Copolymer: Definition, Properties, Types, and Examples
Copolymer is a classification of thermoplastic materials. It is composed of polymerized chains of two or more chemically differentiated monomers that are covalently bonded together in a long, strong polymer chain. Copolymers can have a variety of arrangements of monomers in the chain, resulting in a wide spectrum of mechanical, thermal, and chemical properties and material classifications. These chain arrangements include: random, alternating, block, graft, or what are referred to as statistical distributions of monomers.
This article will discuss copolymers, their properties and types, and provide some examples.
A copolymer belongs to the family of polymers formed by the cooperative polymerization of two or more different monomers in a closely coupled combination chain. This blending of divergent monomers leads to the creation of copolymers with diverse properties. These can be tailored, and even finely adjusted for specific application demands.
Copolymers are structurally differentiated into categories, derived from the arrangement of the two or more monomers within the polymer chain. These categories include: random, alternating, block, graft, and statistical.
Copolymers are used across all industries because of their ability to be fine-tuned for precise property needs. They can be selectively and predictably engineered for improved flexibility, durability, chemical resistance, and a range of other specific characteristics, by choosing the appropriate combination of monomers and polymerization techniques.
No. While all copolymers are polymers, not all polymers are copolymers. So no, a copolymer is not the same as a polymer. While both copolymers and polymers are large molecules composed of repeating structural units called monomers, they differ in their composition. Polymer is a broad term encompassing any large molecule formed by the repetitive bonding of monomers. A copolymer, on the other hand, is a subtype of polymer formed by the polymerization of two or more different monomers.
To learn more, see our guide on Polymer Material.
Copolymers have diverse applications across all industries. This results from their diversity, versatility, and the ability to tune properties by combining multiple monomers in a single material. Some of their uses are listed below:
- Production of engineering plastics, whereby they can be precisely designed to exhibit specific characteristics like: flexibility, toughness, or transparency.
- Can form the basis of adhesives and sealants, offering strong bonding capabilities and flexibility. Ethylene-vinyl acetate (EVA) copolymers, for instance, are used in hot melt adhesives.
- Biocompatible copolymers like poly(lactic-co-glycolic acid) (PLGA) are used in medical implants, drug delivery systems, and tissue engineering due to their easy compatibility with living tissues.
- Ethylene vinyl alcohol (EVOH) is used as barrier layers in food packaging to prevent oxygen and moisture ingress, extending the shelf life of products.
- Can be employed to create fabrics with specific properties, such as moisture-wicking or flame resistance and self-extinguishing.
- Used in various automotive components, including: gaskets, hoses, and interior trim, to provide durability and flexibility.
Copolymers are synthesized through polymerization. Polymerization involves the repetitive coupling of monomers to form long-chain macro-molecules. The various methods of copolymer synthesis depend on the desired composition, properties, and structure of the copolymer. Copolymers are created by using two or more different monomers that will define many of the properties of the resulting material. There are several methods of polymerization, including addition and condensation polymerization. In addition to polymerization, monomers with reactive groups (often double carbon bonds) are linked together in a chain. This encompasses both free radical and anionic polymerization. In condensation polymerization, monomers with functional groups (often ester or amide groups) react to form a polymer, generally with the elimination of a water or methanol molecule.
During the polymerization process, the selected monomers are combined in the desired ratio to create the copolymer. The sequence of monomers and their arrangement along the polymer chain can be controlled for specific properties. Initiators (addition polymerization) or catalysts (condensation polymerization) are then generally employed to start and facilitate the polymerization process. The resulting copolymer will usually need to undergo purification steps to remove any unreacted monomers, impurities, or catalyst residues. Finally, the copolymer is characterized to confirm its composition, molecular weight, and properties, often using techniques like: spectroscopy, chromatography, and X-ray diffraction.
The details of the copolymerization process can vary significantly based on the selected monomers, the desired copolymer structure, and the polymerization conditions, such as: pressure, temperature, and catalyst or initiator choice.
