Omar Bennett
Polymers are substances or materials composed of very large molecules called macromolecules, which are multiples of simpler chemical units called monomers. The number of monomers that constitute a polymer chain varies, and this is referred to as the degree of polymerization. The polymer's size may also be expressed in terms of molecular weight, with the number-average molecular weight (Mn) and weight-average molecular weight (Mw) being commonly reported. Synthetic polymerization techniques typically yield a range of chain lengths, and the molecular weight is expressed as a weighted average. The physical properties of polymers, such as viscosity, are strongly influenced by their length or molecular weight.
| Characteristics | Values |
|---|---|
| Definition of a polymer | A substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeating subunits derived from one or more species of monomers |
| Monomer definition | Smaller molecules that join together to make polymer chains by forming covalent bonds |
| Polymerization | The process of combining many small molecules known as monomers into a covalently bonded chain or network |
| Degree of polymerization | A common means of expressing the length of a chain by quantifying the number of monomers incorporated into the chain |
| Molecular weight | A polymer's size may also be expressed in terms of molecular weight |
| Number-average molecular weight | Mn, one of the most commonly reported molecular weights |
| Weight-average molecular weight | Mw, one of the most commonly reported molecular weights |
| Dispersity | The ratio of Mw/Mn, commonly used to express the width of the molecular weight distribution |
| Physical properties | The physical properties of a polymer depend on the length (or molecular weight) of the polymer chain |
| Examples of polymers | Natural polymers include silk, hair, proteins, DNA, cellulose, starches, and more; synthetic polymers include polyethylene, polypropylene, polyester, polystyrene, and more |
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What You'll Learn
Polymerization
The process of polymerization involves the creation of covalent bonds between monomers, which are formed when electrons are shared between them. This results in the formation of long chains of molecules, with the specific number of monomers incorporated into each chain influencing the length and properties of the resulting polymer. The length of a polymer chain can be expressed in terms of the degree of polymerization, quantifying the number of monomers present, or through molecular weight calculations.
There are two primary types of polymerization: step-growth polymerization and chain polymerization. In step-growth polymerization, chains of monomers combine directly with one another, and an additional small molecule, such as water, may be created as a byproduct. An example of this process is the formation of polyester. On the other hand, in chain polymerization, monomers are added to the growing chain one at a time. Polystyrene is an example of a polymer formed through this method.
The specific type of polymerization process and the arrangement of molecules within the polymer chains influence the resulting polymer's properties. For instance, varying the length and molecular structure of polymer chains can lead to the development of different polymers with distinct characteristics, such as strength, flexibility, heat resistance, and recyclability. Additionally, the presence of different side groups on the polymer chains can enable ionic bonding or hydrogen bonding between adjacent chains, further modifying the polymer's characteristics.
The broad spectrum of properties attainable through polymerization processes contributes to the ubiquitous presence of polymers in everyday life. Both natural and synthetic polymers play essential roles, with natural polymers such as DNA, proteins, and starches being fundamental to biological structures and functions, while synthetic polymers like polystyrene and polyethylene are commonly used in various products and materials.
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Synthetic vs natural polymers
Polymers are substances composed of very large molecules called macromolecules, which are multiples of simpler chemical units called monomers. The number of monomers in a polymer chain varies, and this flexibility is reflected in the term "polymer", which designates an unspecified number of monomer units. When the number of monomers is very large, the compound is sometimes called a high polymer.
Polymers can be natural or synthetic. Natural polymers are obtained from plants and animals, and include starch, cellulose, proteins, and natural rubber. Starch, for example, is a polymer composed of glucose, and it forms the food reserve for plants. Natural polymers are also biocompatible and biodegradable, making them useful in drug delivery systems.
Synthetic polymers, on the other hand, are man-made polymers synthesized in laboratories. They find a wide range of applications in our daily lives, with most of the things we use being made of synthetic polymers. Examples of synthetic polymers include polyethylene, polyvinyl chloride, Bakelite, nylon, and synthetic rubbers. Synthetic polymers are also used in biomedical implants and devices due to their ability to be fabricated into various shapes.
The process of combining monomers to form polymers is called polymerization. Synthetic polymerization techniques typically yield a statistical distribution of chain lengths, and the molecular weight is expressed in terms of weighted averages. The physical properties of a polymer strongly depend on the length of the polymer chain. For example, the viscosity of a polymer, or its resistance to flow, is influenced by the molecular weight.
Both natural and synthetic polymers play essential roles in our everyday lives due to their broad spectrum of properties. Polymers provide the basic structural materials for living things and participate in vital life processes. They are also the basis of many minerals and man-made materials, such as concrete, glass, paper, plastics, and rubbers.
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Polymer chains and networks
A polymer is a substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeating subunits derived from one or more types of simpler chemical units called monomers. The monomers are covalently bonded together to form long chains. The number of monomers that constitute a polymer chain varies, and when the number of monomers is very large, the compound is sometimes called a high polymer. The degree of polymerization quantifies the number of monomers incorporated into the chain.
