact resistance, and dimensional stability. These characteristics make it ideal for use in construction and composite materials.

3.2 Chemical Resistance

UPR exhibits excellent resistance to many chemicals, including acids, bases, and various solvents. This chemical resistance makes it suitable for applications where exposure to corrosive environments is a concern.

3.3 Thermal Stability

The thermal stability of UPR can be enhanced by modifying its formulation. While it may not withstand extremely high temperatures, it is well-suited for many applications where moderate heat resistance is required.

3.4 Environmental Impact

It’s important to note that traditional UPR formulations may have environmental concerns due to the use of petrochemical-derived raw materials. However, advancements in sustainable chemistry have led to the development of eco-friendly UPR options that use bio-based or recycled materials. These innovations aim to reduce the resin’s environmental footprint.

4. Applications

Unsaturated polyester resin finds extensive use in various industries, owing to its versatility and advantageous properties.

4.1 Construction Industry

In the construction sector, UPR is commonly used as a binder for composite materials. It forms a matrix that holds together reinforcing materials like fiberglass, carbon fiber, or natural fibers. This results in the creation of composite materials with exceptional strength-to-weight ratios, making them suitable for structural components such as panels, beams, and facades.

Moreover, UPR-based composites are corrosion-resistant, making them ideal for outdoor applications where exposure to harsh environmental conditions is a concern.

4.2 Composite Manufacturing

The use of unsaturated polyester resin is prevalent in composite manufacturing across various industries, including aerospace, automotive, marine, and wind energy. Composites made with UPR offer reduced weight, increased strength, and improved durability, making them valuable for components like aircraft parts, car body panels, boat hulls, and wind turbine blades.

4.3 Artificial Stone Production

Unsaturated polyester resin is also employed in the production of artificial stone. When combined with fillers, pigments, and additives, UPR can create stone-like materials that mimic the appearance and texture of natural stone. These artificial stones are used in counter tops.

Orthophthalic and Isophthalic Unsaturated Polyester Resin: Differences and Applications

Unsaturated polyester resins (UPRs) are incredibly versatile materials with a wide range of applications in industries such as construction, composites manufacturing, and artistry. Within the realm of UPRs, two prominent categories are orthophthalic and isophthalic unsaturated polyester resins. In this article, we’ll explore the differences between these two types of UPRs and delve into their respective applications.

Orthophthalic Unsaturated Polyester Resin


Orthophthalic unsaturated polyester resin, often referred to as ortho resin, is a type of UPR derived from orthophthalic anhydride. It is typically combined with diethylene glycol (DEG) and maleic anhydride to create a versatile polymer matrix.


  1. Economical: Ortho resin is cost-effective and widely used in applications where premium performance isn’t necessary.

  2. Standard Performance: It exhibits moderate mechanical properties, making it suitable for various applications without specialized requirements.

  3. General-Purpose: Ortho resin is commonly utilized for general-purpose laminates and coatings.

  4. Corrosion Resistance: It offers decent resistance to corrosion but may not be the best choice for highly corrosive environments.


Orthophthalic unsaturated polyester resin finds application in:

  • Fiberglass Reinforced Plastics (FRP): It is used for producing FRP products such as pipes, tanks, and boat hulls.

  • Laminates: Ortho resin is employed in laminating materials for surfboards, bathroom fixtures, and lightweight panels.

  • Coatings: It is used in various coating applications, providing protection and aesthetics.

Isophthalic Unsaturated Polyester Resin


Isophthalic unsaturated polyester resin, commonly referred to as iso resin, is synthesized using isophthalic acid or its anhydride along with diethylene glycol (DEG) and maleic anhydride.


  1. Enhanced Performance: Isophthalic resin exhibits improved mechanical properties, including greater strength, toughness, and dimensional stability.

  2. Chemical Resistance: It offers excellent resistance to chemicals and corrosion, making it suitable for harsh environments.

  3. Low Shrinkage: Iso resin has lower shrinkage during curing, resulting in better mold replication and less distortion.

  4. High Heat Resistance: It possesses superior heat resistance, making it suitable for applications exposed to elevated temperatures.


Isophthalic unsaturated polyester resin is employed in a variety of specialized applications, including:

  • Chemical Storage Tanks: Its exceptional chemical resistance makes it ideal for manufacturing tanks and vessels used to store corrosive chemicals.

  • Marine and Automotive Parts: Iso resin is used to create components for marine vessels and automobiles, where durability and resistance to saltwater are crucial.

  • Aerospace: It finds use in aerospace components where lightweight materials with high strength are essential.

  • Corrosion-Resistant Structures: Iso resin is used in the construction of structures like fume hoods and chemical processing equipment.

Differences Between Orthophthalic and Isophthalic Unsaturated Polyester Resins

1. Chemical Composition

The primary difference between ortho and iso resins lies in their chemical composition. Orthophthalic resin is derived from orthophthalic anhydride, while isophthalic resin uses isophthalic acid or anhydride. This distinction affects their performance characteristics.

2. Performance

Isophthalic unsaturated polyester resin generally outperforms orthophthalic resin in terms of mechanical properties, chemical resistance, and heat resistance. Isophthalic resin is the preferred choice for applications where enhanced performance is required, especially in corrosive environments.

3. Cost

Orthophthalic resin is typically more cost-effective than isophthalic resin, which is why it is often used in applications where premium performance is not necessary.

4. Applications

While orthophthalic resin is suitable for general-purpose applications, isophthalic resin is chosen for more demanding situations where resistance to chemicals, corrosion, and heat is essential.

Syntive stands as a preeminent unsaturated polyester resin manufacturer, renowned for its unwavering commitment to delivering products of the utmost quality at competitive prices. With a rich history of innovation and excellence, we have earned the trust of industries worldwide. Our unsaturated polyester resins, including orthophthalic and isophthalic variants, are crafted to meet and exceed industry standards, ensuring exceptional mechanical properties, chemical resistance, and dimensional stability.

What sets Syntive apart is our relentless pursuit of balance between superior quality and affordability. We believe that excellence shouldn’t come at a premium, and our dedication to cost-effective solutions has made us the preferred choice for clients seeking top-notch materials without compromising their bottom line. Our team of experts is committed to working closely with customers, tailoring resin formulations to meet their specific needs, and providing expert guidance to ensure they get the best value for their projects. At Syntive, we don’t just offer unsaturated polyester resins; we offer a partnership built on trust, quality, and affordability

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