The diversity of properties of materials that can be considered as copolymers is extensive. Table 1 below lists some of the most common properties:
Can be designed with a high degree of precision in selecting and adjusting properties by choice of monomers, their proportions, and the mechanics of chain construction.
Regularly engineered for high tensile strength.
Flexibility/ elasticity/ rigidity
Can be tuned to be flexible or rigid depending on the choice of monomers and the molecular complexity/simplicity of construction.
Is often designed for specific resistance to groups of chemicals.
Have widely varying and adjustable degrees of thermal stability.
Certain copolymers have been derived to conduct electricity.
Some copolymers are transparent and optically clear.
Can be designed to have excellent barrier properties against gases, moisture, or chemicals.
Is engineered to be biocompatible for use in medical implants and treatment systems.
Some copolymers are developed for strong adhesion to various classes of other materials.
Can be designed for flame retardancy.
UV and Ionizing Radiation Resistance
Can be formulated to resist various degrees of radiation damage.
Has varied molecular weights, resulting from chain complexity, whereby simpler chains can lie in closer association, firming crystalline regions.
Many copolymers are easily processed using standard thermoplastic techniques like: injection molding, extrusion, or blow molding.
The different types of linear copolymers are listed and discussed below:
Block copolymers are characterized by the arrangement of two or more distinct polymer blocks in a linear or branched chain. Each block consists of a series of repeating monomer units that are chemically different from the neighboring block(s). Block copolymers exhibit a range of unique properties, in particular microphase separation, in which the divergent blocks self-assemble into well-defined domains. This results in materials with a combination of characteristics from each block, offering tunable properties like: flexibility, toughness, and rigidity.
Gradient or gradient-index copolymers are a specialized type in which the composition of monomers gradually changes along the polymer chain. This gradual transition results in chains with unique properties that vary smoothly from one end to the other.
Gradient copolymers offer improved adhesion at interfaces, and the ability to fine-tune material-chemical interaction characteristics. They find applications in biomaterials, coatings, adhesives, and responsive materials in which the gradual change in properties allows for better performance in diverse conditions.
Statistical copolymers, also known as random copolymers, are a type in which two or more monomers are randomly distributed along the polymer chain. The distribution of monomers can be statistically random or follow a specific statistical pattern.
The properties they deliver, including flexibility, thermal stability, chemical resistance, etc, can be manipulated by adjusting the monomers and their proportions. Statistical copolymers are common materials with a combination of adjustable characteristics that can be tuned extensively, to meet specific demands.
Periodic or alternating copolymers are those in which two or more monomers are arranged in a regular, repeating pattern along the polymer chain. Unlike statistical copolymers with randomly distributed monomers, periodic copolymers exhibit a precise and predictable sequence of monomer units.
This precise arrangement leads to unique and well-defined material properties. Their controlled structures are valuable in applications in which specific and consistent properties are required, such as in: semiconductors, optical materials, and specialty coatings.
Alternating copolymers are a specific type in which two distinct monomers alternate regularly in a monomer pattern ABABAB or ABn. This controlled arrangement leads to unique material properties, making them valuable in various applications, such as: semiconductors, specialty plastics, and organic electronics. They often exhibit specific behaviors, such as enhanced charge transport in electronic devices or improved selectivity in separation membranes.
Stereoblock copolymers are copolymers consisting of two or more blocks, each composed of isotactic (aligned stereochemistry) or syndiotactic (alternating stereochemistry) sequences. These sequences are linked together to form a single polymer chain. Stereoblock copolymers combine the properties of isotactic and syndiotactic polymers within a single molecule. This unique structure leads to distinct material properties, such as: improved crystallinity, higher melting points, and enhanced mechanical strength.