The polymer chains can have different architectures depending on the structure of the monomer and the polymerization method employed. If the monomer segments are connected through carbon atoms, a linear polymer chain results. Sometimes, a polymer chain can have segments branching off of the main carbon backbone. Branched polymer molecules cannot pack together as closely as linear molecules, so the forces holding these polymers together are weaker. When the branches on a polymer chain further react or connect with neighbouring chains, the result is a network structure.
Polymer networks containing chemical bonds are called cross-linked polymers. The properties of network polymers depend on the density of the network. Polymers with a dense network are very rigid and sometimes even brittle. On the other hand, polymers with long, flexible branches connected at only a few sites along the chains are rubbery and exhibit elastic properties. The connections between polymer chains that form the network structures can vary in strength, with strong connections resulting from covalent or ionic chemical bonds, and weaker connections resulting from hydrogen bonds or Van Der Waals forces.
The attractive forces between polymer chains play a large part in determining the polymer's properties. The intermolecular forces in polymers can be affected by dipoles in the monomer units. Polymers containing amide or carbonyl groups can form hydrogen bonds between adjacent chains, resulting in higher tensile strength and crystalline melting points.
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Polymer properties
Polymers are natural or synthetic substances composed of very large molecules called macromolecules. They are formed by the polymerization of many small molecules called monomers. The number of monomers in a polymer chain can vary, and this length is quantified by the degree of polymerization. The properties of a polymer depend on its length, or molecular weight, with longer chains generally resulting in stronger polymers.
The structure of a polymeric material can be described at different length scales, from the sub-nm length scale up to the macroscopic. The microstructure of a polymer describes the arrangement of monomers within a single chain and plays a major role in determining the polymer's physical and chemical properties. The architecture and shape of a polymer, including the presence of branch points and side chains, also affect its physical properties such as solution viscosity, melt viscosity, solubility, and glass-transition temperature.
The attractive forces between polymer chains, including hydrogen bonding, influence the polymer's properties. These intermolecular forces are amplified due to the long chain lengths, resulting in higher tensile strength and crystalline melting points. The presence of specific side groups on the polymer chains can also affect these properties. For example, polar side groups can lead to stronger attraction between the chains, making the polymer stronger.
The physical properties of polymers can be modified by adding stabilizers or plasticizers. Stabilizers increase the resistance to oxidation, heat, or light and can act as flame retardants. Plasticizers increase flexibility by reducing friction between molecules, allowing for easier movement of the polymer chains.
Polymers have a broad spectrum of properties and play essential roles in everyday life. They can be natural biopolymers, such as DNA and proteins, or synthetic polymers like polystyrene and polyvinyl chloride (PVC). The unique properties of polymers, including toughness, high elasticity, and viscoelasticity, make them ubiquitous in both biological systems and man-made materials.
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Polymer nomenclature
Polymers are substances composed of very large molecules called macromolecules, which are multiples of simpler chemical units called monomers. Polymerization is the process of combining many small molecules, or monomers, into a covalently bonded chain or network. The number of monomers that constitute a polymer chain can vary, and this length is referred to as the degree of polymerization.
Source-Based Nomenclature
Source-based nomenclature is used when the monomer from which the polymer is synthesized can be identified. The polymer's name is intended to reflect the monomer(s) used in its synthesis, rather than the precise nature of the repeating subunit. For example, the polymer synthesized from the simple alkene ethene is called polyethene, retaining the -ene suffix even though the double bond is removed during polymerization.
Structure-Based Nomenclature
Structure-based nomenclature, on the other hand, is used when the polymer's structure is known. This approach is based on naming the preferred constitutional repeating unit (CRU) of the polymer. The smallest repeating portion of the polymer chain is identified as the CRU. All possible subunits that make up this structure are then identified using IUPAC nomenclature of organic chemistry.
Traditional Names
When there is no ambiguity, traditional names for some well-known polymers are also acceptable, such as polyethylene, polypropylene, and polystyrene. These names are retained when they fit into the general pattern of systematic nomenclature.
Non-Linear Polymers and Copolymers
Non-linear polymers, copolymers, and polymer assemblies are named using specific qualifiers, such as "branch," which can be used as a prefix or connective between two polymer names. Inorganic polymers, such as those containing metallocene derivatives, are named using organic nomenclature, with the seniority of elements differing from organic nomenclature.
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Frequently asked questions
There is no fixed number of monomers that constitute a polymer chain. The number varies depending on the polymer and the method of polymerization. Polymerization is the process of combining many small molecules called monomers into a chain or network. The length of a polymer chain is often expressed in terms of molecular weight.
When the number of monomers in a polymer is very large, the compound is sometimes referred to as a "high polymer". An example of a high polymer is polyvinyl chloride (PVC), which is synthesized from repeating units of vinyl chloride monomers.
Two common methods of polymerization are step-growth polymerization and chain polymerization. In step-growth polymerization, chains of monomers combine with one another directly, as seen in the formation of polyester. In chain polymerization, monomers are added to the chain one at a time, as in the synthesis of polystyrene.
Monomers join together to form polymer chains by creating covalent bonds, or sharing electrons. The polymer chains are held together by intermolecular forces, such as ionic bonding or hydrogen bonding, which influence the properties of the resulting polymer.