The different types of branched copolymers are listed and discussed below:
Stars or star-shaped are a unique class of copolymers characterized by a central core with multiple polymer arms radiating outward resembling a star. These arms consist of polymer chains composed of a different monomer. Star copolymers offer several advantages due to their distinctive architecture, such as: tunable properties, enhanced solubility, self-assembly in nano-structures, multifunctionality on a per-arm basis, and low polydispersity (narrow band of molecular weight).
Applications of star copolymers span various industries, including: pharmaceuticals, coatings, and advanced materials. They are used in drug delivery systems, in nanocomposites for enhancing material properties, and in lithography for creating nanoscale patterns.
Graft copolymers are a distinctive class composed of two or more types of polymer chains. They consist of one type of polymer (the main chain or backbone) to which side chains (the grafts) composed of another type of polymer are attached. These side chains can have a different chemical structure and properties than the main chain.
This offers various beneficial properties such as: versatility and tunability of properties, enhanced compatibility/bonding with other materials according to graft chemistry, improved properties from graft selection, acting as toughening additives for other polymers, and aiding nanomaterial dispersion into other chemistries.
The advantages of copolymerization are listed below:
- Allows for the precise control and tailoring of material properties by selecting and adjusting the monomer composition and sequence.
- Often exhibit properties that are not achievable with homopolymers, such as improved mechanical strength and chemical resistance.
- Can lead to more cost-effective materials, by substituting for metals or more complex materials.
- Can be used to enhance compatibility/miscibility between otherwise incompatible materials.
- Regularly results in the discovery of novel materials with unique properties.
While copolymerization offers numerous advantages, it also comes with certain burdens and challenges such as:
- Often more complex than homopolymerization due to the need to manage the reactivity of multiple materials.
- Monomers may have different reactivity rates, leading to difficulties in achieving a well-controlled copolymer composition and sequence.
- Achieving specific material properties in copolymers may be less predictable than in homopolymers, in some cases.
- Generally involves the use of multiple monomers and additional process complexity, which increases production costs.
- Monomers are not universally compatible, preventing the establishment of some copolymers and making others very much harder to process.
Copolymers, like many other materials, can be safe for the skin when appropriately specified/designed and purified. However, the safety of copolymers depends on various factors, including: the specific copolymer composition, its intended use, and potential exposure levels.
In general, copolymers that have been fully tested and evaluated for safety, and are used in formulations that comply with regulatory standards, are considered safe for skin contact.
Some key and widely employed copolymers are listed below:
- Styrene-butadiene rubber (SBR)
- Ethylene-vinyl acetate (EVA)
- Polycarbonate (PC)
- Nylon 6/6
- Acrylonitrile butadiene styrene (ABS)
No. Polyvinyl chloride, commonly known as PVC, is a polymer; not a copolymer but a homopolymer. It consists of a single type of monomer (vinyl chloride) covalently bonded into long chains.
No. Teflon® is the DuPont branding for the original form of polytetrafluoroethylene (PTFE). This is not a copolymer, being formed by the polymerization of tetrafluoroethylene (TFE) monomer. Many copolymers that utilize this monomer with enhancement by other monomers can be identified across the plastics industry.
No. Silicone polymers (polysiloxanes) are not copolymers. While silicone polymers do contain silicon (Si) and oxygen (O) atoms in their chain, they are formed from the polymerization of one monomer, siloxane.
To learn more, see our guide on What Material is Silicone.
A copolymer is composed of two or more different monomers that are chemically bonded together and repeated in a regular or random pattern along the polymer chain. They possess a uniform and homogenous structure along the polymer chain, however complex the side branching present in the structure. Homopolymers, on the other hand, are chemically simpler, being formed from only one monomer that can be both spine and side branch on the same polymer chain.
To learn more, see our Colypolymer and Homopolymer guide.
This article presented copolymers, explained them, and discussed their properties and various types. To learn more about copolymers, contact a Xometry representative.
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- Teflon® is a registered trademark and a brand name owned by Chemours (formally DuPont)
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